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Positron emission tomography (PET)-fluorescence imaging is an emerging field of multimodality imaging seeking to attain synergy between the two techniques. The probes employed in PET-fluorescence imaging incorporate both a fluorophore and radioisotope which enable complementary information to be obtained from both imaging techniques via the administration of a single agent. Fluorine-18 is the most commonly used radioisotope in PET imaging and consequently many novel attempts to radiofluorinate various fluorophores have transpired over the past decade. In this Minireview, the most relevant fluorine-18 labelled PET-fluorescence probes have been classified into four groups as per the implemented fluorophore: 1) boron-dipyrromethene (BODIPY) dyes, 2) cyanine dyes, 3) alternative organic fluorophores and 4) organometallics, such as quantum dots (QDs) and rhenium complexes. The biological, radiochemical and photophysical properties of each probe have been systematically compared to aid future endeavours in PET-fluorescence chemistry., (© 2020 Wiley-VCH GmbH.)

A novel second-generation blue fluorescent polyamidoamine dendrimer peripherally modified with sixteen 4-N,N-dimethylaninoethyloxy-1,8-naphthalimide units was synthesized. Its basic photophysical characteristics were investigated in organic solvents of different polarity. It was found that in these solvents, the dendrimer is colorless and emitted blue fluorescence with different intensities depending on their polarity. The effect of the pH of the medium on the fluorescence intensity was investigated and it was found that in the acidic medium, the fluorescence is intense and is quenched in the alkaline medium. The ability of the dendrimer to detect metal ions (Pb2+, Zn2+, Mg2+, Sn2+, Ba2+, Ni2+, Sn2+, Mn2+, Co2+, Fe3+, and Al3+) was also investigated, and it was found that in the presence of Fe3+, the fluorescent intensity was amplified more than 66 times. The antimicrobial activity of the new compound has been tested in vitro against Gram-positive B. cereus and Gram-negative P. aeruginosa. The tests were performed in the dark and after irradiation with visible light. The antimicrobial activity of the compound enhanced after light irradiation and B. cereus was found slightly more sensitive than P. aeruginosa. The increase in antimicrobial activity after light irradiation is due to the generation of singlet oxygen particles, which attack bacterial cell membranes. [ABSTRACT FROM AUTHOR]

Open-shell molecules rarely fluoresce, due to their typically faster non-radiative relaxation rates compared to closed-shell ones. Even rarer is the fluorescence from states that have two more unpaired electrons than the open-shell ground state, since they involve excitations from closed-shell orbitals to vacant-shell orbitals, which are typically higher in energy compared to excitations from or out of open-shell orbitals. States that are dominated by the former type of excitations are known as tripdoublet states when they can be described as a triplet excitation antiferromagnetically coupled to a doublet state, and their description by unrestricted single-reference methods (e.g., U-TDDFT) is notoriously inaccurate due to large spin contamination. In this work, we applied our spin-adapted TDDFT method, X-TDDFT, and the efficient and accurate static-dynamic-static second order perturbation theory (SDSPT2), to the study of the excited states as well as their relaxation pathways of copper(II) porphyrin; previous experimental works suggested that the photoluminescence of some substituted copper(II) porphyrins originate from a tripdoublet state, formed by a triplet ligand π → π* excitation antiferromagnetically coupled with the unpaired d electron. Our results demonstrated favorable agreement between the X-TDDFT, SDSPT2 and experimental excitation energies, and revealed noticeable improvements of X-TDDFT compared to U-TDDFT, not only for vertical excitation energies but also for adiabatic energy differences. These suggest that X-TDDFT is a reliable tool for the study of tripdoublet state fluorescence. Intriguingly, we showed that the aforementioned tripdoublet state is only slightly above the lowest doublet excited state and lies only slightly higher than the lowest quartet state, which suggests that the tripdoublet of copper(II) porphyrin is long-lived enough to fluoresce due to a lack of efficient non-radiative relaxation pathways; an explanation for this unusual state ordering is given. Indeed, thermal vibration correlation function (TVCF)-based calculations of internal conversion, intersystem crossing, and radiative transition rates confirm that copper(II) porphyrin emits thermally activated delayed fluorescence (TADF) and a small amount of phosphorescence at low temperature (83 K), in accordance with experiment. The present contribution is concluded by a few possible approaches of designing new molecules that fluoresce from tripdoublet states.

The target mono‐BF2 complex is weakly emissive in fluid solution because radiationless decay of the excited‐singlet state is promoted through an intramolecular N⋅⋅⋅H−N hydrogen bond. The lack of mirror symmetry for this compound is attributed to vibronic effects, as reported previously for the bis‐BF2 complex (BOPHY). Red‐shifted fluorescence is observed from single crystals, the emission quantum yield approaching 30 % with a fluorescence lifetime of 2 ns. The large Stokes shift of 5,700 cm−1 helps minimize self‐absorption. Crystallography indicates that the internal fold and twist angles are increased substantially in the crystal, but the hydrogen bond is weakened relative to solution. The crystal structure is compiled from pairs of head‐to‐tail molecules having a shift of ca. 4.1 Å and closest approach of ca. 3.5 Å. These molecular pairs are arranged in columns, which, in turn, assemble into sheets. The proximity favors excitonic coupling between individual molecules, with the coupling strength obtained by analysis of the absorption spectrum reaching ca. 1,000 cm−1. Both the ideal dipole approximation and the extended dipole methodology seriously overestimate the coupling strength, but the atomic transition charge density procedure leads to good agreement with experiment. Emission is attributed to the closely coupled molecular pair functioning in an excimer‐like manner with the exciton trapped in a local minimum. Increasing temperature causes a slight blue shift and loss of fluorescence. [ABSTRACT FROM AUTHOR]

The development of dual‐state emissive (DSE) fluorophores, i. e. organic molecules showing balanced emission in both solution and as molecular solids, has recently become an emerging approach in material science, biology, sensing, and optoelectronics. However, the majority of existing DSE fluorophores represents structural modifications of the scaffolds known for their aggregation‐induced emission (AIE) properties, e. g. tetraphenylethylenes (TFE), triphenylamines (TFA), and others. In this study, we introduce aurones as an easily accessible scaffold for the construction of DSE fluorophores and describe the main design principles allowing to achieve the balanced emission in both solution and solid state. Herein, we present the solid‐state fluorescence in a systematic series of aurone derivatives for the first time. We propose that the newly found DSE properties of aurones in combination with their established biological activity can be applied efficiently in biomedical studies and diagnostic tools. [ABSTRACT FROM AUTHOR]

Extensive use of pesticides in agriculture can lead to environmental pollution and potentially adverse health effects. A fluorescence Turn‐On molecular switch, derived from naturally occurring α‐mangostin (MN), isolated from the pericarp of mangosteen fruit and Graphene Quantum Dots (GQDs) synthesized from honey, was developed for the detection of carbofuran‐an organic toxic carbamate pesticide. GQDs derived from honey shows a strong fluorescence emission centered at 430 nm, which was efficiently quenched by the addition of MN. The quenching of fluorescence of GQDs by the addition of MN (OFF state) and the regaining of quenched fluorescence of GQDs‐MN system (ON state) upon the addition of the pesticide carbofuran was utilized as a detection strategy for the toxic pesticide carbofuran. [ABSTRACT FROM AUTHOR]

The mechanism behind reverse intersystem crossing (rISC) in metal‐based TADF emitters is still under debate. Thermal rISC necessitates small singlet/triplet energy gaps as realized in donor‐acceptor systems with charge‐transfer excited states. However, their associated spin‐orbit couplings are too small to account for effective rISC. Here, we report the first nonadiabatic dynamics simulation of the rISC process in a carbene‐copper(I)‐carbazolyl TADF emitter. Efficient rISC on a picosecond time scale is demonstrated for an initial triplet minimum geometry that exhibits a perpendicular orientation of the ligands. The dynamics involves an intermediate higher‐lying triplet state of metal‐to‐ligand charge transfer character (3MLCT), which enables large spin‐orbit couplings with the lowest singlet charge transfer state. The mechanism is completed in the S1 state, where the complex can return to a co‐planar coordination geometry that presents high fluorescence efficiency. [ABSTRACT FROM AUTHOR]

Multistimuli‐responsive chromism was observed for vinylene‐linked bisflavin 1 a with an extended π‐conjugated platform. The yellow emission of a dilute solution of 1 a in CHCl3 (0.2 mM) observed at 298 K under UV excitation was changed to orange or red emission upon (1) an increase of concentration, (2) a decrease of temperature, and (3) variation of the solvent. This is in contrast to the almost non stimuli‐responsive chromism of the N‐methylated bisflavin analogue 1 b and monoflavin 2 a. Mechanistic investigation by 1H NMR analysis under various conditions revealed that the extended π‐conjugation platform and imide moiety of 1 a generate controllability in the formation of lower‐ and higher‐ordered aggregates, which induce variation of the emission color upon change. Bisflavin 1 a also exhibited redox‐induced chromism, where the orange emission of 1 a was quenched by the addition of hydrazine under anaerobic conditions, and changed back to the original emission upon subsequent bubbling of O2 gas. [ABSTRACT FROM AUTHOR]

Marine Coelenterazine is one of the most well-known chemi-/bioluminescent systems, and in which reaction the chemi-/bioluminophore (Coelenteramide) is generated and chemiexcited to singlet excited states (leading to light emission). Recent studies have shown that the bromination of compounds associated with the marine Coelenterazine system can provide them with new properties, such as anticancer activity and enhanced emission. Given this, our objective is to characterize the photophysical properties of a previously reported brominated Coelenteramide analog, by employing a combined experimental and theoretical approach. To better analyze the potential halogen effect, we have also synthesized and characterized, for the first time, two new fluorinated and chlorinated Coelenteramide analogs. These compounds show similar emission spectra in aqueous solution, but with different fluorescence quantum yields, in a trend that can be correlated with the heavy-atom effect (F > Cl > Br). A blue shift in emission in other solvents is also verified with the F–Cl–Br trend. More relevantly, the fluorescence quantum yield of the brominated analog is particularly sensitive to changes in solvent, which indicates that this compound has potential use as a microenvironment fluorescence probe. Theoretical calculations indicate that the observed excited state transitions result from local excitations involving the pyrazine ring. The obtained information should be useful for the further exploration of halogenated Coelenteramides and their luminescent properties. [ABSTRACT FROM AUTHOR]

For the present work, solvent (toluene, o- xylene, chloroform, chlorobenzene, and 1,2-dichloroethane) and concentration-dependent (∼10−6–10−3 g ml−1) photophysical properties of poly(9,9-di-(2-ethylhexyl)-9-H-fluorene-2,7-vinylene) (PEFV) were investigated in detail in liquid media as well as thin films. Also, temperature-dependent (3–60 oC) fluorescence emission measurements of PEFV were conducted in liquid media. The steady-state and time-resolved data indicate the existence of weak interchain interaction in liquid media at high concentration. However, both ground-state aggregation and interchain interaction are present for PEFV in thin film. The interchain interaction plays a dominant role on the fluorescence emission of PEFV in thin film on the red side of the spectra. Graphical Abstract [ABSTRACT FROM AUTHOR]

Rhodamine B (R h B) is widely used for its high fluorescent quantum yield and strong absorption in the visible range of the spectrum; however, its facile aggregation in aqueous solutions dramatically affects its photophysical properties. Surprisingly, the excited state dynamics of rhodamines are not fully understood despite the extensive literature around them. Here, we present a complete picture of the photophysics of R h B and the most likely dimer formed in aqueous solution. We deconvolved the excited state dynamics of R h B and its non-covalent dimer using a combination of steady-state (SS) and time-resolved spectroscopic methods supported by density functional theory (DFT) and time-dependent DFT (TD-DFT). In particular, we have determined the dimerization equilibria constant in sodium perchlorate solutions and measured the dimer's photo-induced charge separation and charge-recombination events. Additionally, we studied 12 DFT exchange–correlation functionals (XCF), and determined which are appropriate and which are not appropriate for studying and interpreting the excited state dynamics observed through femtosecond transient absorption (fsTA). [Display omitted] • Rhodamine B, a popular fluorescent dye, is known to dimerize in aqueous solutions. • The dimer's absorption spectrum indicates that is a face-to-face "H" aggregate. • After absorbing light, the dimer undergoes electron transfer to create a charge-separated state. • The dimer's excited-state lifetime is 284 ps compared to the monomer's ̃1500 ps. • Relaxation of the dimer's exciton-coupled states is observed in 50 fs. [ABSTRACT FROM AUTHOR]

Carbazole is a unique template associated with several biological activities. It is due to the diverse and versatile biological properties of carbazole derivatives that they are of immense interest to the research community. 1-keto-1,2,3,4-tetrahydrocarbazoles are important synthetic intermediates to obtain carbazole derivatives. Several members of this family emit fluorescence on photoexcitation. In the context of biochemical and biophysical research, designing and characterising small molecule environment sensitive fluorophores is extremely significant. This article aims to be a state of the art review with synthetic and photophysical details of a variety of fluorophores based on 1-keto-1,2,3,4-tetrahydrocarbazole skeleton. [ABSTRACT FROM AUTHOR]

Dual emission light‐emitting dendrimers composed of phosphorescent fac‐tris[2‐phenylpyridyl]iridium(III) [Ir(ppy)3] cores and thermally activated delayed fluorescence‐based (TADF‐based) dendrons have been prepared. The TADF‐based dendrons are designed to have green or blue emission. The dendrimers show solvatochromism, with the emission switching between phosphorescence and TADF depending on the medium in which the measurement is undertaken. Time‐dependent photoluminescence (PL) spectra measurements show that the TADF dendrons can act as an energy pool for emission from the phosphorescent core. The PL quantum yields (PLQYs) are found to be strongly dependent on the dielectric constant of the solvent, ranging from as high as 76% to as low as 0.3%. Neat films of the dendrimers are found to have relatively balanced hole and electron mobilities of order 10–6 cm2 V–1 s–1, with bilayer organic light‐emitting diodes (OLEDs) containing neat emissive layers having a maximum external quantum efficiency (EQE) of 4.7% for a film having a PLQY of 12%. Finally, the solution processed OLEDs fabricated using 0.4 mol% of the dendrimers blended with 9‐[3‐(9H‐carbazol‐9‐yl)phenyl]‐9H‐carbazole‐3‐carbonitrile result in green emission with maximum EQEs of 9.8% and 15.1% for the dendrimers with green and blue emissive TADF dendrons, respectively. [ABSTRACT FROM AUTHOR]

Fluorescent labels have been paramount in the advancement of molecular biology and related fields, for they unveil Nature's unknowns. Numerous labels have been developed that can be attached to most biomolecules via various labeling chemistries. Practitioners are expected to navigate through the growing libraries of fluorescent probes to select the best one for their target application. It is precisely this vast collection of labels that makes the selection process challenging, often leading to non‐ideal choices. Here, we present a meta‐analysis of fluorescent labels data with the intention of facilitating the selection process. We classify tags into molecular (dyes), macromolecular (proteins), and nanoparticles. Groups are then organised into subgroups by chemical structure. Entries were structured based on cost, absorption and emission wavelengths, Stokes shifts, molar extinction coefficients, quantum yields, lifetimes, and brightness. We correlate chemical composition to available photophysical properties of the fluorophores in their bound‐whenever possible‐and unbound states. The limited access to complete, comparable, and meaningful photophysical data for fluorescent labels and to reliable fluorescence standards, where calibration is still challenging and benchmarks are still ill‐defined, are highlighted to raise critical awareness of the current issues hampering further development of the field. [ABSTRACT FROM AUTHOR]

Fluorescence properties of quantum dots (QDs) are critically affected by their redox states, which is important for practical applications. In this study, we investigated the optical properties of MoSe2-metallic phase quantum-dots (MoSe2-mQDs) depending on the pH variation, in which the MoSe2-mQDs were dispersed in water with two sizes (Φ~3 nm and 12 nm). The larger MoSe2-mQDs exhibited a large red-shift and broadening of photoluminescence (PL) peak with a constant UV absorption spectra as varying the pH, while the smaller ones showed a small red-shift and peak broadening, but discrete absorption bands in the acidic solution. The excitation wavelength-dependent photoluminescence shows that the PL properties of smaller MoSe2-mQDs are more sensitive to the pH change compared to those of larger ones. From the time-resolved PL spectroscopy, the excitons dominantly decaying with an energy of ~3 eV in pH 2 clearly show the shift of PL peak to the lower energy (~2.6 eV) as the pH increases to 7 and 11 in the smaller MoSe2-mQDs. On the other hand, in the larger MoSe2-mQDs, the exciton decay is less sensitive to the redox states compared to those of the smaller ones. This result shows that the pH variation is more critical to the change of photophysical properties than the size effect in MoSe2-mQDs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photophysical processes of three 3-carboxy substituted bis-salicylidenes in polar solvents are discussed. • The excited state proton transfer competes with proton donation to the solvent. • Strongly interacting solvents break the internal hydrogen bond and lead to a solvent – assisted excited state proton transfer. • The charged species and the twisted enols outnumber the neutral keto structures in alcohols. • A comprehensive photochemical scheme of the S 1 state deactivation is proposed. The excited state of proton transfer and the dynamics of the excited states of three 3-carboxy substituted bis-salicylidenes (H 4 L1-3) have been studied by combining steady state and time-resolved absorption and emission methods, and with quantum chemical calculations. The 3-carboxy substituted bis-salicylidenes contain two coupled intramolecular hydrogen bonds of the OH...OH...N type. This system has two proton transfer sites. The compounds have excitation – dependent emission and a high sensitivity to the solvent polarity. ESIPT and deprotonation result in the co-existence of enol, keto, anionic and zwitterionic species with or without quinoid structure, whose emission bands are located from the blue to the yellowish-green region. The photophysical processes in the nano-to-microseconds timescale have been linked to the intermolecular interactions with the solvent, where hydrogen bonding leads to the formation of a cyclic 1:2 solute − solvent complex. Transient absorption spectroscopy revealed that the generation of charged structures of H 4 L1-3 occurs through a solvent-assisted proton transfer along the chain of two solvent molecules, which act as a proton-relay system. The computational study of the energy profiles and of the enol-to-keto tautomerization with explicit solvent molecules has been performed for the first time for this kind of ESIPT system. [ABSTRACT FROM AUTHOR]

In this paper, we present for the first time an efficient method for synthesizing three novel tetra–coordinated BF 2 complexes, specifically 6,6-difluoro-2,4-dimethyl-6 H -5λ4,6λ4-benzo [4,5]imidazo(oxazolo/thiazolo)[3,2- c ]pyrimido [2,1- f ][1,3,5,2]triazaborinines (4a–c). These compounds were synthesized via the reaction of selected N -(4,6-dimethylpyrimidin-2-yl)-benzo[ d ]imidazo(oxazolo/thiazolo)-2-amines (3a–c) with BF 3 ·OEt 2 , employing Et 3 N as a base. Optimized yields ranging from 64 to 69 % were achieved when the reactions were conducted in anhydrous CHCl 3 at room temperature for 24 h. The structural elucidation of BF 2 complexes 4a-c was performed through multinuclear NMR, FTIR, SC-XRD, and HRMS techniques. These compounds demonstrated thermal stability up to 150 °C as evidenced by thermogravimetric analysis. The spectroscopic properties (in both solution and solid states) and the electrochemical properties of the synthesized derivatives were thoroughly investigated using UV–Vis spectroscopy, steady-state, time-resolved fluorescence emission, TD-DFT calculations, and redox potential measurements. The results of this study highlighted a dependence of the compounds' properties on the heteroatom (NH, O, or S) present within the heterocyclic skeleton. [Display omitted] • Tetracyclic BF 2 -organoboron complexes as a new luminescent framework is covered. • Complete structural elucidation by NMR, FTIR, TD-DFT and SC-XRD is performed. • Optical in solution, solid-state, AIE phenomenon and redox potential are addressed. • Good thermal stability up to 150 °C and T d = 188–359 °C range given by TGA. [ABSTRACT FROM AUTHOR]

A σ‐bonded platinum(II) diketopyrrolopyrrole (Pt‐DPP) complex was synthesized from a reaction of p‐pinacolatoborylphenyl‐substituted DPP with dichloro(1,5‐cyclooctadiene)platinum(II), followed by a ligand exchange reaction with triphenylphosphine. The Pt‐DPP complex is highly fluorescent not only in solution but also in the solid state. From the comparison of the emission properties with those of N‐benzyl‐DPPs bearing phenyl and p‐bromophenyl substituents, the intense emission of the Pt‐DPP complex is ascribed to the DPP‐centered fluorescence. In the solid state, aggregation‐caused quenching is mitigated by the well‐segregated molecular packing due to the bulky triphenylphosphine ligands. The facile synthesis and unique fluorescence properties of the Pt‐DPP complex are beneficial for creating DPP‐based functional chromophores. [ABSTRACT FROM AUTHOR]

The synthesis of boron difluoride complexes of a series of curcuminoid derivatives containing various donor end groups is described. Time-dependent (TD)-DFT calculations confirm the charge-transfer character of the second lowest-energy transition band and ascribe the lowest energy band to a "cyanine-like" transition. Photophysical studies reveal that tuning the donor strength of the end groups allows covering a broad spectral range, from the visible to the NIR region, of the UV-visible absorption and fluorescence spectra. Two-photon-excited fluorescence and Z-scan techniques prove that an increase in the donor strength or in the rigidity of the backbone results in a considerable increase in the two-photon cross section, reaching 5000 GM, with predominant two-photon absorption from the S0-S2 charge-transfer transition. Direct comparisons with the hemicurcuminoid derivatives show that the two-photon active band for the curcuminoid derivatives has the same intramolecular charge-transfer character and therefore arises from a dipolar structure. Overall, this structure-relationship study allows the optimization of the two-photon brightness (i.e., 400-900 GM) with one dye that emits in the NIR region of the spectrum. In addition, these dyes demonstrate high intracellular uptake efficiency in Cos7 cells with emission in the visible region, which is further improved by using porous silica nanoparticles as dye vehicles for the imaging of two mammalian carcinoma cells type based on NIR fluorescence emission.

Marine Coelenterazine is one of the most well-known chemi-/bioluminescent systems, and in which reaction the chemi-/bioluminophore (Coelenteramide) is generated and chemiexcited to singlet excited states (leading to light emission). Recent studies have shown that the bromination of compounds associated with the marine Coelenterazine system can provide them with new properties, such as anticancer activity and enhanced emission. Given this, our objective is to characterize the photophysical properties of a previously reported brominated Coelenteramide analog, by employing a combined experimental and theoretical approach. To better analyze the potential halogen effect, we have also synthesized and characterized, for the first time, two new fluorinated and chlorinated Coelenteramide analogs. These compounds show similar emission spectra in aqueous solution, but with different fluorescence quantum yields, in a trend that can be correlated with the heavy-atom effect (F > Cl > Br). A blue shift in emission in other solvents is also verified with the F–Cl–Br trend. More relevantly, the fluorescence quantum yield of the brominated analog is particularly sensitive to changes in solvent, which indicates that this compound has potential use as a microenvironment fluorescence probe. Theoretical calculations indicate that the observed excited state transitions result from local excitations involving the pyrazine ring. The obtained information should be useful for the further exploration of halogenated Coelenteramides and their luminescent properties.

Positron emission tomography (PET)–fluorescence imaging is an emerging field of multimodality imaging seeking to attain synergy between the two techniques. The probes employed in PET–fluorescence imaging incorporate both a fluorophore and radioisotope which enable complementary information to be obtained from both imaging techniques via the administration of a single agent. Fluorine‐18 is the most commonly used radioisotope in PET imaging and consequently many novel attempts to radiofluorinate various fluorophores have transpired over the past decade. In this Minireview, the most relevant fluorine‐18 labelled PET–fluorescence probes have been classified into four groups as per the implemented fluorophore: 1) boron‐dipyrromethene (BODIPY) dyes, 2) cyanine dyes, 3) alternative organic fluorophores and 4) organometallics, such as quantum dots (QDs) and rhenium complexes. The biological, radiochemical and photophysical properties of each probe have been systematically compared to aid future endeavours in PET–fluorescence chemistry. [ABSTRACT FROM AUTHOR]

Apart from numerous applications, for example in azo dye precursors, explosives, and industrial processes, the nitro group (−NO2) appears on countless molecules in photochemical research owing to its unique characteristics such as a strong electron‐withdrawing ability and facile conversion to the reduced substituent. Although it is well known as a fluorescence quencher, fluorescent chromophores that contain the nitro group have also emerged, with 3‐nitrophenothiazine being recently reported to have 100 % emission quantum yield in nonpolar solvents. The diverse characters of nitro‐containing chromophores motivated us to systematically review those chromophores with nitro substituents, their associated photophysical properties, and applications. In this Review, we succinctly elaborate the advance of the fluorescent nitro chromophores in fields of intramolecular charge transfer, fluorescent probes and nonlinear properties. Special attention is paid to the rationalization of the associated emission spectroscopy, so that the readers can gain insights into the structure‐photophysics relationship and hence gain insights for the strategic design of nitro chromophores. [ABSTRACT FROM AUTHOR]

We present a femtosecond pump-probe UV-Vis broadband transient absorption spectroscopy study of two styryl-substituted BODIPY chromophores with different position of the substituent. The α-substituted isomer shows typical BODIPY-type spectral features, such as sharp absorption and emission bands, a small Stokes shift and an excited-state lifetime in the 4 ns range, which only weakly depends on the solvent. In contrast, β-styryl-BODIPY features much broader steady-state absorption and emission spectra and a larger Stokes shift, particularly in polar solvents. Transient absorption spectroscopy including a complete global kinetic analysis reports a substantial decrease in S1 lifetime to 300 ps for polar solvents upon change from α- to β-substitution. In the case of the α-isomer, TD-DFT calculations identify a typical "cyanine-type" electron rearrangement upon S0 → S1 excitation accompanied by a slight reduction in dipole moment. In contrast, the same transition in the β-isomer shows strong intramolecular charge transfer (ICT) character involving a substantial increase in dipole moment. Assuming a simple energy-gap-law argument, the accelerated nonradiative decay of the β-isomer in polar solvents may be linked to the decrease of the S1(ICT)-S0 energy difference. BODIPY dyes with a conjugated substituent in β-position therefore suffer a substantial loss in fluorescence brightness in polar environments compared with their α-substituted counterparts. This might limit their applicability in fluorescence imaging. [ABSTRACT FROM AUTHOR]

Labeling cells and tissues with fluorescent probes, such as organic dyes and quantum dots (Qdots) is a widespread and successful technique for studying molecular dynamics both in vitro and in vivo. However, those probes usually suffer from undesirable photophysical/photochemical processes, such as blinking and photobleaching, limiting their utilization. The main challenges in fluorescent probe design are to improve their absorption/emission properties, and to provide higher stability against photobleaching. In the last few years, metallic nanoparticles (NPs) of various sizes, shapes, and compositions have been used as a new alternative for cellular microscopy. This is in part because-unlike common organic dyes and Qdots-metallic NPs do not bleach or blink upon continuous illumination, are extremely stable, very bright, and their luminescence spans over the visible spectrum. These characteristics make them attractive contrast agents for cell imaging both in vitro and in vivo. For these reasons, the emission of metallic NPs in bulk solutions has already been extensively characterized. In contrast with bulk experiments, where billions of molecules are measured simultaneously, single-particle techniques allow the observation of characteristics and dynamical processes otherwise hidden in the measured average. A full understanding of the photophysical properties of the NPs is critical when they are used for single-molecule applications. Photophysical processes can be a source of artifacts if they are not interpreted accordingly, and thus a careful characterization of these labels at the single-particle level became crucial for the correct interpretation of the experimental results. Herein, we study some of their unique optical properties at the single-particle level and show examples that illustrate their intrinsic heterogeneity when used in biological environments.

Conformational changes of linker units in metal‐organic frameworks (MOFs) are often responsible for gate‐opening phenomena in selective gas adsorption and stimuli‐responsive optical and electrical sensing behaviour. Herein, we show that pressure‐induced bathochromic shifts in both fluorescence emission and UV/Vis absorption spectra of a two‐fold interpenetrated Hf MOF, linked by 1,4‐phenylene‐bis(4‐ethynylbenzoate) ligands (Hf‐peb), are induced by rotation of the central phenyl ring of the linker, from a coplanar arrangement to a twisted, previously unseen conformer. Single‐crystal X‐ray diffraction, alongside in situ fluorescence and UV/Vis absorption spectroscopies, measured up to 2.1 GPa in a diamond anvil cell on single crystals, are in excellent agreement, correlating linker rotation with modulation of emission. Topologically isolating the 1,4‐phenylene‐bis(4‐ethynylbenzoate) units within a MOF facilitates concurrent structural and spectroscopic studies in the absence of intermolecular perturbation, allowing characterisation of the luminescence properties of a high‐energy, twisted conformation of the previously well‐studied chromophore. We expect the unique environment provided by network solids, and the capability of combining crystallographic and spectroscopic analysis, will greatly enhance understanding of luminescent molecules and lead to the development of novel sensors and adsorbents. [ABSTRACT FROM AUTHOR]

Solvent‐dependent switching of graphene oxide (GO) as fluorescence quencher or enhancer was observed. In some solvents, GO increases the fluorescence yield of a hydrophilic molecule 7‐(diethylamino)‐coumarin‐3‐carboxylic acid (7‐DCA), and in some solvents GO act as a quencher of fluorescence. [ABSTRACT FROM AUTHOR]

A series of indole-based helicenes, namely, 15-hexyl-15Htetraphenyl[1,2-e]indole (HTPI), 14-hexyl-14H-benzo[4’,5’]thieno [2’,3’:7,8]naphtha[1,2-e]indole (HBTNI), 7-hexyl-7H-indolo[5,4-k] phenanthridine (HIPD) and 3-hexyl-3H-phenanthro[4,3-e]indole (HPI) were successfully synthesized by three- or four-step reactions. They exhibited good solubility and high thermal stability of Td=247, 388, 294 and 251°C, respectively. These compounds emit violet-blue light with maximum emission peaks at 415, 397, 397 and 391 nm in hexane. Among them, HBTNI had excellent thermal stability, narrow and sharp emission peaks, and highest photoluminescence quantum yield (0.32). Thus, HBTNI was an ideal candidate for the violet-blue emitters of OLEDs. Furthermore, the four compounds had twophoton absorption and two-photon excited fluorescence. HTPI showed the maximum TPA with the TPA cross-section (δ) of 171.5 GM at 770 nm. They were rare examples of helicenes with both violet-blue emission and TPA. [ABSTRACT FROM AUTHOR]

The tendency of boron-dipyrromethene (BODIPY) dyes to associate in water is well known, and usually a cause for inferior fluorescence properties. Synthetic efforts to chemically improve BODIPYs' water solubility and minimize this problem have been numerous in the past. However, a deeper understanding of the phenomena responsible for fluorescence quenching is still required. Commonly, the spectroscopic behaviour in aqueous media has been attributed to aggregate or excimer formation, with such works often centring on a single BODIPY family. Herein, we provide an integrating discussion including very diverse types of BODIPY dyes. Our studies revealed that even subtle structural changes can distinctly affect the association behaviour of the fluorophores in water, involving different photophysical processes. The palette of behaviour found ranges from unperturbed emission, to the formation of H or J aggregates and excimers, to the involvement of tightly bound, preformed excimers. These results are a first step to a more generalized understanding of spectroscopic properties vs. structure, facilitating future molecular design of BODIPYs, especially as probes for biological applications. [ABSTRACT FROM AUTHOR]

The syntheses and crystal structures of sterically crowded mono‐ and bichromophoric BODIPY‐based dyes are reported. The "monomeric" compound is weakly fluorescent in the liquid phase due to fast internal conversion associated with rotation of aryl rings at the boron atom. The side‐by‐side "dimer" exhibits weak excitonic coupling between the dipyrrin units and is much more emissive in fluid solution. Solid samples of both molecular entities are strongly fluorescent under near‐UV illumination. Thus, the mono‐chromophore exhibits dual fluorescence from what appears to be a mixture of crystalline and possibly amorphous (or interfacial regions) distributions. The bi‐chromophore packs in the crystal as pairs of chromophores with each unit being provided by a different molecule. This leads to excitonic splitting and the formation of a strong H‐band in the absorption spectrum. Fluorescence occurs from the corresponding J‐species and also from what appears to be an aggregated state associated with interfacial areas. Both bulk and interface‐bound states show relatively long‐lived fluorescence while the crystal structures indicate the likelihood for fast electronic energy migration between molecules. [ABSTRACT FROM AUTHOR]

The fluorescent dye perylene‐3,4,9,10‐tetracarboxylic dianhydride (PBA) was immobilized onto polysulfone hollow fibers by means of a wet coating procedure. After immobilization, PBA was able to react with primary amines through a double anhydride ring opening reaction. The in situ amine coupling was further revealed by fluorescence analysis. Both emission (534 nm →538 nm) and fluorescence lifetime changes (2.7 ns →3.3 ns) of the dye are a useful tool to detect and visualize the occurrence of the reaction. The successful implementation of amine coupling with a reporting function on polysulfone fibers holds great interest for biomedical applications. [ABSTRACT FROM AUTHOR]

Two A‐π‐D‐π‐A thiophene‐based small molecules with a central dithienosilole core and dicyanovinyl (DCV) end groups were synthesized. These compounds differ only by the presence of alkyl and alkylsulfanyl chains, respectively, on the thiophene beta positions. Computational data together with the spectroscopic and electrochemical findings (obtained by means of absorption, steady‐state/time‐resolved emission techniques, and cyclic voltammetry) revealed that both molecules possess low electronic and optical band gaps, broad absorption spectra, and good stability both in p and n‐doping states, which make them suitable for optoelectronic applications. In both compounds, the HOMO–LUMO transition involves an intramolecular charge transfer from the electron‐donor dithienosilole unit to the two terminal electron‐acceptor DCV groups. A marked positive emission solvatochromism was observed for both molecules and was interpreted on the basis of the symmetry breaking in the S1 excited state. The two synthesized compounds were also compared to their shorter precursors and to similar oligothiophenes to understand how the nature of the building block influences the characteristics of the final materials. Furthermore, it was possible to better understand the contribution of the sulfur atom in modulating the optical properties of the small molecules studied. [ABSTRACT FROM AUTHOR]

In this work, we have performed an in-depth study of the photophysics and solvatofluorochromism of a red-emitting Si-xanthene dye, an analog of Tokyo Magenta (TM) historically developed by Egawa et al. (Chem. Commun. 2011 , 47 , 4162–4164). The results show a strong dependency of the emission properties of 2-Me-4-OMe-TM on the polarity of the solvent. For instance, the dye exhibited an increase in its fluorescence lifetime with the decrease in solvent polarity. Therefore, in this work, this spectral behavior has been used as a new approach for determining the intracellular microenvironment polarity through the measurement of its fluorescence lifetime by Fluorescence Lifetime Imaging Microscopy (FLIM). Our experiments confirmed the ability of the dye to detect changes in polarity between different intracellular compartments. Image 1 • A silicon-substituted xanthene dye was synthesized and its photophysics studied. • The dye shows a strong solvatochromic behavior involving two emission bands. • A strong dependency on the solvent's acidity was observed in the red-shifted band. • The dye works as an intracellular polarity fluorescence lifetime sensor. [ABSTRACT FROM AUTHOR]

We describe here the preparation of a series of trans‐ABAB Zn(II) phthalocyanines (ZnPcs, which combine several interesting features. First, these compounds present high solubility and hindered aggregation, due to the functionalization of two facing isoindole constituents (B) of the ZnPc with bis(trifluoromethylphenyl) units. Second, the other two isoindoles (A) bear extra‐annulated phthalimide units containing different substituents in the nitrogen positions, this feature results in a collinear arrangement of a variety of functional groups. Some of these collinearly functionalized ZnPcs are interesting building blocks for constructing either homo‐ or heteroarrays containing ZnPc units. Furthermore, the amphiphilic nature of some members of the series renders them interesting candidates for photosensitization of singlet oxygen. Photophysical studies on a model compound of the series have shown that these molecules are efficient singlet oxygen photosensitizers in both polar and apolar media, with 1O2 quantum yields (φΔ) as high as 0.74. [ABSTRACT FROM AUTHOR]

• A synthesized BODIPY-benzimidazole conjugate (BDZ) displays high binding affinity towards BSA with a binding constant of (1.38 ± 0.09) × 104 M−1. • Binding of BDZ with BSA casues significant modulations in the photophysical properties of BDZ due to structural immobilization of the dye inside the binding pocket of BSA. • Ionic strength dependent measurements suggest the prominence of hydrophobic interactions between BDZ and BSA. • Molecular docking calculations suggests site IB of BSA to be the most probable binding site for BDZ. Non-covalent interactions of different dyes/drugs with various biological agents, which lead to large modulations in photophysical properties, have attracted attention of many scientists over the decades due to their versatile applicability in different fields. Herein, we report the spectroscopic investigation of non-covalent interaction of a synthesized BODIPY-benzimidazole conjugate (BDZ) dye with bovine serum albumin (BSA), which results in distinctive modulations in the photophysical properties of the dye. The structural immobilization, and reduced propensity of forming the weakly emissive intramolecular charge transfer (ICT) state of the dye, inside the confined BSA cavity, results into a significant increase in fluorescence intensity, which is also supported by the increase in the excited-state lifetime and fluorescence anisotropy decay time of the dye. Molecular docking calculations and competitive binding experiments reveal that the BDZ dye binds selectively to site IB with a reasonably high binding constant K b ˜ 1.38 × 104 M−1. The BDZ-BSA complex shows a notable decrease in fluorescence intensity in the presence of guanidinium hydrochloride, indicating the selective binding of the dye with the native form of the BSA protein as compared to its denatured form. Formation of BDZ-BSA complex, which emits in the biologically favorable red region, makes the studied system a probable choice to monitor the denatured form of the BSA protein, biological sensing study, and to understand the transport mechanism of similar kind of drugs and other metabolites with serum albumin protein. [ABSTRACT FROM AUTHOR]

Abstract In this work, the rotational dynamics and photophysics of three structurally similar, coumarins: Coumarin 6, Coumarin 7 and Coumarin 30 in the deep eutectic solvent (DES) have been studied by using steady-state and time-resolved fluorescence emission spectroscopy, with the variation of temperature. In our system, with the increase in temperature, the fluorescence lifetime and average rotational relaxation time decreases in a regular manner for three coumarin dyes. From the temperature dependent study, we have estimated the activation energy of non-radiative decays in DES. It has been observed that below 298 K the anisotropy decay can't be fitted due to the hindered motion. However, the above 298 K anisotropy decays are fitted by stretched exponential functions. The rotational dynamics have been analyzed by Stokes-Einstein-Debye (SED) hydrodynamic model of rotational diffusion theory. We have observed significant deviation of rotational dynamics deviation from hydrodynamic theory. We have also reported absolute fluorescence quantum yield of three coumarin dyes in DES for the first time in the literature. Additionally, we have carried out fluorescence lifetime imaging study to understand the distribution of fluorescence lifetime of coumarin molecules in DES. Highlights • Rotational relaxation dynamics of three coumarin molecules were reported in deep-eutectic solvent. • Absolute fluorescence quantum yield of three coumarin molecules in deep-eutectic solvent was reported. • Structural heterogeneity of the medium play crucial role to guide the photophysics of coumarins in DES. • Fluorescence lifetime imaging study shows the distribution of fluorescence lifetime of coumarin molecules in DES. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Zn and In tetramorpholine phthalocyanines are synthesized and then quaternized. • Photodynamic antimicrobial chemotherapy activities towards inactivation of E. coli, S. aureus, and C. albican were evaluated. • The quaternized derivatives showed total elimination of the micro-organism with log reductions greater than 9. Abstract In this study, novel metal-free, zinc and indium 1(4),8(11),15(18),22(25)-tetramorpholine (1a , 2a , 3a respectively) and 2(3), 9(10), 16(17),23(24)-tetramorpholine (1b , 2b , 3b respectively) phthalocyanines were synthesized and complexes 2 and 3 were quaternized. The photophysical and photochemical properties were investigated in dimethylsulfoxide. The non-peripherally substituted phthalocyanines generated higher singlet oxygen than the peripherally substituted phthalocyanines. Photodynamic antimicrobial chemotherapy activities towards inactivation of Escherichia coli, Staphylococcus aureus and Candida albican were evaluated, where all the quaternized Pcs showed total elimination of the micro-organism with log reductions greater than 9. Though the neutral Pcs had log reductions less than 2, for C. albican the percentage reduction was 68.5% for 2b showing the antifungal properties of the morpholine group. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Photophysical properties of a ratiometric amyloid probe have been investigated. • Role of solvent polarity and solute‐solvent H‐bonding on the amyloid sensing behavior of the sensor has been understood. • H-bonding with solvent leads to molecular twisting resulting large decrease in emission yield in polar protic solvents. Abstract Detailed photophysical properties of 2-[2′-Me,4′-(dimethylamino)-phenyl]benzothiazole (2Me-DABT), a potential ratiometric amyloid fibril sensor, have been investigated in different solvents and solvent mixtures using steady state and time-resolved spectroscopic techniques. Our studies show that emission properties of 2Me-DABT are significantly modulated by polarity of solvent media. Extent of solvatochromism (3585 cm−1) shown by 2Me-DABT is quite large and can be used to monitor micropolarity of different complex media. Further, Stokes' shift (>10,000 cm−1) shown by 2Me-DABT in all studied solvents is also much larger than most common molecular probes. It has also been shown that hydrogen bonding with solvent molecules results in large modulation in photophysical properties of 2Me-DABT. The H-bonding with water molecules induces a large change (39°) in the dihedral angle between benzothiazole and aniline moieties resulting large changes in photophysical properties of 2Me-DABT in polar protic solvents. Photophysical properties reported herein are used to explain observed amyloid sensing behaviour of 2Me-DABT. Detailed quantum chemical calculations are performed to support the experimental results. [ABSTRACT FROM AUTHOR]

The synthesis and the photophysical properties of a new class of fully organic monodisperse nanoparticles for combined two‐photon imaging and photodynamic therapy are described. The design of such nanoparticles is based on the covalent immobilization of a dedicated quadrupolar dye that combines excellent two‐photon absorbing (2PA) properties, fluorescence and singlet oxygen generation ability, in a phosphorous‐based dendrimeric architecture. First, a bifunctional quadrupolar dye bearing two different grafting moieties, a phenol function and an aldehyde function, was synthesized. It was then covalently grafted through its phenol function to a phosphorus‐based dendrimer scaffold of generation 1. The remaining aldehyde functions were then used to continue the dendrimer synthesis up to generation 2, introducing finally 24 water‐solubilizing triethyleneglycol chains at its periphery. A dendrimer confining 12 photoactive quadrupolar units in its inner scaffold and showing water solubility was thus obtained. Interestingly, the G1 and G2 dendrimers retain some fluorescence as well as significant singlet oxygen production efficiencies while they were found to show very high 2PA cross‐sections in a broad range of the NIR biological spectral window. Hydrophilic dendrimer G2 was tested in vitro on breast cancer cells, first in one‐ and two‐photon microscopy, which allowed for visualization of their cell internalization, then in two‐photon photodynamic therapy. While being nontoxic in the dark and, more importantly, under exposure to daylight, dendrimer G2 proved to be a very efficient cell‐death inducer only under two‐photon irradiation in the NIR. (Cell) death by day or night: New dendrimers combining high two‐photon brightness and photosensitizing properties are efficient cell‐death inducers under two‐photon irradiation in the NIR, while being non‐toxic in the dark and under exposure to daylight. [ABSTRACT FROM AUTHOR]

Abstract The BOPHY structural scaffold provides opportunities for the synthesis of innumerable derivatives with linear geometries and well-controlled π-conjugation pathways. The simpler BOPHY chromophores are highly fluorescent but exhibit poor mirror symmetry between absorption and fluorescence spectra at ambient temperature. In particular, the absorption (and excitation) spectra are broad and appear as two overlapping bands of comparable intensity. In constrained media, such as low-temperature rigid glasses or stretched poly(ethylene) films, mirror symmetry is restored. Analysis of the temperature dependence recorded for simple BOPHY derivatives indicates that the vibronic envelope accompanying the electronic transitions can be well described in terms of low- and medium-frequency modes. Whereas the fluorescence spectral profile is only weakly dependent on temperature, the excitation spectrum is far more affected. The magnitude of the low-frequency mode, and the associated electron-phonon coupling, increase substantially with increasing temperature and is responsible for temperature broadening and distortion of the excitation spectrum in solution. This critical low-frequency vibronic mode is associated with out-of-plane torsional bending of the BOPHY unit. Variable temperature NMR studies failed to provide unequivocal evidence for conformational changes of one of the derivatives over the temperature range 193–353 K. Graphical Abstract Unlabelled Image Highlights • Excitation and fluorescence spectra have been recorded over a wide temperature range. • Optical spectra have been recorded with the compound in a stretched polythene film. • Spectra have been subjected to a detailed curve-fitting analysis. • A key feature of this analysis relates to the involvement of a low-frequency vibration. • Mirror symmetry is restored in solid media where local structural perturbations are hindered. [ABSTRACT FROM AUTHOR]

The fluorescence intensity of a C‐terminal acceptor chromophore, N‐(7‐dimethylamino‐4‐methyl coumarin (DACM), increased proportionally with 280 nm irradiation of an increasing number of donor tryptophan residues located on a β‐sheet forming polypeptide. The fluorescence intensity of the acceptor chromophore increased even as the length of the β‐sheet edge approached 256 Å, well beyond the Förster radius for the tryptophan–acceptor chromophore pair. The folding of the peptides under investigation was verified by circular dichroism (CD) and deep UV resonance Raman experiments. Control experiments showed that the enhancement of DACM fluorescence occurred concomitantly with peptide folding. In other control experiments, the DACM fluorescence intensity of the solutions of tryptophan and DACM did not show any enhancement of DACM fluorescence with increasing tryptophan concentrations. Formation of fibrillar aggregates of the substrate peptides prepared for the fluorescence studies was undetectable by thioflavin T (ThT) fluorescence. Genetically engineered polypeptides (GH6[(GA)3GK(GA)3GW(GA)3GE(GA)3 GW]4GAC1‐DACM), (GH6[(GA)3 GK(GA)3GW(GA)3GE(GA)3GW]8GAC1‐DACM), (GH6[(GA)3GK(GA)3GW(GA)3GE (GA)3GW]12GAC1‐DACM) and (GH6[(GA)3GK(GA)3GW(GA)3 GE(GA)3 GW]16GAC1‐DACM) folded to form β‐sheet assemblies. On irradiation at 280 nm, the transfer of excited‐state energy to the terminally placed dimethylaminocoumarin (DACM) acceptor chromophores increased proportionally with increasing numbers of donor tryptophans, even as β‐sheet edge distances exceeded 200 Å. [ABSTRACT FROM AUTHOR]

Blue thermally activated delayed fluorescent (TADF) devices with short excited‐state lifetime, high reverse intersystem crossing rate, and low‐efficiency roll‐off were developed by managing the molecular structure of donor–acceptor‐type blue emitters. Three isomers of blue TADF emitters with a diphenyltriazine acceptor and three carbazole donors were synthesized. The position of the donor moieties in the phenyl linker connecting the donor and acceptor moieties was controlled to devise compounds with a short delayed fluorescence lifetime. A blue TADF emitter with three carbazole donors at 2‐, 3‐, and 4‐ positions of a phenyl linker shortened the excited state lifetime to 4.1 μs, showed a high external quantum efficiency of 20.4 %, and low efficiency roll‐off of less than 10 % at 1000 cd m−2. Therefore, a molecular design distorting the donors by aligning them in a consecutive way is useful to resolve the issues of long delayed fluorescence lifetime and efficiency roll‐off of blue TADF devices. Blue fluorescent emitters: Blue thermally activated delayed fluorescent emitters 234CzTrz, 235CzTrz, and 245CzTrz were synthesized with variation of positions of the donor substituents on the phenyl linker connecting the donor and acceptor moieties. 234CzTrz showed higher photoluminescence quantum yield and shorter excited‐state lifetime than its isomers because of the highly twisted donor and acceptor units (see figure). [ABSTRACT FROM AUTHOR]

i‐Motifs are tetraplex DNAs known to be stable at acidic pH. The structure of i‐motifs is important in DNA nanotechnology; i‐motif‐forming sequences with consecutive cytosine (C) molecules are abundant throughout the human genome. There is, however, little information on the structure of C‐rich DNAs under physiologically relevant neutral conditions. The electron dynamics of i‐motifs, crucial to both biology and materials applications, also remains largely unexplored. In this work, we report a combined femtosecond and nanosecond broadband time‐resolved fluorescence (TRF) and steady‐state fluorescence investigation on homo‐oligomer dC20, a human telomeric sequence (HTS) 5′‐dC3(TA2C3)3, and its analogue performed with different excitation at both acidic and neutral pH. Our study provides direct observation of intrinsic fluorescence and the first full probe of the real‐time dynamics of the intrinsic fluorescence from i‐motifs formed from varied sequences and pH conditions. The results obtained demonstrate concrete evidence for the existence at neutral pH of i‐motifs from both dC20 and the HTS. It also identifies that, under neutral conditions, the i‐motif from dC20 adopting the bimolecular folding structure is significantly more stable than the HTS i‐motif featuring the unimolecular topology. Our femtosecond and nanosecond TRF study unveils excitation dynamics distinctive of the interdigitated architecture of i‐motifs with the excited states involved exhibiting deactivation over a remarkably broad timescale through multiple channels involving proton‐coupled electron transfer lasting tens of picoseconds, as signified by the solvent kinetic isotope effect, and structure‐dependent charge recombination in the hundreds of picoseconds to tens of nanoseconds time regime. Return to the fold: Intrinsic fluorescence measurements revealed formation of i‐motifs at neutral pH from both the homo‐cytosine oligomer and C‐rich human telomeric DNA that possess largely varied structural stability owing to the difference in folding molecularity (see figure). Studying the intrinsic fluorescence from these i‐motifs uncovered multiple timescale electron dynamics distinctive of the interdigitated architecture of i‐motifs. [ABSTRACT FROM AUTHOR]

Energy transfer cassettes that build on the platform of boronic acid derived salicylidenehydrazone (BASHY) complexes were prepared. The functional flexibility of the BASHY chromophore was underpinned by its tunable role as energy donor or acceptor, integrated in compact and non‐conjugated bichromophoric dyads. The energy transfer is highly efficient (ΦET>0.95) and is assumed to proceed mainly via a through‐bond mechanism. Both constituent chromophores benefit mutually from their integration in the cassettes: a) The pseudo Stokes shift is increased to 110–200 nm; b) the antenna (donor) chromophore improves the light absorption of the acceptor chromophore; and c) the emission window of the BASHY chromophore is expanded in the BASHY‐Bodipy dye without using strategies that compromise the observation of high quantum yields. The application of the cassettes for the formulation of fluorescent polymeric nanoparticles, that can be internalized in cells and observed by fluorescence imaging, was demonstrated using the BASHY‐Bodipy dye as an example. Stronger together: The boronic acid derived salicylidenehydrazone (BASHY) dye platform has been integrated in energy transfer cassettes, showing high photophysical flexibility. Brightly fluorescent dyes where obtained that can be formulated with polymeric organic nanoparticles with application potential in bioimaging. [ABSTRACT FROM AUTHOR]

Two novel phthalonitrile derivatives, bearing two hexyloxy groups and a benzodioxin (or a naphthodioxin) annulated ring, along with their corresponding metal-free phthalocyanines (H2Pc) were prepared. FT-IR, mass, electronic absorption, 1H NMR, and 13C NMR spectroscopy were employed for the characterization of all compounds. The effect of hexadeca substituents on the photophysical properties of metal-free Pcs was investigated. Photophysical properties of H2Pc were studied in tetrahydrofuran (THF). Fluorescent quantum yields of phthalocyanines (Pcs) were calculated and compared with the unsubstituted phthalocyanine. 1,4-Benzoquinone effectively quenched the fluorescence of these compounds in THF. Cyclic and square wave voltammetry methods were applied to metal-free phthalocyanines and Pc-centered oxidation and reduction processes were obtained.