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Two free base meso-tetraphenylporphyrin-fullerene dyads, H2PMe-C60, H2POMe-C60, and their zinc complexes, ZnPMe-C60 and ZnPOMe-C60, which the para positions of the meso-tetrasubstituted phenyl groups of the porphyrin core were substituted by methyl(-Me) and methoxyl(-OMe) groups respectively, were synthesized. The porphyrin unit in the synthesized dyads is directly linked to the fullerene entity through the pyrrole-β- position rather than through the traditionally meso-substituted phenyl group, which may be more favorable for electron communication between the donor and the acceptor. They are fully characterized by mass spectrometry, nuclear magnetic resonance, infrared spectroscopy and ultraviolet visible spectroscopy. Experimental results obtained from steady-state fluorescence spectroscopy and cyclic voltammetry show that the coordination of the zinc ions lead to an increase in the singlet excited state energy of the metallated porphyrin unit by about 0.15 eV, and to a reduce in the HOMO level and in the HOMO-LUMO energy gap. The molecular reorganization energy decreases after the electron-donating groups of -Me or -OMe attaching to the para position of the meso-phenyl group of the porphyrin moiety. The results of the energy calculations show that photoinduced electron transfer is thermodynamically favorable for the synthesized porphyrin-C60 dyads. There exists a competition between the photoinduced electron transfer and energy transfer processes from the first singlet excited state of porphyrin core to fullerene moiety. The photoinduced electron transfer rate constant of the dyads were calculated according to Marcus theory. The results indicate that the coordination of metal zinc ions lead to great increase in the electron transfer rate constant. Further, the photoinduced electron transfer rate constant increases in the order ZnP-C60, ZnPMe-C60, ZnPOMe-C60.

In this effort, the correlation between polymer immobilization effect and excited state of emitting copper complex was discussed. An electron-pulling diamine ligand having an oxadiazole ring and a fluorine atom was synthesized. Its corresponding Cu(I) complex was synthesized with a phosphorous ligand (PPh3) having obvious steric hindrance as auxiliary ligand. Its geometric structure, electronic transition and photophysical parameters were discussed in detail. A distorted tetrahedral coordination field was adopted by this Cu(I) complex. Its onset electronic transition was confirmed as a charge transfer one and suffered from structural relaxation badly. Using electrospinning method, this Cu(I) complex was dispersed and immobilized into a polymer host so that structural relaxation of its excited state could be limited. A systematical comparison between various states of this complex, in solution, in solid state and in fibrous samples, was performed. It was finally confirmed that this polymer matrix served as a promising supporting host, offering a rigid and protective microenvironment for dopant molecules which effectively limited their MLCT structural relaxation and improved their photostability.

Synthetic dyes having high photostability on hydrophobic fibers such as poly(ethylene terephthalate) (PET) are of interest for use on textile substrates for outdoor applications. While much is known about photostable dyes developed for PET in the 1980s, owing to their viability for use in automobile interiors, little has been published on currently viable photostable disperse dyes. As part of an effort to help fill this void and to facilitate future photostable disperse dye design, the present study involved the use of experimental measurements and modelling studies to help characterize the molecular structures of commercially viable dyes for producing photostable colors on PET fibers, beginning with a pair of blue dyes. With the aid of HR-MS, 500 MHz 1H NMR, and X-ray crystallography, it was established that the two dyes are structural isomers having 1,5-(OH)2-anthraquinone (AQ) and 1,8-(OH)2-AQ base structures. It is proposed that the photostability of these dyes arises from the presence of multiple OH/NH groups ortho to the AQ C O groups which enables them to dissipate excited state energy through intramolecular proton transfer. Further, using DFT-based molecular modelling studies, it was shown that the dye having the 1,5-(OH)2-AQ base structure has a lower ESOP than the isomeric dye having the 1,8-(OH)2-AQ base structure. Similarly, results from calculating Frontier HOMO and LUMO isosurfaces indicated that the LUMO lobes of the latter dye are larger, suggesting that this dye undergoes excitation faster than the 1,5-(OH)2-AQ isomer.

Steady state and time resolved spectral properties of 7,8-benzoquinoline (7,8-BQ) have been reinvestigated in a series of organic solvents of different proticity, polarity and wide range of pH. The salient features of this work are the effect of hydrogen bonding in protonation reaction which is explored through its behaviour in water and strong hydrogen bond donating solvent (trifluoroethanol). Quantum yield and rates (radiative, non-radiative and excited state protonation) have been calculated and discussed. Irreversible diffusion controlled excited state proton transfer in water and faster excited state protonation in trifluoroethanol is observed.

Since acenaphthene isolated in an Ar matrix at 15 K emits green-yellow phosphorescence for ∼10 s after stopping UV-light irradiation, its transient IR spectrum is expected to be measured with an FTIR spectrometer during UV irradiation. The transient spectrum observed is found to be consistent with the simulated spectrum of acenaphthene in the lowest electronically excited triplet (T1) state calculated at the B3LYP/6–31++G(d,p) level. The spectral pattern obtained using the B3LYP functional, which is the most popular DFT hybrid functional, reproduces the observed spectrum more satisfactorily than that obtained using the recently proposed M06-2x functional, although the optimized geometrical parameters in the both calculations are not so different from each other. The IR-band assignments of the T1 state and the structural changes from the S0 state to the T1 state are discussed based on the results of B3LYP calculation.

The radiationless decay of the isothiazole and thiazole molecules in the gas phase is investigated by a combination of static MS-CASPT2 computations with dynamics simulations, and some deactivation pathways are identified leading from the lowest excited singlet (S1) state back to the electronic ground (S0) state. The dominant relaxation pathway of the excited isothiazole is found to involve out-of-plane ring deformation (ring puckering) at the C4=C5(H8) S1 moiety, while the excited-state decay of thiazole can proceed through the ring puckering and S1 C2 bond cleavage pathways both of which happen at the S1 C2(H6) = N3 moiety. On the basis of the calculation results, we suggest that both ring-puckering and ring-opening routes should play rather important roles in the photophysics and photochemistry of heterocyclic molecules, and the position of the N atom in the heterocyclic ring has an effect on the excited state deactivation.

Two novel molecules (SCLPY-MeO and SCLPY-CN) are designed based on the N-salycilidene-5-chloroaminopyridine (SCLPY) via introducing the methoxyl (-OCH3) and cyano (-CN) groups at the meta-position of the chlorine atom, respectively, to explore the effect of the substitution of electron-withdrawing and donating groups on the excited-state intramolecular proton transfer (ESIPT) mechanism and photophysical properties of SCLPY, employing the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The significant calculated structural parameters associated with the intramolecular hydrogen bonds (IHBs) have demonstrated that the IHBs intensity is enhanced in the excited state and SCLPY is endowed with the strongest IHB. The partial quenching of the short-wavelength fluorescence in SCLPY-CN has been satisfactorily explained by calculating the transition electric dipole moment and the long-wavelength fluorescence of that exhibits the largest Stokes shifts relative to the other molecules. Moreover, introducing the -OCH3 group has evidently enhanced the luminescent intensity of SCLPY. On account of the potential energy curves (PECs), scanning with gradually elongating the O1-H2 bond, it can be known that the forward proton transfer process is more readily to occur in the S1 state due to the relatively lower energy barriers compared with the ground state. Moreover, SCLPY is provided with the lowest energy barrier, implying that the ESIPT behavior is most likely inclined to proceed in SCLPY. Therefore, it is well illustrated that the introductions of -OCH3 and –CN groups indeed have an impact on the ESIPT process and photophysical properties of SCLPY.

In this work, two luminescent iridium complexes were synthesized with 2-phenyl pyridine (ppy) and two phosphine-based ligands. There was large steric hindrance in these phosphine-based ligands, so that there would be enough time for the excited state based on highly luminescent 3MLLCT (metal-to-ligand-ligand-charge-transfer) electronic transformation It was found that there was limited aggregation-induced phosphorescence emission (AIPE) effect in these two iridium complexes since their ligands with large steric hindrance minimized the intermolecular (π-π) interactions between molecules. A distorted octahedral coordination field was found in the single crystals of these two iridium complexes. A systematical comparison on the photophysical parameters of these two iridium complexes in solution state, in solid state and in electrospun fiber was carried out, so that the limited aggregation-caused quenching (ACQ) could be confirmed. The potential surface crossing and energy transfer in the excited state of these two iridium complexes were analyzed by means of density functional theory calculation and temperature-dependent emission spectra. The limited ACQ effect in these two iridium complexes was finally confirmed due to the large ligand steric hindrance, which allowed phosphorescent decay of excited state. High emission quantum yield (0.27) and long emissive lifetime (0.43 μs) in solid state were observed.

The molecular, spectroscopic, and excited state properties of synthetic dyes for fiber-based outdoor materials continue to be of commercial interest. Early developments in this area were reported in the 1980s, when the need for dyes for polyester (PET)-based automobile interiors gave rise to commercially viable nitrodiphenylamine yellow, anthraquinone red and blue, and azo red dyes. To augment that initial knowledge base, the present study involved the use of experimental and theoretical methods to help establish the molecular structures and excited state properties of some more recent dyes for producing photostable colors on PET fibers. Having completed the characterization of present-day scarlet, blue, and yellow disperse dyes for PET-based fibers used outdoors, our attention turned to commercially available red and violet dyes. In this regard, HPLC analysis showed that the red product was a mixture containing four components, while the violet product contained only one component. Results from 1H NMR, HRMS, and single crystal X-ray diffraction analyses indicated that the principal components were dyes having a 1-amino-4-hydroxyanthraquinone base structure. The presence of an –OH group alpha to an anthraquinone C=O moiety provides for intramolecular H-bonding and a subsequent opportunity for intramolecular proton transfer in the excited state – as a photostabilizing mechanism. Further, for both dyes, results from the analysis of Frontier HOMO and LUMO isosurfaces indicated strong HOMO-LUMO overlap without molecular gaps and were consistent with strong excited state energy dissipation in a non-destructive way.

This work was part of an investigation aimed at characterizing the molecular and excited state properties of currently available disperse dyes developed to provide stability to extensive sunlight exposures when adsorbed on poly(ethylene terephthalate) (PET) fibers. Having completed the characterization of yellow, magenta, and cyan disperse dyes for PET-based fabrics used outdoors, our attention turned to the colors designed to enhance the color gamut of a standard 4-member (cyan/yellow/magenta/black) color set. The present study pertained specifically to the characterization of commercially available scarlet dyes. In this regard, HPLC analysis showed that a scarlet product used for PET coloration was mainly a 70/30 mixture of dyes, and the use of HRMS and single crystal X-ray diffraction analyses indicated that these two dyes were azo compounds derived from isomeric pyridine-based couplers which differed in the location of the primary amino ( NH2) and anilino ( NHPh) groups attached to the pyridine ring. One dye structure has the NHPh group para to the azo group (Sc2), while the other has that group in the ortho position (Sc3). The presence of either ortho substituent provides photostabilization through intramolecular H-bonding with the azo moiety. Further, results from molecular modeling studies showed that the lower excited state oxidation potential of Sc3 relative to that of Sc2 allows Sc3 to function as an energy quencher for the excited state of Sc2 – through thermodynamically favorable electron transfer.

New hetero-stilbene derivatives, namely cis/trans-2/3/4-(2-vinylstyryl)pyridines, have been synthesized by Wittig reaction from the diphosphonium salt of α, α′-o-xylenedibromide, formaldehyde and 2/3/4-pyridinecarbaldehydes. The 2/3/4-(2-vinylstyryl)pyridines afforded, by photochemical intramolecular cycloaddition and cyclization reactions, diverse new polycyclic products with the pyridine ring integrated into the polycyclic skeletons. All of the new benzobicyclo[3.2.1]octadiene, benzobicyclo[2.1.1]hexene and vinyl- benzoquinoline products were identified and characterized by spectroscopic methods. Isomerized dihydro- intermediates *Revised Manuscript Click here to view linked References 2 (DHQs), that formed as a result of [1, n-H] shifts were also isolated, identified and characterized. DHQ intermediate isomers were never isolated in these conditions before.

Terpyridines containing substituted o-iminophenolic groups were synthesized. The obtained compounds possess two emission bands: with normal (at 480–495 nm) and anomalous Stokes shifts (at 509–569 nm) generated by the fast intramolecular O→N proton transfer in the singlet excited state (ESIPT effect). They represent bifunctional chromogenic “naked-eye” chemosensors for Cu2+ and Ni2+ due to their complexation with o-hydroxyimine fragment (change of the solution color from colorless to bright yellow) and for Fe2+ - due to complexation with the terpyridine moiety (colorless to violet).

Two free base porphyrins, 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin ( cis -DATPP), 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin ( trans -DATPP), and their zinc metalated analogues ( cis -ZnDATPP and trans -ZnDATPP) were synthesized. A series of their corresponding polyimides were obtained by the condensed polymerization of the respective monomeric isomer DATPP with a 1:1 ratio of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA). The inclusion of PFMB and 6FDA into the polymeric backbone causes the polymers to be moderately to highly soluble in organic polar solvents. The molar content of the respective DATPP monomer varied between 5 and 30%. All compounds were structurally characterized by 1 H NMR and ATR-IR spectroscopy and the porphyrin content in the polyimides was determined by UV–Visible absorption spectroscopy. Photophysical properties consisted of measuring both the UV–Visible (ground state) absorption and fluorescence (excited state) spectra, fluorescence quantum yields (Φ f ), and fluorescence lifetimes (τ f ) in dichloromethane and N,N-dimethylacetamide. Fluorescence quenching was also measured and observed by the Stern-Volmer relationship, using 9,10-anthraquinone (AQ) as the quencher molecule. Both the bimolecular rate constant of fluorescence quenching (k q ) and the Stern-Volmer constant (K Q ) were calculated from this relationship. Furthermore, deviations from linearity depicted in the Stern-Volmer plots for TPP and ZnTPP at higher concentrations of AQ were also measured as a means of examining and explaining the simultaneous occurrence of dynamic (collisional) quenching and static quenching in the mechanisms of fluorescence quenching. It was found in this work that the significantly larger values in the static quenching constant (K S ) than in the dynamic quenching constant (K D ) are indicative that static quenching and ground state complex formation between the fluorophore and quencher is the dominant mechanism of fluorescence quenching of these systems at higher quencher concentrations.

6-Aminouracils have extensively been used as precursors for synthesizing numerous uracil derivatives of biological and pharmaceutical significance. This study describes an application of 1,3-dimethyl-5-(arylazo)-6-aminouracils (Uazo: Uazo1-Uazo4, precursors) for an efficient synthesis of a series of 8-substituted-azapurins (AP), namely 1,3-dimethyl-8-(aryl)-azapurin-2,6-diones (aryl = p-HC6H4 (AP1), -MeC6H4 (AP2), ClC6H4 (AP3), and SO2NH2C6H4 (AP4)) following an oxidation method in the presence of copper (II) nitrate and in alkaline medium. The obtained compounds were isolated in good yields as crystalline air-stable products and have been fully characterized in the solution by UV–vis and NMR spectroscopy, as well as in the solid state by FT-IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (for AP2 and AP4). UV–vis study evidences that the conversion of the 6-aminouracil precursors occurs via an intermediate, Cu(II)-complex and a plausible mechanism for the formation of AP1-AP4 has been proposed. Unlike AP2 the crystal structure of AP4 reveals the formation of interdigitated 1D H-bonded chains that has been topologically classified within the 2C1 type. The 1H NMR spectra of the products have proton signals that completely devoid of hydrazone ( NH ) and imine (=NH) signals of their parent Uazo derivatives, thus confirming their full conversion and a stability of the AP1-AP4 in solution. The excitation and emission spectra of AP1-AP4 were also recorded in solution, revealing electronic transitions between similar vibrational energy levels of S0 (singlet ground state) and S1 (singlet first excited state).

Intra-molecularly hydrogen bonded compound 2-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid (ANQ) shows emission at single wavelength upon excitation in UV-region whereas it shows dual fluorescence emissions on excitation in visible region. Such emissions depend on solvent, concentration and pH. Solvent dependent structural changes of ANQ are reflected in solution studies carried out by 1 HNMR, UV–visible and fluorescence spectroscopy. DLS study has showed that in addition to monomers, self-assemblies with 415 nm average sized particles are formed in DMF solution. HOMO-LUMO of three tautomeric forms of the compound was calculated by DFT using CAMB3LYP/6-31 + G(d,p) as basis set shows that naphthoquinone form has about 86.30 kJ/mol higher stability over an imino-quinone form. From various studies relating concentration dependence, pH, life-time, study on dual-emissions caused by visible excitation has established the observed emissions to originate from aggregation contributing as charge-transfer and deprotonated species. Whereas the single emission caused by UV-excitation occurs through excited state intra-molecular proton transfer.

In the present work, the quantum theoretical calculations of the molecular structures of the four new synthesized azomethine dyes such as: 1. ( E )- N -(4-butoxybenzylidene)-4-(( E )-phenyldiazenyl)aniline (PAZB-6), 2. ( E )- N -(4-(benzyloxy)benzylidene)-4-(( E ))-phenyldiazenyl)aniline (PAZB-7), 3. 4-(( E )-4-(( E )-phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-8), 4. ( E )- N -(4-methoxybenzylidene)-4-(( E ))-phenyldiazenyl)aniline (PAZB-9) have been predicted using Density Functional Theory in the solvent Dimethylformamide. The geometries of the azomethine dyes were optimized by PBE1PBE/6-31+G* level of theory. The electronic spectra of the title compounds in the solvent DMF was carried out by TDPBE1PBE/6-31+G* method. FT-IR spectra of the title compounds are recorded and discussed. Frontier molecular orbitals, molecular electrostatic potential, electronic properties, natural charges and Natural Bond Orbital (NBO) analysis of the mentioned compounds were investigated and discussed by theoretical calculations. The azomethine dyes were synthesized after quantum chemical modeling for optical applications. A new study of anisotropy of thermal and electrical conductivity of the colored stretched PVA-films have been undertaken.

The UV–vis absorption and steady state fluorescence spectra of phenyl salicylate (abbreviated as PS) have been recorded in a series of non-polar, polar protic and polar aprotic solvents at room temperature and the obtained spectral data are used to determine the solvatochromic behavior and the ground and excited state dipole moments. Basis set sensitive molecular structure along with X-ray crystal data are evaluated. The ground state and excited state dipole moments are determined by using Lippert-Mataga, Bakhshiev, Bilot-Kawski and Reichardt solvatochromic shift methods as a function of dielectric constant ( e ) and refractive index ( n ) of the solvents. The larger excited state dipole moment value indicates the more polar PS in the excited state. The rate of μ e / μ g is found as 2.4239. Solvatochromic behavior of PS is enlightened by using Kamlet-Taft and Catalan models. Kamlet-Taft solvatochromic model indicates that non-specific solute solvent interactions are controlled by solvent dispersion-induction forces and specific interactions are directed by hydrogen-bond donor capacity of solvent. Catalan solvatochromic model designates that solute-solvent interactions are governed by solvent polarizability. Ground and excited state dipole moments are found theoretically by using DFT/B3LYP/6–311++G(d, p) and TDDFT/B3LYP/6–31++G(d, p) methods. External electric field effect on LUMO-HOMO band gap and dipole moment have been investigated by using B3LYP/6–311++G(d, p) method.

The optical properties of 4-methyl-9-(3-oxobutanoyl)-2H,8H-pyrano[2,3-f]chromene-2,8-dione was investigated in solvents of different polarity by employing UV–vis absorption and fluorescence spectroscopy at room temperature (298 K). A bathochromic shift is observed in absorption and fluorescence spectra of this molecule with increasing solvent polarity. Solvatochromic correlations were used to obtain the dipole moment in the ground and the first excited-state. The excited-state dipole moment was found to be larger than the ground-state dipole one.

The reaction of 1-isocyanatonaphthalene with hydrazine hydrate in presence of acetone resulted in the formation of napthyl based semicarbazone (1). The compound has been characterized using UV–Visible, FT-IR, NMR, mass spectroscopic and single crystal X-ray diffraction (XRD) tools. The interaction between 1 and fluoride ion has been investigated by means of UV–Visible and fluorescence spectra. The fluoride ion sensing mechanism of 1 has been studied by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) methods. The added fluoride ion formed intermolecular hydrogen bonds with the protons of N1 H1 and N2 H2 groups of 1 in the ground state. The N1 H1 proton which is closer to naphthalene moiety prefers to bind fluoride anion in the excited state after deprotonation, which lead to excited state proton transfer (ESPT). The fluoride ion sensing process shows a moderate (31.99 kcal/mol) Gibbs free energy. To understand the dynamic features, the transition state (TS) calculation is performed and the change in entropy is found to be −0.6259 kJ/mol, which shows that the sensing process is thermodynamically allowed.

The GdAl 3 (BO 3 ) 4 :Sm 3+ phosphors prepared by solid-state reaction method were characterized through thermal, structural and photoluminescence studies at room temperature only. The observed X-ray diffraction peaks were well consistent with JCPDS No. 83-1907. When excited with 406 nm wavelength, the studied phosphors exhibit orange-red luminescence through 4 G 5/2 → 6 H 5/2 , 4 G 5/2 → 6 H 7/2 and 4 G 5/2 → 6 H 9/2 transitions. The concentration of Sm 3+ ions was optimized to be 0.01 mol% for intense luminescence in GdAl 3 (BO 3 ) 4 :Sm 3+ phosphors. Beyond 0.01 mol% of Sm 3+ ions concentration, luminescence quenching was observed due to energy transfer among the excited Sm 3+ ions through cross-relaxation and dipole-dipole interaction mechanisms. The GdAl 3 (BO 3 ) 4 :0.01 mol% Sm 3+ phosphor was identified as a notable host material to emit intense orange-red luminescence for various solid state lighting devices under 406 nm excitation.

D-π-A conjugated organic dyes made of different donor/acceptor moieties namely Hexylcarbazole (HC), 4,7- Dithiophene-2-yl) benzo[c][1,2,5]thiadiazole (DTBT) and Poly-4-(5-(9-Hexyl-9H-carbazol-2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (PCTB) were prepared by coupling reactions. FTIR, NMR, and mass spectrometry were used to determine the molecular structure of synthesized compounds. Both HC and DTBT show a wide optical transmittance window (400-600 nm) with absorption maxima in the UV region. However, PCTB shows an altered band structure with a broad absorption in the visible domain (448 nm). Density functional theory (DFT) calculations expose that the bandgap between HOMO and LUMO decreases as the conjugation extends, and redshift occurs in UV-Vis absorption spectra. The emission spectrum of PCBT shows strong emission maxima at 541 nm with the corresponding large Stokes shift 3837 cm−1 due to its enhanced charge transfer property in the excited state. Nonlinear optical absorption was studied by open-aperture Z-scan technique using Nd:YAG laser (532 nm, 10 Hz, 9 ns). Here HC, DTBT exhibit a genuine two-photon absorption (TPA) process while PCTB possesses sequential TPA involving excited-state absorption. All dyes exhibit energy-absorbing optical limiting behaviour ascribed due to the two-photon absorption process. Among the investigated dyes, PCTB polymer shows a higher TPA coefficient (1.22 × 10−10 m/W) and a lower onset optical limiting threshold (1.06 × 1012 W/m2). Thus, the tunability of band structure and nonlinearity with a change in the molecular arrangement was successfully demonstrated in thiophene-benzothiadiazole-based organic dyes.

Novel naked eye optical chemosensor containing thiazole ring, namely; (2E,4E)-5-(4-(dimethylylamino)phenyl)-1-(thiazol-2-yl)penta-2,4-dien-1-one, DMAPTP was developed. The solvatochromic response was explored in different solvents of various polarities. The dipole moments in the ground (µg) and excited (µe) states were determined. The large excited state dipole moment demonstrates the excited state's stability in polar solvents. In an ethanolic solution, the sensing response and selectivity of the investigated chemosensor to various metal ions such as Na+, K+, Ca2+, Ba2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Al3+, Hg2+, and Pb2+ were evaluated. The spectral changes suggest that DMAPTP is strongly complexed with the metal ions used. The ground and excited state binding constants, as well as the quenching constants, have been determined. The mechanism of fluorescence quenching was identified as static quenching due to the formation of a non-fluorescent ground state complex using the Stern-Volmer plot. DMAPTP can also be used as a powerful chemosensor, identifying all of the metal ions studied with high sensitivity and selectivity for Fe3+ ions. DMAPTP can serve as a Turn-on-off-on chemosensor, as well as a metallochromic predictor in complexometric titration. This is indicated by the ability of EDTA to decompose the formed complex with the formation of the stable metal-EDTA complex, which leads to fluorescence recovery. The analytical parameters, such as selectivity, sensitivity, and detection limit, were chosen. The fluorescence imaging experiments in living cells demonstrated the biological chemosensing applications of DMAPTP to Fe3+ ions. Furthermore, weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electron microscopy techniques were used to investigate DMAPTP as a corrosion inhibitor for carbon steel in 1.0 M HCl. The collected data reveal that as DMAPTP concentrations increased, its inhibition performance increased as well. On the basis of strong adsorption of inhibitor molecules on the surface of carbon steel and the formation of large protection films, the inhibition efficiencies were determined.

The molecules based on the excited state intramolecular proton transfer (ESIPT) process are widely used in the fluorescent probes, organic light-emitting diodes and other fields due to their unique optical properties. However, the relationship between the structures and optical properties of ESIPT-based molecules still needs to be further explored. Herein, the effects of different functional groups embedded with the benzene ring on the ESIPT properties and electronic spectra of 2-(1H-Benzimidazol-2-yl)phenol (HBYP)-based derivatives (DPYP, HAYP and HIYP) were explored by using the density functional theory and time-dependent density functional theory methods. Utilizing theoretical calculations, the geometric parameters, including bond lengths and bond angles, infrared vibration spectra, frontier molecular orbitals, potential energy curves as well as topological analysis of the bond critical point of the molecules in the ground and excited states were acquired. The results manifest that the ESIPT process is facile to occur for HBYP and its three derivatives upon the photo-excitation, which can be confirmed by comparing the crucial geometric parameters, IR stretching vibration peaks and energy barriers between the S0 and S1 states. It is worth noting that the molecule HAYP exhibits the largest proton transfer barrier at the S1 state among the studied molecules, and the fluorescence peaks corresponding to its enol and keto forms show the most obvious Stokes shifts of 260 nm and 284 nm, respectively. Therefore, we can deduce that the fluorescence properties can be further affected by regulating the ESIPT characteristics of molecules via the functional group substitution.

New near-infrared broad-band emission with λmax~920 nm was detected in 2,5-bis(2′-benzoxazolyl)hydroquinone (BBHQ), a molecule known to undergo the single proton transfer in the ESIPT reaction and to emit the fluorescence with λmax ~600 nm. The new emission was attributed to the fluorescence of the product of double proton transfer in the excited BBHQ. The attribution was based on the qualitative agreement verifying the theoretical predictions and on the behaviour of the two properly chosen derivatives: the diethyl-BBHQ independently showing the same broad-band IR fluorescence, and the monomethoxy-BBHQ, a “negative witness”- a structure with one of two ESIPT reactivity sites eliminated, showing no trace of the new emission.

Aggregation behavior of push-pull salen-type schiff base (BIHyDE) in different solvents at ground and excited state, has been investigated. At ground state, lower energy absorption band is suppressed during concentration dependent UV-Vis study in CHCl3 solution. The broadening of lower energy emission band is observed during concentration dependent fluorescent study in CHCl3 solution. Interestingly, fluorescence life time of BIHyDE in solution is also altered during concentration dependent fluorescence study in CHCl3 solvent. Similar aggregation is also observed at ground and excited state in ACN solvent. Dipolar state and intermolecular dipolar interaction of BIHyDE molecule highly influence towards strong aggregation process and orientation of molecule in solution. Ground state and excited state optical properties are highly influenced by concentration of push-pull salen-type schiff base (BIHyDE) in different solvents.

Two Schiff base ligands (2a and 2b) and their zinc complexes (3a and 3b) have been designed and facilely synthesized through simple condensation reactions using compound 1 derived from natural dehydroabietic acid as the precursor. The larger dihedral angles of the ligands shown by the single crystal X-ray diffraction analysis indicate their stronger molecular motion, which is in consistence with their low fluorescence efficiency that is verified by the photophysical measurements. After coordination with zinc ions, the fluorescence intensity of the zinc complexes is larger, which might be explained by the structural rigidification via coordination, thereby reducing the energy loss from molecular motion. Furthermore, complex 3b exhibits a specific negative solvatochromic effect, and the absorption of its maximum wavelength shows a hypsochromic shift with increased polarity. Such solvatochromic phenomena can be explained by the synergy of intramolecular charge transfer and the proximity effect that may increase the energy difference between the ground state and the excited state in polar solvents. This work not only discusses their relationship between photophysical properties and structures, but also provides a new natural source for further research in fluorescent materials.

The optical absorption and steady-state fluorescence spectra of 4-heptyloxybenzoic acid (4hoba), 4-octyloxybenzoic acid (4ooba) and 4-nonyloxybenzoic acid (4noba) liquid crystals have been measured in a series of different polarity organic solvents. The ground state (μg) and excited state (μe) dipole moments of the monomeric and dimeric 4-alkyloxybenzoic acid liquid crystals have been obtained by means of different solvatochromic shift methods. HOMO-LUMO gaps (HLG) and dipole moments have been tuned by applying external electric (EF) field on monomer, dimer and Au substituted monomer and dimer liquid crystal structures. By applying external electric field, Au substituted monomer liquid crystals display semiconductor character, while Au substituted dimer liquid crystals gain metallic character under E = 0.04 V/A. Eventuated specific and non-specific interactions between solvent and solute in solvent medium have been expounded by using LSER (Linear Solvation Energy Relationships).

In the present work, intermolecular interactions between triphenylphosphine oxide (TPPO) and benzamide (BZM) has been studied in solid state by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques (in solid state and in solution) and by computational modeling (in gaseous phase). Isothermal Titration Calorimetry (ITC) in ethyl acetate solvent showed that complexation is a stepwise process, with 2:1 and 1:1 TPPO/BZM stoichiometries, both driven by entropy. HPLC analysis of isolated single crystal confirmed the existence of a 2:1 TPPO/BZM crystalline complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complexes are relatively weaker than those found in pure precursors. Finally, PALS showed higher positronium formation probability ( I 3 ) at [TPPO 0.62 ·BZM 0.38 ] and [TPPO 0.25 ·BZM 0.75 ] molar fractions, corroborating the existence of two stoichiometries for the TPPO/BZM system and suggesting greater electronic availability of n - and π -electrons in heterosynton complexes, as resulting of interactions, bring forward new evidences of the participation of electronic excited states on the positronium formation mechanism.

Amino acid appended azobenzene hybrid has been synthesized (Fmoc-al-az) and its electronic absorbance and fluorescence spectra were recorded at room temperature in a series of polar and non-polar solvents. The ground state and excited state dipole moments were calculated using solvatochromic shift method. A DFT based study was also performed using- Gaussian09 program package. We have observed that the absorption spectra don't show sensitive behavior to the change in the polarity of the solvent, whereas a bathochromic shift was observed in the fluorescence spectra as we moved from non-polar to polar solvents indicating a π→π* transition. It was observed that the dipole moment in the excited state is much higher than the ground state, due to the amino acid containing hydrogen bond acceptor (O C O) and hydrogen bond donor ( NH) in Fmoc-al-az increasing the reorientation tendency of the solvent molecule around the dye therefore enhancing the stabilization of the excited state which is attributed to the high polarity of the excited states. DFT level electronic structure calculations are also performed for a better molecular level understanding of the experimental observations. We obtained a good correlation between the theoretical studies and experimental results.

An exploration of the photophysical properties of two lophine derivatives with electron-donating groups in the 2-position began with the preparation of compounds 1 and 2 via one-pot reactions in good yields, 83% and 74%, respectively. The absorption spectra of 1 and 2 had bands at approximately 300 nm (e ≈ 25,000–34,000 M−1 cm−1), while that of 2 had an additional band at 348 nm (e = 35,600 M−1 cm−1). These absorptions were assigned to π→π* transitions. Excitation into the absorption band of 1 at approximately 300 nm produced emission at 387 nm, while excitation into either of the absorption bands of 2 produced emission at 406 nm. Of the two compounds, 2 had the higher quantum yield. The emission spectra of compounds 1 and 2 were slightly blue-shifted at 77 K. Excited state lifetimes for 1 and 2 were short (indicating that the observed emission was fluorescence) at room temperature and 77 K, ranging from 1.1 to 1.8 ns. Computational studies of both compounds 1 and 2 were performed to better understand how their structures relate to their photophysical properties.

The fluorescence quenching of fluorenone in protic solvent has been extensively investigated, and the intermolecular hydrogen bond was found to play a crucial role. Unfortunately, the mechanism at atomic level is still not clear. In the present work, we theoretically put forward the charge transfer along the hydrogen bond in the excited states. The vertical excitation energies of the fluorenone-methanol complex as well as the potential energy profiles and surfaces of the vertical excited states and charge transfer states were calculated by using the ab initio electronic-structure methods. The photochemical reactions occurring in the diverse charge transfer states were compared and their decisiveness to the fluorescence quenching was discussed in the paper.

Syntheses of 5-nitro-2-(2-phenylhydrazinyl)pyridine (5-nitro-2-phenylhydrazopyridine), 3-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (3-methyl-5-nitro-2-phenylhydrazopyridine), 4-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (4-methyl-5-nitro-2-phenylhydrazopyridine) and 6-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (6-methyl-5-nitro-2-phenylhydrazo-pyridine) have been described. Electronic absorption and emission spectra of the compounds in the solid state and in various solvents have been measured at room temperature and discussed in terms of DFT quantum chemical calculations. The molecular structures and energy sequences of the singlet and triplet states have been determined in the B3LYP/6-311G(2d,2p) approximations. The Mulliken analysis and non-bonding orbital approach have been used in characterization of the studied compounds. It has been shown that the HOMO-LUMO transition of the studied compounds is observed in the range 23,900 ÷ 29,300 cm −1 and in this excitation the π-electrons of phenyl ring are transferred to nitro group of pyridine ring. In such a transition the hydrazo-bridge should take part as a mediator. The luminescence of the studied hydrazo-compounds is weak, not measureable in the solid state but measureable in solution.

The pyrimidine core is present in a wide variety of compounds that show interesting fluorescent properties and have been used as pigments and dyes. In this research, we synthesized 4-(4-(dimethylamino)phenyl)-6-phenylpyrimidin-2-amine (compound 9) from chalcone (8) with 45% yield. We obtained monocrystals of 9 by slow evaporation of dichloromethane as a solvent. Additionally, we measured the photophysical properties of compound 9, and its absorption wavelength (λabs), molar absorption coefficient (e), excitation wavelength (λexc) and emission wavelength (λem), as well as Stokes shift (Δλ), increase with increasing solvent polarity. These properties are all related to the stabilization of the excited state by the solvent. On the other hand, the quantum yields (Φ values) in toluene and CH2Cl2 were notable greater than those in other solvents due to their high optical density (OD) and the decrease in the loss of fluorescence by non-radiative processes

Carbazole dyes applied in dye-sensitized solar cells (DSSCs) are essential class of organic molecules. Two novel organic dyes DRA-BDC and DTB-BDC including rhodanine-3-acetic acid/thiobarbituric acid as electron acceptors and N, N‑butyl dicarbazole structural as electron donor/spacer have been designed as photosensitizers for DSSCs. Both prepared dyes were characterized by IR, 1H NMR, 13C NMR, mass spectroscopy and CHN analysis. Results of photophysical properties, the UV- Visible spectra of both dyes DRA-BDC and DTB-BDC showed the higher absorption peaks at 440 and 370 nm, respectively. Also, for electrochemical properties, both structures showed more +ve ground state oxidation potential than I−/I − 3, and more –ve excited state oxidation potential than the conduction band edge of the semiconductor. However, the high performance of power-conversion was observed on the DSSCs device with DRA-BDC (η = 1.16%) compared with DTB-BDC dye. Also, DRA-BDC recorded an open circuit voltage (VOC) = 589 mV, short circuit current density (JSC) = 2.46 mA/cm2 and fill factor (FF) = 0.79 under simulated AM 1.5 G irradiation (100 mW/cm2). For the theoretical studies included polarizabilities, optimization geometry, conformational analysis, and photovoltaic analysis based on frontier orbital analysis energy evaluated by using density functional theory model (DFT) with B3LYP/6–311functional basis set.

The results of quantum yield (QY) study of tryptophanyl glutamate (Trp-Glu), tryptophanyl lysine (Trp-Lys) and lysinyl tryptophan (Lys-Trp) dipeptides over the pH range, 1.5 – 13, show that the charge state of the N-terminal amine, and not the nominal molecular charge determines the QY. When the terminal amine is protonated, QY is low (10−2) for all three dipeptides. As the terminal amine cation is found proximal to the indole ring in Trp-Glu and Trp-Lys conformers but not in those for Lys-Trp, its effect may lie only in the partitioning of energy between nonradiative processes, not on QY reduction. QY is also low when both the N-terminal amine and indole amine are deprotonated. These two low QY states can be distinguished by fluorescence lifetime measurement. Molecular dynamics simulation shows that the Chi 1 conformers persist for tens of nanoseconds such that 100 – 101 nanosecond lifetimes may be associated with individual Chi 1 conformers. The ground state electron density or isosurface of high QY (0.30) 3-methyindole has a uniform electron density over the indole ring as do the higher QY Trp dipeptide conformers. This validates the association of ground state isosurfaces with QY. Excited state orbitals from calculated high intensity, low energy absorption transitions are typically centered over the indole ring for higher QY dipeptide species and off the ring in lower QY species. Thus excited state orbitals substantiate the earlier finding that the ground state isosurface charge density pattern on the indole ring can be predictive of QY.

A tetracene dimer linked directly by a single bond has been successfully prepared by using electron withdrawing groups to improve the stability. The molecular structure of this dimer is characterized by 1H NMR, MALDI-TOF mass spectroscopy, and elemental analysis. The minimized molecular structure and X-ray crystallography reveal that the tetracene subunits of this dimer adopt an orthogonal configuration. Its absorption spectrum differs significantly from that of its monomeric counterpart, suggesting the presence of strong interactions between the two tetracene subunits. The excited state of this dimer is delocalized on both two tetracene subunits, which is significantly different from that of orthogonal anthracene dimers, but similar with that observed for orthogonal pentacene dimer. Most of the excited states of this dimer decay by radioactive channels, which is different from the localized twisted charge transfer state (LTCT) channel of anthracene dimers and the singlet fission (SF) channel of pentacene dimers. The results of this research suggest that similar orthogonal configurations caused different propertied for acene dimers with different conjugation length.

Combined quantum-chemical and spectral investigation of cyanine bases derivatives of thiastyryls as well as their analogues with dimethylamino, metoxy and trifluorine-methyl substituents has been fulfilled. The calculations have shown that going from cationic styryl/metoxystyryl to the corresponding neutral bases is accompanied by substantial change of the equilibrium molecular geometry and charge distribution at atoms, while the experimental absorption band undergoes the essential hypsochromic shift. It is established that introducing on the donor groups in the bases causes negligible change of the carbon–carbon bond and atomic charges in the main chromophore, in contrast to the substantial changes of the magnitude and direction state dipole moments in both ground and excited states. It is found that the bases with the donor groups in benzthiazole moiety and with acceptor CF 3 substituent demonstrate the inversion of the direction of the dipole moment. Based on the spectral and quantum-chemical study, one has proposed that some widening of the spectral bands is connected with the vibronic interaction, not with the second electron transition.

A series of alkylamino substituted 2-arylidene and 2,5-diarylidene cyclopentanone compounds were synthesized. Spectroscopic and photophysical properties of these compounds have been measured in a variety of solvents. Absorption and fluorescence maxima have been correlated with the Empirical Scale of Solvent Polarity (E T (30)). Theoretical TD-DFT spectral calculations and Lippert–Mataga analysis support the internal charge transfer (ICT) nature of the S 0 → S 1 excitation for these compounds, with higher degrees of ICT depicted for the alkylamino substituted 2,5-diarylidene cyclopentanones. Photophysical properties consisted of measuring the fluorescence quantum yields (Φ f ) and lifetimes (τ f ) in a variety of solvents. Radiative and nonradiative decay constants have been determined from the Φ f and τ f data. Variation with solvent in the nonradiative rate of decay is interpreted in terms of a competition between internal conversion and intersystem crossing. Lastly, two compounds presented have been shown to undergo excited state protonation in glacial acetic acid.

Studies with density functional theory (DFT) have been done to reinforce our previous experimental findings involving the solvatochromism and the effect of protonation and for three structurally similar donor–acceptor dyes exhibiting intramolecular charge transfer transition. These dyes have similar donor (indole N /amino N ) site and similar carbonyl O as the acceptor centre. The dye with an amino N donor site and indanone O as the acceptor centre has the lowest value of the energy gap between HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) and highest percentage of charge transfer from the N to the O centre. Time dependent density functional theory (TDDFT) has been used to calculate the excitation energy to the lowest singlet excited dipole-allowed states of the dyes. Effect of solvation on excitation energy has been studied by the use of polarisable continuum model (PCM). Computational results indicate that the excitation energy of these dyes is sensitive to solvent polarity and exhibits a red shift as polarity increases. The calculated excitation energies are in good agreement with the values of absorption maximum of these dyes in different solvents obtained in experiment. Studies on protonation of the dyes show that the carbonyl O to be the most favourable site of protonation for all the three dyes. Calculations of linear and first hyperpolarizabilities indicate these dyes to be suitable candidates for possible non-linear optical application.

The excited state proton transfer (ESPT) has been extensively studied for hydroxyarenes, phenols, naphthols, hydroxystilbenes, etc., which undergo large enhancement of acidity upon electronic excitation, thus classified as photoacids. The changes of acidic character in the excited state of cyano-substituted derivatives of phenol, hydroxybiphenyl and naphthol are reviewed in this paper. The acidity constants pK a in the ground state (S 0 ), pK a ∗ in the first singlet excited state (S 1 ) and the change of the acidity constant in the excited state ΔpK a for the discussed compounds are summarized and compared. The results of the acidity studies show, that the “electro-withdrawing” CN group in the molecules of naphthol, hydroxybiphenyl and phenol causes dramatic increase of their acidity in the excited state in comparison to the ground state. This effect is greatest for the cyanonaphthols (the doubly substituted CN derivatives are almost as strong as a mineral acid in the excited state), comparable for cyanobiphenyls, and smaller for phenol derivatives. The increase of acidity enables proton transfer to various organic solvents, and the investigation of ESPT can be extended to a variety of solvents besides water. The results of theoretical investigations were also presented and used for understanding the protolytic equilibria of cyano derivatives of naphthol, hydroxybiphenyl and phenol.

A comparison of excited state and electroluminescent properties between Pt(C^N^N)Cl and Pt(N^C^N)Cl complexes has been done with Time-Dependent Density Functional Theory (TDDFT), [C^N^N = 6-phenyl-2,2-bipyridine, N^C^N = 1,3-di(2-pyridyl)benzene]. The substituent effect of fluorine ligands on eight tridentate cyclometalated Pt(C^N^N)Cl complexes has been investigated, which includes electronic density variation between ground states and excited states, absorption and emission spectra, quantum yields and radiative lifetime. In addition, one dimeric form of Pt(C^N^N)Cl complex has been investigated.

In this work the role of hydrogen bonding in the protonation of 7,8-Benzoquinoline has been investigated using 2,2,2,-trifluoroethanol (TFE): water binary mixture. In our earlier work, protonation of 7,8-BQ was explored in water, TFE and acidic media. It appeared that protonation is significantly promoted in strong hydrogen bonding TFE. However, to substantiate it, a systematic study consisting of TFE: water binary was considered necessary. In this work, we observe that on addition of TFE in water, the intensity of neutral emission gradually decreases while the intensity of emission corresponding to protonated species increases due to faster and enhanced protonation as compared to pure water. Excited state properties of 7,8-BQ upon addition of TFE in water have been discussed using steady state and time resolved fluorescence spectroscopy. Quantum yield and excited state protonation rates have been calculated and discussed. We would like to mention that the present study validates our claim that hydrogen bonding indeed promotes protonation in 7,8-BQ. Besides the importance and applications of excited state proton transfer process in chemistry and biology the work has prospects in studying the conformational changes in proteins.

Textile dyes with high resistance to UV light induced fading on poly (ethylene terephthalate) (PET) fibers are important for textile substrates used in applications such as automobile interiors and outdoor furniture. Dye photostability influenced the development of dye structures for automobile fabrics dating back to the 1980s but the nature of currently used disperse dyes is less widely known. As part of a study designed to provide updates on this subject, the current investigation employed experimental and theoretical methods to determine the nature and properties of commercial dyes used to produce lightfast colors on PET fibers. Having completed the characterization of scarlet and blue disperse dyes for PET-based fabrics used outdoors, our attention turned to the characterization of commercially available lightfast yellow dyes. HPLC analysis showed that a pair of yellow products were mixtures containing three or four dyes, and the use of 1NMR, HRMS and single crystal X-ray diffraction analyses indicated that they were homologous azo–anthraquinone based dyes with or without a 1,8-bis(phenylthio)anthraquinone dye. Results from calculating Frontier HOMO and LUMO isosurfaces indicated strong HOMO/LUMO overlap, and the E0-0 for the homologous anthraquinone-based azo dyes was exactly the same (2.37 eV) which contributes to their photostability.

Terpyridine ligands are the fascinating materials for metal co-ordination. A new fluorescent 4-(3,4-dimethoxyphenyl) terpyridine ligand (DMPTP) was synthesized. We have explored the solvent dependent photophysical characteristics and the metal ion mediated hydrogel formation of DMPTP. The optical behavior of DMPTP is studied by UV–Visible, steady state and time resolved fluorescence measurements in different solvents. DMPTP exhibits structured emission in non-polar hexane solution and broad emission in polar DMSO solution. In addition, DMPTP holds a large solvent dependent fluorescence shift. These results indicate DMPTP undergoes intramolecular charge transfer (ICT) in the excited state. The fluorescence lifetimes also corroborated the ICT behavior of DMPTP. Moreover, DMPTP produces hydrogel upon formation of complex with Cu2+ and Zn2+ in 1:1 ratio. The xerogels of Zn2+ and Cu2+complex exhibit fibrous and flake like morphology, respectively. Interestingly, the hydrogel obtained from Zn2+ complex is highly fluorescent and the one obtained from Cu2+ complex is non-fluorescent.

Complex [Ru(II)L1ClP(Ph3)]Cl (L1= N,N′-bis(benzimidazol-2-yl-ethyl)ethylenediamine) was prepared, and characterized completely by different analytical methods, and its photochemical behavior was studied under visible light. 31P NMR results showed that a light assisted structural transformation in the complex occurred. The formation of different ruthenium complexes was also recorded by LC-MS: [Ru(II)L1DMSO)]2+ (m/z = 563, RT = 19.9 min); [Ru(II)L1DMSO(H2O)]2+ (m/z = 581, RT = 15.69 min); [Ru(II)L1DMSO(H2O) (MeOH)]2+ (m/z = 611, RT = 17.0 min); Ph2P(Cl) = O (m/z = 242, RT = 13.3 min). Theoretical study was used to interpret the structural change. The change of electron density ρ(r) (dipole moment changes from 4.77 to 8.85 D) was observed in benzimidazole group in the excited state, altering the structural parameters of the complex. Furthermore, antibacterial study performed for the complex shows a high toxicity with bacterial cell even at low concentrations (50 μL, 0.5 mM). This is consistent with low cell growth factor with [Ru(II)L1ClP(Ph3)]Cl, established by Atomic Force Microscopy (AFM).

Three new acceptor–donor–acceptor compounds ( LBQ , DBQ , BYQ ) were synthesized and characterized by infrared, hydrogen nuclear magnetic resonance, mass spectrometry and elemental analysis. Their photophysical properties were investigated including linear absorption, single-photon excited fluorescence, fluorescence quantum yield and two-photon absorption. These compounds in CH 2 Cl 2 exhibit good fluorescence quantum yield which are 0.36, 0.26, and 0.25 and the largest two-photon absorption cross-section which are 48, 36, and 181 GM respectively. Under the excitation of Ti: sapphire laser with a pulse width of 140 fs, LBQ and DBQ emit blue two-photon excited fluorescence (TPEF), while BYQ emits bright yellow TPEF. BYQ has a good solubility in water and the σ can be as large as 130 GM, so it shows promising applications in many pharmaceutical and biological fields.

To determine the orbital nature of the excitation for the luminescence of the SbX63−(HDphg)+3 complexes, where X = Cl, Br and HDphg+ is diphenylguanidine, the structure of the valence and core levels was investigated using X-ray photoelectron spectroscopy and density functional theory. The results indicated that the valence bands of the compounds fall into two level systems localised on the anion and cations. HOMO 3a1g2 and LUMO 4t1u on the SbX63− anion, which is responsible for the lower excited state, are antibonding combinations of the Xnpσ group orbitals with Sb 5s and 5p AOs, respectively.

A fluorescent probe 2Z,2′Z-3,3′-(4,4′-methylenebis(4,1-phenylene) bis(azanediyl))bis (1,3-diphenylprop-2-en-1-one) (L) was synthesized and characterized by IR, 1H NMR, ESI-mass, UV–visible and fluorescence spectral techniques. The single crystal analysis illustrates the existence of L in ketamine form. The crystal structure is stabilized by intramolecular and intermolecular hydrogen bonding. The thermal stability of L was studied by TG analysis. The fluorescence spectrum of L shows dual emission, and is due to excited state intramolecular proton transfer (ESIPT) process. This is supported by the high Stokes shift value. Electronic structure calculations of L in the ground and excited state have been carried out using DFT and TD-DFT at B3LYP/6-31G (d,p) level, respectively. The vibrational spectrum was computed at this level and compared with experimental values. Major orbital contributions for the electronic transitions were assigned with the help of TD-DFT. The changes in the Mulliken charge, bond lengths and bond angles between the ground and excited states of the tautomers demonstrate that twisted intramolecular charge transfer (TICT) process occurs along with ESIPT in the excited state.

The new conjugated cruciform chromophores with donor–acceptor character, 1,4-dithienyl-2,5-bis(diphenylamino-phenyl)benzene ( 2 ) and 1,4-bis((5-(E)-2-(5-octylthiophen-2-yl)vinyl)thiophen-2-yl)-2,5-bis(diphenylamno-phenyl)benzene ( 3 ), were synthesized by Suzuki and Stille coupling reaction, respectively. Compounds 2 and 3 provided with a certain crystal character. In addition, compound 2 showed bright green emission in both CH 2 Cl 2 solution and solid film. However, compound 3 showed green emission in CH 2 Cl 2 solution and orange emission in solid film, which was attributed to the intermolecular interaction. The cyclic voltammetry (CV) and density functional theory (DFT) researches indicated that the symmetry crossing branches mainly influenced the lowest unoccupied molecular orbital (LUMO) levels. Moreover, DFT investigation indicated that compound 2 possessed the linear charge transfer pathway, and compound 3 may possess three different types of charge transfer pathways in excited state.

The UV–visible electronic absorption spectra, molar absorptivity, fluorescence spectra, fluorescence quantum yield and excited state lifetime of 1,4-bis [2-(2-pyridyl) vinyl] benzene P2VB were measured in different solvents. The fluorescence quenching of P2VB by molecular oxygen was also studied using lifetime measurements. A 2 × 10−4 mol dm−3 solution of P2VB in dimethyl formamide (DMF) gave amplified spontaneous emission (ASE) in blue spectral region with emission maximum at 420 nm upon pumping by 337.1 nitrogen laser pulse. The photochemical quantum yields (ϕc) of trans–cis photoisomerization of P2VB were calculated in different organic solvents. The photoreactivity of P2VB are also studied PMMA matrix.