[en] The photophysical properties of N-butyl-4-hydroxyl-1, 8-naphthalimide (BOH) and N-(morpholinoethyl)−4-hydroxy-1, 8-naphthalimide (MOH) in various solvents are presented and the density functional theory (DFT)/time-dependent density functional theory (TDDFT) methods at the B3LYP/TZVP theoretical level are adopted to investigate the UV–visible absorption and emission data. An efficient intermolecular excited-state proton transfer (ESPT) reaction occurs for both compounds in DMSO, methanol and water. In aqueous solution, both BOH and MOH can be used as ratiometric pH probes and perform as strong photoacids with pKa*=−2.2, −2.4, respectively. Most interestingly, in the steady-state fluorescence spectra of BOH and MOH in concentrated HCl, an unexpected blue-shifted band is observed and assumed to originate from the contact ion pair (CIP) formed by hydronium ion and the anionic form of the photoacid resulted from ESPT. Theoretical calculations are used to simulate the CIP in the case of BOH, which afford reasonable results compared with the experimental data.

[en] The quantum reactive scattering dynamics calculations are carried out over the collision energy range of 0-1.0 eV on the double many-body expansion (DMBE) potential energy surface reported by Poveda and Varandas [Phys. Chem. Chem. Phys. 7 (2005) 2867]. The reaction probabilities, integral cross-section and rate constants for the title reaction are calculated. The calculated rate constants are in agreement with the available experimental results at high temperature but lower than the experimental results at low temperature. (authors)

[en] Highlights: • The different synthetic routes of 1-Methyl-2,4,5-trinitroimidazole (MTNI) was studied in detail by using DFT method. • The nitration reaction path is affected by the solvent molecule. • The yield is affected by the different nitration mechanisms. During the synthesis of 1-methyl-2,4,5-trinitroimidazole (MTNI), the product yield was affected by group introduction order. This phenomenon has not been explained in the reaction mechanism. In this paper, the DFT method was used to study the synthesis mechanism. For the nitration reaction, an N-H$\cdots$O hydrogen bond was formed between the midazole ring and water molecule in the solution to promote the nitration reaction, so the nitration mechanism was affected by the introduction of methyl group at the N site. For the methylation reaction, the electrophilic attack of the methyl group was affected by the introduction of more electron-withdrawing nitro group.

[en] The goal of this study is to develop a novel 5-HT_1A receptor imaging agent. 4-[(2-methoxyphenyl)piperazin-1-yl]-dithioformate (MPPDTF) was labeled with ^99mTc-tricarbonyl core via dithioformate moiety in high yield (>96% by HPLC). ^99mTc(CO)₃-MPPDTF is a neutral and lipophilic complex, which was confirmed by paper electrophoresis and octanol/water partition coefficient (P=27.0±1.4, n=3), respectively. In vivo biodistribution indicated that this complex had moderate brain uptake (0.53±0.10% ID/g at 5 min and 0.42±0.02% ID/g at 120 min) and good retention (about 80% of the activity was retained in the brain at 120 min post-injection). Regional brain distribution study showed that hippocampus, where the 5-HT_1A receptor density is high, had the highest uptake (0.60±0.02% ID/g at 5 min p.i.) and the cerebellum, where the 5-HT_1A receptor density is low, had the lowest uptake (0.10±0.02% ID/g at 5 min p.i.). After blocking with 8-OH-DPAT, the hippocampus uptake was decreased obviously while the cerebellum uptake was increased slightly. This result indicates that ^99mTc(CO)₃-MPPDTF complex has specific binding to 5-HT_1A receptor

[en] Lead-free halide perovskites have triggered interest in the field of optoelectronics and photocatalysis because of their low toxicity, and tunable optical and charge-carrier properties. From an application point of view, it is desirable to develop stable multifunctional lead-free halide perovskites. We have developed a series of Cs${}_2$Pt${}_x$Sn${}_{1-<!--\; ???\; -->x}$Cl${}_6$ perovskites (0≤x≤1) with high stability, which show switchable photoluminescence and photocatalytic functions by varying the amount of Pt${}^{4+}$ substitution. A Cs${}_2$Pt${}_x$Sn${}_{1-<!--\; ???\; -->x}$Cl${}_6$ solid solution with a dominant proportion of Pt${}^{4+}$ shows broadband photoluminescence with a lifetime on the microsecond timescale. A Cs${}_2$Pt${}_x$Sn${}_{1-<!--\; ???\; -->x}$Cl${}_6$ solid solution with a small amount of Pt${}^{4+}$ substitution exhibits photocatalytic hydrogen evolution activity. An optical spectroscopy study reveals that the switch between photoluminescence and photocatalysis functions is controlled by sub-band gap states. Our finding provides a new way to develop lead-free multifunctional halide perovskites with high stability. (© 2021 Wiley‐VCH GmbH)

[en] The rotational reorientation dynamics of rhodamine 700 (LD700) in the first (S₁) and the fifth (S₅) excited state in three aprotic polar solvents have been investigated using femtosecond time-resolved stimulated emission pumping fluorescence depletion (FS TR SEP TD) spectroscopy. In both excited states, the overall rotational relaxation of LD700 occurs on a time scale of 40-230 ps depending on the solvent, and a quantitative analysis of this time constant has been performed using the Stokes-Einstein-Debye (SED) hydrodynamic theory combined with the extended charge distribution model developed by Alavi and Waldeck. The experimentally measured reorientation times for LD700 in S₅ are smaller than those in S₁, which is in accord with the predictions by the SED theory. In addition, for LD700 in S₅, a rapid initial decrease on the time scale less than 0.5 ps has been found. According to our analysis, this fast component may account for the rapid internal conversion from S₅ to S₁, and the rate of internal conversion was found to be sensitive to the solvent polarity

[en] Triplet exciton-based long-lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self-trapped excitons to Mn${}^{2+}$ dopants in solution-processed perovskite CsCdCl${}_3$. It is found the Mn${}^{2+}$ doped hexagonal phase CsCdCl${}_3$ could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti-thermal quenching from 300 to 400 K. In-depth charge-carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl${}_6$]${}^{4-<!--\; ???\; -->}$) is responsible for the afterglow emission with anti-thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications. (© 2022 Wiley‐VCH GmbH)

[en] Subpicosecond fluorescence depletion spectroscopy (FDS) was used to measure the solvation dynamics of coumarin 153 (C153) in methanol. The FDS mechanisms were discussed. A quasi-continuous model was used to describe the solvational relaxation of excited states. The perturbations of the probe pulse on the excited sample system, including up-conversion and stimulated emission, were sufficiently discussed. For a probe molecule used in the FDS experiment, ensuring that the up-conversion perturbation can be negligible is important. FDS was found to be a good technique for measuring the solvation dynamics of C153 in methanol. - Highlights: ► Mechanisms of subpicosecond fluorescence depletion spectroscopy. ► Quasi-continuous model was used to describe the solvational relaxation. ► The solvation dynamics of coumarin 153 in methanol has been measured.