Molecular organic photocatalysts developed for use in chemical transformation reactions have gained momentum in recent years. In this study, six new triplet photosensitizers were prepared to determine their photocatalyst capabilities and chemical transformation abilities. The chemical structures of the synthesized orthogonal BODIPYs and their cyclotriphosphazene derivatives were analyzed and then their photophysical characteristics including the UV-Vis absorption spectra, fluorescence emission spectra, fluorescence quantum yields, were investigated. The quantitative singlet oxygen formation was determined by chemical trapping using DPBF (diphenylisobenzofuran). In particular, cyclotriphosphazene derivative 12 having three BODIPY moieties showed efficient singlet oxygen production with high photostability and good molar extinction coefficient. The photo-oxidation ratio constant of 1,5-dihydroxynaphthalene (DHN) was calculated as 28.7 × 10-3 min-1 for compound 12 and at the end of 22.5 min., DHN converted to juglone with 100% efficiency. In addition, the ability of the compounds to convert 1,3-cyclohexadiene into peroxides in the presence of molecular oxygen and light was investigated and the conversion efficiency was determined by NMR technique. All compounds have been presented as photocatalysts for use in different synthetic photochemistry applications.

Abstract. The pH-dependent UV/Vis absorption and fluorescence of several analogs of the marine natural product ageladine A were investigated. Besides ageladine A itself, its BF2 complex, and the corresponding debrominated analogs were included, as were the chloro analog of the debromoageladine-BF2 complex, an imidazolone analog, and a triazole derivative, which lack the free amino group. Importantly, the pH-dependence of the fluorescence of the chloro analog closely resembles that of the natural product ageladine A, but with about 25-fold higher fluorescence intensity and a maximum between pH 3 and 6. The imidazolone derivative behaves in a complementary manner and shows fluorescence only above pH 6, but with less intensity than ageladine A. The calculated Stokes shifts agrees well with the experiment, which underlines the accuracy of the DFT calculation method (ωB97XD/TApr-cc-pVDZ, water, PCM). The combination of BF2 units with arylated imidazo[4,5-c]pyridine structural motifs encourages further research on more strongly fluorescent derivatives of comparable molecular size.

In this study, we investigate the effect of terminal benzene derivatives in triphenylamine-based oxime esters on their photoreactivity. Five novel oxime esters ( Miko series) that containing different benzene derivatives as terminal groups, were synthesized. The electronic properties of the substituents on the benzene ring range from electron-donating to electron-withdrawing. Specifically, a methoxy benzene for Miko-MOB, tert-butyl benezene for Miko-t-Bu, chloro benzene for Miko-CB, trifluoromethyl benzene for Miko-TFM, and nitro benzene for Miko-NB. Additionally, a compound with benzene only as the terminal substituent (TP-1) was selected for comparision. All the new compounds exhibited higher molar extinction coefficients than TP-1. Additionally, the steady-state photolysis and electron spin resonance (ESR) properties would decrease from the electron-donating substitutes to electron-withdrawing substitutes. Finally, these oxime esters are utilized in Type I photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) under UV or LED@405 nm light irradiation conditions. Among all formulations, Miko-MOB demonstrated the highest double bond conversion efficiency under both UV and LED@405 nm light irradiation. Thus, terminal benzene derivatives in oxime esters play an important role in tuning the optical and photochemical reaction performance, offering significant value for the design strategy of such photoinitiators.

Heterogeneity in the fluorescence of carbon dots (CDs) has been hard to figure out so far. This could potentially be related to structural factors, size or intermediate fluorophores, especially when employing the bottom-up synthesis. Herein, we unveil the origin of fluorescence and spectral heterogeneity of CDs using a simple dynamic method. This work reports the room light-excited green fluorescence and dual-emissive N-doped CDs synthesized using a hydrothermal method. Studies were carried out considering the factors of fluorescence phenomena, such as excitation-independent emission, fluorescent impurities, aggregation and solvation dynamics. The new steady-state, Excitation-resolved area-normalized emission spectroscopy (ERANES) and ensemble measurements, including time-resolved studies reveal that a heterogeneous environment exists in the ground state. Eventually, the results show the existence of core, edge and surface states in the CDs. Additionally, the fluorescence characteristics depend on the structural functionalization that occurs in both the intrinsic and extrinsic states of the CDs and it is proven that this does not violate the Kasha-Vavilov rule. Although a highly purified material could still exhibit heterogeneity due to the ensemble emissive states and structural variations. Our results provide insights into the enduring debates about fluorescence and a deeper understanding of the structure- property relationship of CDs.

The structural uniqueness of covalent organic frameworks (COFs) has brought great potential for their applications in photocatalysis. However, existing linkages of COF always lead to poor electron delocalization and inadequate stability. Therefore, two novel azo-linked COFs AZO-B-COF and AZO-T-COF were successfully constructed by the monomer exchange method. Significantly, two as-synthesized azo COFs presented a much higher photodegradation rate of 96% and 51% for AZO-T-COF and AZO-B-COF, respectively, which was in sharp contrast to the almost 0 degradation rate of imine COFs. And as expected, AZO-T-COF could be cycled at least 5 runs without a significant decrease in catalytic efficiency. Systematical experiments and theoretical calculations showed that comparing with imine COFs, conjugated structure of azo COFs broadened the visible-light absorption range and improved the transfer efficiency of the photocarriers. The N-rich azo bonds acted as an electron acceptor and made the materials better planarity. This work not only enriches COFs family but also demonstrated the superiority of azo-linked COFs.

The great demand for visible-light-induced catalysts with high photocatalytic performance has stimulated extensive interest in constructing g-C3N4-based Z-scheme heterojunctions. In this research work, we constructed the g-C3N4/Bi2O3 Z-scheme heterojunction by precipitation-hydrothermal method, and confirmed the close contact interface between g-C3N4 and Bi2O3 to form the heterojunction by various characterization techniques, which facilitates the efficient separation of photogenerated electrons-holes. Compared to pure g-C3N4 and Bi2O3, the g-C3N4/Bi2O3-1 composite exhibited a transient photocurrent response approximately 7 and 5 times higher than that of g-C3N4 and Bi2O3, respectively, with stronger visible photocatalytic activity and degraded 99.8% methylene blue within 75 min. Ion trapping experiments showed that •OH free radical had the greatest effect on the degradation of methylene blue, while •O2- and h+ had less effect. According to the experimental test results, the possible photocatalytic degradation mechanism of g-C3N4/Bi2O3-1 catalyst was proposed. This study provides a new avenue for the development of novel g-C3N4-based Z heterojunction materials with application value.

Understanding the structure-function relationships of the green fluorescent protein (GFP) chromophore is important in rationally developing new molecular tools for biological imaging and beyond. Herein, we systematically modified the GFP chromophore structure with electron-withdrawing and -donating groups (EWGs and EDGs) to investigate the substituent effects on the excited-state proton transfer (ESPT) and twisting dynamics of the cationic chromophore in solution. With key insights gained from femtosecond transient absorption and stimulated Raman spectroscopy, we reveal that the EWG substitution by –F increases photoacidity in an additive manner and leads to an ultrafast barrierless ESPT by difluorination, while the EDG substitution by –OCH3 also results in ultrafast ESPT despite the weak photoacidity as estimated by the Förster equation. We ascribe the unusually fast kinetics in methoxylated derivatives to the occurrence of a pre-existing chromophore-solvent complex that sets up the acceptor site for ESPT. Furthermore, the kinetic competition between ESPT and twisting pathways is crucial for the observation of ESPT in action, particularly for molecules undergoing efficient nonradiative decay in the excited state through torsional motions. Such flexible and highly engineerable molecules can enable more versatile photoswitches and sensors.

The triplet-sensitized (by the solvent acetone) as well as the direct (λex = 300 - 320 nm) photochemical decarboxylation of N-phthaloylated γ-aminobutyric acid (GABA) derivatives are versatile and high-yielding routes to benzopyrrolizidines via intramolecular electron transfer initiated decarboxylation followed by radical coupling. The ß-mono- and ß,ß´-disubstituted N-phthaloyl GABA derivatives 7a-7g, respectively, were applied as substrates. Decarboxylative photocyclization yielded hydroxy benzopyrrolizidines 8a-8g in high chemical yields and with moderate diastereoselectivities from the ß-monosubstituted substrates. The analogous α-substituted GABA derivatives 11a-11c were also applied as potential substrates for memory of chirality effects. The reaction quantum yields of the photodecarboxylation reactions for the parent GABA derivative 13 and for the new substrates 7h and 11a were determined by the quantum yield determination system (QYDS) and showed a remarkable concentration dependency indicating aggregation at higher substrate concentrations. Inhibition studies on the atherogenic human serine hydrolase cholesterol esterase showed derivatives 8a and 8d to exhibit a hyperbolic mode of inhibition with moderate IC50 values of about 60-80 µM.

Quantum chemistry methods have been enacted to characterize the second-order nonlinear optical (NLO) properties of a multi-state molecular switch combining dihydroazulene and spiropyran units. They have demonstrated that the first hyperpolarizabilities constitute a novel output signal from the viewpoint of molecular logic, owing to the contrasts of NLO responses between the different forms of the dyad. On the one hand, the DFT calculations demonstrate that switching either unit has only a negligible impact on the geometrical parameters of the other one, as well as on the thermodynamics of their transformations. Similarly, as determined by time-dependent DFT calculations, the UV/vis absorption spectra are in good approximation a superposition of those from the parent units. On the other hand, this additivity trend is not consistently observed for the NLO responses. However, an interpretation of these NLO responses has been proposed by using the unit sphere representation of the first hyperpolarizability tensors to address their orientational aspects as well as by resorting to the few-state approximation and the missing state analysis to highlight the localized or charge-transfer nature of the dominant excited states.

The construction of full-color fluorescence systems has received widespread attention because of their applications in lighting materials, optoelectronic materials, and fluorescent probes. However, for the full-color luminescence system based on trichromatic materials, there are no connections between materials of different luminescent colors. Herein, A new donor-acceptor dye with red fluorescence was synthesized. The dye displays excellent optical properties of short half-peak width and strong fluorescence emission. An effective energy transfer process from the dansyl donor to the acceptor was observed with a transfer efficiency of 81%. Further, dyes with green and blue fluorescence were introduced to construct a full-spectrum fluorescent system. Through exchange reactions of Diels-Alder dynamic covalent bonds, red, green, and blue luminescence can be converted. This work provides a new idea for the design of full-color fluorescent materials.