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Sulfanilic acid (SAA) has been studied experimentally and theoretically. The DFT approach (Density functional theory) is used for theoretical investigations. Hirshfeld analysis was used for 3D and 2D surface analysis, while NMR (1H NMR and 13C NMR), FT-IR, and UV–Visible spectra were used for spectrochemical study. All of the experimental spectroscopic analyses came back with results that were quite close to the calculated values. To explore electron excitation from occupied to unoccupied orbitals in a single pair of electrons, Hole and Electron density distribution maps (EDD and HDD) were drawn in an excited state with DMSO and MeOH as solvents. The B3LYP method with a 6-311++G(d,p) basis set was utilised to obtain the optimized structure on which all other computations (vibrational frequency, NBO, NHO, NLO, FMO, etc.) are based. The 3D description of intermolecular interactions of crystal surface was done by Hirshfeld surface analysis and while fingerprint plots were used to describe the 2D interactions, SAA was stabilized by formation of H---H/O---H/C---H contacts. VEDA was effectively implemented for total potential energy distribution. The electron localization function was used to examine the Atom-In-Molecule theory (AIM) for determining binding energy, ellipicity, and isosurface projection. The hybridizations of generated bonds, the interference energy, and the interactions between donor and acceptor are all revealed by NBO analysis. The reactive areas of the molecule were defined using Fukui functions and the molecular electrostatic potential (MEP). Charge transfer was revealed in the UV–Vis spectrum, which was computed using TD-DFT/PCM methods with various solvents. At various temperatures, thermodynamic parameters such as free energy, enthalpy, and entropy were calculated. By calculating the electrophilicity index, the bioactive probability of the molecule was theoretically proven. Molecular docking was used to explore protein-ligand interactions, and the lowest binding energy was found to be −6.4 kcal/mol. SAA was also subjected to drug-likeness investigation including its derivatives and all compounds were discovered to have a similar nature. As a result, this molecule could be utilized in the development of drugs.

Three new fluorescent o-hydroxyaryl Schiff base derivatives are synthesized and their structures are characterized by NMR and FTIR spectroscopies. In this study, the solvent effect on the absorption and fluorescence spectral properties, Catalan and Taft-Kamlet solvatochromism models, and electric dipole moments in the ground and excited states, are investigated for synthesized compounds. Specific and non-specific solute–solvent interactions are investigated using Catalan and Taft-Kamlet solvatochromism models in various solvents with different polarities. Taft-Kamlet and Catalan solvatochromism models derived for absorption spectra indicate that solvent dipolarity/polarizability (π*) and solvent polarity (SP) are dominant in controlling absorption spectral shifts. As a result of solute–solvent interactions, absorption spectra exhibit positive solvatochromism, while fluorescence spectra show negative solvatochromism with the increase of solvent polarity. The ground state dipole moment is determined using the Bilot–Kawski method, and the excited state dipole moment is calculated using the Bilot–Kawski, Lippert–Mataga, Bakhshiev, modified Bilot-Kawski and Reichardt correlation methods. The dipole moments estimated in both ground and excited states confirm that Schiff base compounds are more polar in the excited state. The frontier molecular orbitals (HOMO and LUMO), molecular electrostatic potential (MEP), density of states (DOS) and solvent accessibility surfaces (SAS) of these compounds have been calculated using the DFT/B3LYP/6-311++G(d,p) level of theory.

Considering the worth of molecular designing, A-D-A type four small donor (SM1-SM4) photoactive materials comprised of DTS core, substituted with push-pull acceptors at terminal sites linked through bithiophene units were investigated. In present project, detailed theoretical consideration under DFT and TD-DFT methods (CAM functional/basis set 6-31G) was given-to explore wavelength dependent (absorption maxima, first excitation energy, light harvesting efficiency), electronic (FMO, DOS, TDM), reactivity (IP, EA, MEP), and charge transfer parameters (Voc, FF) of selected molecules (SM1-SM4) in systematic way. All novel molecules revealed broadening of absorption maxima and lessening of band gaps comparative to absorption coefficient and energy difference between HOMO/LUMO of RM due to electron pulling nature of acceptor groups. Greater dipole moment of all designed chromophores in excited state suggests their good solubility in solvent medium (chloroform) as compared to gaseous medium. Furthermore, charge transfer dynamics in terms of internal hole and electron reorganization energies give lower values which indicate higher transfer abilities for SM2 and SM1 respectively. Excellent output results for modelled molecules interpreted through open circuit voltage (with PC61BM) and fill factor, predict rise in PCE value than already reported molecule. Out of class, SM4 molecule emerged as an ideal photovoltaic material on account of better optical properties, easy electronic transitions, enhanced chemical reactivity, fast charge conductivity, and high estimated PCE. Eventually, these encouraging results favors the structural modeling of small molecules achieved through effective combination of end-capped moieties. We look forward that this entire work may provide strong theoretical guidelines, aids in designing and amplifying the optoelectronic features of proposed frameworks on vast scale than reference.

In this work, the hydrogen bond effect on excited state mechanism of 2-isopropyl thioxanthone has been investigated in protic solvents by spectroscopic and computational chemistry methods. The two models of single hydrogen bond and double hydrogen bond provide the basis for the photophysical properties of ITX-solvent complexes, and the study of excited state hydrogen bond provides a theoretical basis for the emission of singlet and triplet states of ITX. We demonstrated that the intermolecular hydrogen bond C O⋯H O between ITX and protic solvents are significantly strengthened in the electronically excited-state upon photoexcitation of the ITX hydrogen-bonded complexes. Interestingly, hydrogen bonding inhibits molecular vibration and eliminates self-quenching and atmospheric oxygen quenching, which effectively inhibits non-radiative processes and improves the efficiency of emission. All the calculated spectral features are in good agreement with the spectral results recorded in experiments. This demonstrates that the ground state and excited state of the hydrogen-bonded ITX complexes presented here can well delineate in different solvents. This work provides a theoretical basis for the further development of the application of thioxanthone compounds.

This study reported on a variety of target phenanthridine dyes carrying hydroxy groups that were employed as near-IR two-photon absorption (TPA) photostabilizers for polymers. It was demonstrated that the target phenanthridine dyes underwent reversible excited state proton transfer (ESPT) in strong polar protic and aprotic solvents, such as ethanol, which was more remarkable under near-IR two-photon excitation. It was determined that the target dyes processed regular molecular stacking in mixed organic solvents/H2O solvents (such as ethanol/H2O, 90% water volume). The orderly molecular aggregation of the target phenanthridine dyes intensified the reversible ESPT emission under one-photon and near-IR two-photon excitation, respectively. Hence, the absorbed energy was consumed by the reversible ESPT process of the target dyes. As a consequence, the target dyes were evaluated as near-IR TPA photostabilizers for polymers. In contrast, the reference phenanthridine dyes lacking of hydroxy groups did not exhibit ESPT or photostability under light irradiation.

In this paper, we have designed and synthesized HBT-fused aryl-imidazole derivatives HBTA, HBTB, HBTC and HBTD through π-expanded system, which have large absorption extinction coefficients, relatively high quantum yields, large Stokes shifts. The dyes HBTB, HBTC and HBTD still retained excited state intramolecular proton-transfer property (E* and K* emission). They also exhibited good ESIPT properties in serum. The experimental results and theoretical calculations verified that the nonplanar and nitrogen heterocyclic structure of π-expanded rings was beneficial for the k* emission under the same conditions. Moreover, The HBTA, HBTB, HBTC and HBTD were successfully applied for the imaging in living cells and zebrafish.

In this work, we investigated the fluorescence mechanism of the probe (E)-3-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2,3-dihydrothiophene-2-carboxamide (DHADC) for both Zn2+ and CN− by using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods. Utilizing the constructed potential energy curves both in the ground and excited states as a function of the distance of N2···H1, the proton transfer process of DHADC has been explored. According to the calculated spectra, another more reasonable structure of DHADC-CN for the product of DHADC responding to CN− has been proposed. All of the simulated absorption and emission spectra in this work are in agreement well with those in the experiment. Furthermore, the excited state decay picture and the fluorescence quenching mechanism of DHADC, as well as the fluorescence mechanism for Zn2+ and CN− have been fully explored.

Four liquid crystalline molecules in the homologus series of 5,5′-Bis-(alkylpyridinyl)-2,2′-bithiophenes (nPBTP with n = 7, 8, 10, 12) have been investigated for UV sensing mechanism. Optimization of these compounds has been carried out through hybrid functional B3LYP along with 6-31 + G (d) basis set based on the crystallographic parameters as input. The UV absorption spectra of the molecules have been calculated and the configuration interaction singles (CIS) approach has been employed to study the electronic transitions features along with excited states calculation with the help of semiempirical Hamiltonian ZINDO. The INDO/S + CI method has been implemented for the same for comparison of the results. Various spectral parameters associated have been reported. The HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies estimations, and the transition energies, the electron excitation nature concerning on the structural variations in the molecules are clarified. The results obtained suggest model UV sensing mechanism for full colour display applications. A comparison has been made between nematic and smectic systems.

2-(2-Furyl)-3-hydroxychromone (FHC) is a dual emitter fluorescent probe exhibiting excited state intramolecular proton transfer (ESIPT) reaction in solution and inserted in biological relevant macromolecules. Its two fluorescence bands are attributed to normal form (N*) for the short wavelength and the long-wavelength band to the tautomer form (T*), the product of the ESIPT reaction. To rationalise the mechanisms that lead to the occurrence of the ESIPT reaction and predict the fluorescence spectra, the excited and ground state dynamic of this compound was followed in acetonitrile, ethanol, methanol, N-methylformamide and formamide, by the classical molecular dynamic simulation in conjunction with the empirical valence bond (EVB) model to describe bond dissociation process. A set of transferable parameters were used to fit the EVB potential energy curve to TDDFT data. Using these parameters, the occurrence time of the ESIPT reaction was predicted to be 7, 84, 113, 98, 207ps, respectively in the considered solvents, in excellent agreement with the experimentally reported values. These values are comparatively higher than those determined for the parent flavone dye (less than 100 fs), giving FHC a higher potential for sensor development. By examining structural parameters such as the distance from the proton to acceptor, the intermolecular H-bond between FHC and the solvent molecules and proton trajectories, we found that ESIPT occured in acetonitrile and alcohols as a combination of low frequency high amplitude donor-acceptor bending motion and charge redistribution in the excited state, that were modulated by the solvent H-bond donor potency. Differently in amides ESIPT occured via tunnelling mechanism due to the close energy of N* and T*. Fluorescence spectra calculated from potential energies of the EVB model along the reaction coordinates were qualitatively in agreement with the recorded spectra.

The paper analyzes the electronic-vibrational states of six possible conformers of the dye oxazine 1 (also known as oxazine 725) in an aqueous solution using the SMD solvent model and the 6-31++G(d,p) basis set. Vibronic absorption spectra are calculated using a wide range of hybrid functionals. The X3LYP functional gives the best agreement with the experiment for the positions of the main maximum and shoulder. According to the calculations, the shoulder in the experimental spectrum is of vibronic origin. Various characteristics of the ground and excited states (Duschinsky matrices, IR spectra, atomic charges, dipole moments, maps of the distribution of the electrostatic potential) were obtained. All six investigated conformers have similar vibronic absorption spectra and frontier molecular orbitals. Significant differences between them are observed only for the set of vibronic transitions and relaxation from nonequilibrium to an equilibrium excited state. The effect of two strongly bound water molecules on the excitation of the dye was analyzed.

Studies have shown that changing the substituted groups applied to the amine can effectively affect the strength of the excited state hydrogen bond. However, it is not common to study the mechanism of how to effectively control the hydrogen bond strength of the excited state through the substituted group. Here, we have taken 7-Aminoquinoline and its various derivatives, the TDDFT method is used to study the influence of its R substitution on the hydrogen bond strength of the excited state and the mechanism of solvent-assisted excited-state multiple proton transfer (ESMPT) reaction. We have utilized bond length, IR vibrational spectra, atomic polar tensors (APT) charge analysis and potential energy curves to depict the relationship between hydrogen bond strength and substituted groups in excited state. We have modulated deliberately the number of methanol molecules involved in the ESMPT processes based on the site-specificity of hydrogen-bonding interactions, the potential energy curves indicate that the proton transfer process is more likely to happen in 7AQs·(MeOH)3 tetramer than in 7AQs·(MeOH)2 trimer, which is conflict with previous experimental conclusion. Meanwhile, the transition state structure during the ESMPT reaction indicates that the process is concerted. Our study demonstrates well the fluorescence behavior of 7AQs molecules regulated by different R substituents and extends the boundaries of site-specific hydrogen-bonding interactions research slightly.

In this work, we studied by means of density functional theory (DFT) and time-dependent DFT(TD-DFT) using the effect of the mixture composition C4mimBF4/acetonitrile on the charge transfer in Coumarin 153(C153) after photoexcitation. The mixture composition was characterize by their corresponding static dielectric constant e m . The PBE0 and M06-2X functionals combined with linear response (LR) and state specific (SS) solvation schemes were used to obtain various electronic properties of C153 in both ground and excited states. Our results show that the calculated fluorescence Stoke shift, using the state specific solvation scheme correlates well with the corresponding experimental data obtained for C153 dissolved in other solvents have the same static dielectric constant as of the C4mimBF4/acetonitrile mixture. The charge transfer was quantified using descriptors such as charge qCT, distance dCT, and the dipole moment μCT between the ground and the excited state. These descriptors were calculated based on four different partial atomic charge models, namely Mulliken, Natural Populations Analysis, Hirshfeld, and Merz–Kollman. The charge transfer also was quantified using descriptors based on the electrostatic surface potential namely the polarity index. Both PBE0 and M06-2X functionals combined with the Linear Response solvation scheme result in a systematic increase of the qCT, dCT, and μCT with increasing e m , while they decrease for most of the partial atomic charge models when the State Specific solvation scheme is used. This later result points out that this solvation scheme is not suitable for the description of the excited state of C153 in this mixture. Our results show that the extent of change of these descriptors is small and indicates that the effect of the mixture composition on the charge transfer in C153 is weak.

Encapsulation of 4-hydroxy coumarin (4HC) within the p-sulfonatothiacalix[4]arene has been investigated employing the steady state fluorescence, 1H NMR titration experiments combined with ωB97x-D based density function theory. Theoretical calculations have shown that in the 4HC⊂TSCX4 complex the guest encapsulates partially within the cavity of the macrocycle via CH⋅⋅⋅π interactions while the lactone ring excludes the cavity binds to sulfonate portals of the host by hydrogen bonding interactions. Natural transition orbital analyses were used to assign electronic transitions in 4HC⊂TSCX4 complex and its 7HC analogue. The first allowed vertical excitation at 266 nm in the complex arises from a transfer of electron density on the lactone ring of 4HC to aromatic ring of the macrocycle. Further the C=O vibration at 1791 cm−1 in the infrared spectra of 4HC downshifts to 1724 cm−1 upon complexation with the TSCX4. The noncovalent interactions reduced density gradient method was employed to characterize non-bonding interactions in the complex in conjunction with quantum theory of atoms in molecules. Steady state fluorescence measurements reveal that addition of TSCX4 in DMSO to 4HC results in quenching of the 397 nm band. Furthermore, the Stern-Volmer quenching constant of the complex determined to be Ksv = 2.19 × 104 M−1 has static and the upward curvature concave towards the I0/I axis in Stern-Volmer plots thus was noticed. The recorded excited state lifetime of complex led to the bimolecular quenching constant kq to be 1.98 × 104 M−1 s-1. Upon complexation the hydroxyl protons (Hb) in 4HC engender large deshielding as opposed to aromatic protons of TSCX4 macrocycle which emerge with up-field signals in the measured 1H NMR spectra. The noncovalent binding manifests in NOESY spectrum of the 4HC⊂TSCX4 complex. The association constant of the complex obtained from the UV–Vis and steady state fluorescence correlate well with those from 1H NMR titration experiments which establish that the inclusion complex is stable.

In this article we have investigated the solvation, rotational dynamics and photo physics of diketone derivatives DK-2 and DK-3 in alcohols and alkanes at room temperature through both a time-resolved fluorescence depolarization technique and steady state. Viscosity of dissolvable varies linearly with respect to rotational times of the molecule. Outcomes are investigated by utilizing the theory of hydrodynamic (SED) Stokes- Einstein-Debye to evaluate the friction with stick and slip limiting conditions. In addition, using the solvatochromic shift and quantum chemical technique aromatic di-ketone derivatives, 1-(4′-dodecyl-[1,1′-biphenyl]-4-yl)-3-(4-ethoxyphenyl) propane-1,3-dione (DK-2) and 1-(4′-dodecyl-[1,1′-biphenyl]-4-yl)-3-(4-(nonyloxy)phenyl)propane-1,3-dione (DK-3) estimated properties of fluorescence. The excitation and emission spectra of DK-2 and DK-3 have been observed in several solvents. The dipole moments calculated using DFT theory and solvatochromic correlations. Estimated (μg) value by DFT theory is relatively greater than the solvatochromic shift techniques. The dipole moments of excited state (μe) are found to be more prominent than dipole moment of ground states (μg) which approves π → π* transition. The variance of dipole moments (Δμ) was determined from microscopic solvent polarity parameter (ETN) and solvatochromic shift technique and outcomes are compared.

The photophysical and photochemical properties of the novel sensor 3-(cyanooxy)-hydroxyflavone (FLVN-OCN) and 3-hydroxyflavone (HPO) generated by the reaction with hydrogen sulfide (H2S) have been investigated theoretically. Analysis of structure parameters and infrared vibrational spectra indicate that hydrogen bond is strengthened in the first (S1) excited state, which is beneficial to the excited-state intramolecular proton transfer (ESIPT). The strength of hydrogen bond is determined by the reduced density gradient model. The calculated absorption and emission spectra of the tautomer (HPO-PT) are located at 412.5 and 536.8 nm, respectively, which are in good agreement with the experimental values (425 and 525 nm). The results show that the measured spectra experimentally are ascribed to HPO-PT configuration. Combined with the frontier molecular orbital and hole-electron analysis, the electron density of the product HPO transfers from the oxygen atom on the hydroxyl group to the adjacent oxygen atom, which affects the fluorescence properties, resulting in significant fluorescent changes with the addition of H2S. The obtained energy barrier of the S1 state (4.22 kcal/mol) is lower than that of the ground (S0) state (14.58 kcal/mol) through the potential energy curves (PECs) of HPO, which further indicates that the ESIPT process is more likely to occur in the S1 state. The work explains the detection mechanism for H2S of the fluorescent probe FLVN-OCN and provides a reference for the further study of this probe.

The solvatochromic effect of solvents on the absorption and fluorescence spectra of three carbocyanine dyes, namely 1,1′,3,3,3′,3′-hexamethylindocarbocyanine chloride (HIC); 1,1′,3,3,3′,3′-hexamethylindodicarbocyanine iodide (HIDC); and 3,3′-diethyloxadicarbocyanine iodide (DODC), have been investigated. The experimental ground and excited-state dipole moments of the dyes have been estimated via the well-known models by Lippert-Mataga, Bakhshiev, Kawski-Chamma-Viallet, and the Dimroth-Reichardt’s empirical model. The influence of the solvation effect on the luminescence quantum yields was also examined and a strong correlation between the luminescence quantum yield values and the solvent viscosity was established. The fluorescence signal enhancement sensitivities between dyes were compared based on the Forster-Hoffmann equation. DFT and TDDFT calculations at the CAM-B3LYP/6-31G(d,p) level of theory were performed for the analysis of the nature of the electron transitions in absorption and excitation processes. Six phases different in polarity were considered during these computations, namely the gas, toluene, chloroform, acetone, methanol, and water. Transition electron density plots, Mulliken atomic partial charges, and Mayer bond orders were used for the analysis of the redistribution of electron density upon excitation. The specific behavior of the dyes in the glycerol medium was interpreted via the analysis of non-covalent interactions between the dye and glycerol molecules in terms of the reduced density gradient method.

In this work, we examined the ground and low-lying excited states of six dipyridyl isomers (2,2′-dipyridyl, 2,3′-dipyridyl, 2,4′-dipyridyl, 3,3′-dipyridyl, 3,4′-dipyridyl, and 4,4′-dipyridyl), emphasizing the effects that solvation (water) molecules have on properties such as ground state equilibrium structures, relative energies in terms of conformations and transition states (regarding possible cis–trans interconversions), vertical excitation energies (VEs), generalized oscillator strengths (GOS), and excited state structures. Density functional theory (DFT) and its time-dependent formalism (TD-DFT) were used for determining all the ground state and excited state properties, respectively, both being employed with the CAM-B3LYP exchange–correlation functional and the cc-pVTZ basis set. In addition, effects caused by interactions with the solvent environment were probed by means of using two different approaches: i) the integral equation formalism polarizable continuum model (IEF-PCM) and ii) a composite solvation model (CSM) through the incorporation of explicit water molecules in combination with the IEF-PCM. In general, a decrease in the relative energies regarding a given cis/trans counterpart is noticed when solvation is considered independently from the model used; all the dipyridyl cis/trans isomers became (practically) isoenergetical due to dipyridyl-H2O hydrogen-bonding interactions. Moreover, the interconversion barriers were also found to be lowered due to solvation effects. For instance, the energy barrier in terms of interconversion of the trans 2,2′-dipyridyl to the cis 2,2′-dipyridyl was determined as (approximately) 67 % of the corresponding value obtained in the gas-phase. Although no major differences regarding the values of the VEs associated to a bright state are suggested from the comparison between the results obtained for a given isomer through the consideration of solvation and those corresponding determined in the gas-phase, the GOS are all increased when solvation is considered, suggesting an enhancement in the photoabsorption of all the isomers when in presence of solvent. In addition and in contrast to what was seen previously in the case of the gas-phase, 4,4′-dipyridyl presented a bright state among the five lowest-lying excited singlets (accessible at the UVC energy region), which is located at 5.49 eV (with GOS = 0.4465) at the TD-DFT/CAM-B3LYP/cc-pVTZ level of theory in water (IEF-PCM) and at 5.47 eV (with GOS = 0.5331) at the same level of theory with the CSM. Given that no significant change was noticed in the optimized structures for the excited states, it is possible to infer that all the compounds will decompose through photo decomposition (chemical reaction occurring in the excited state) rather than direct photolysis when in solution.