A variety of 3,7‐substituted 9 H ‐quinolino[3,2,1‐ kl ]phenothiazin‐9‐one (QPO) and 9 H ‐quinolino[3,2,1‐ kl ]phenothiazin‐9‐one 5,5‐dioxide (QP3O) derivatives were synthesized via Suzuki coupling in moderate to quantitative yields (54%–99%) to investigate the influence of oxidation and substitution on the electronic structure and photophysical properties on this scaffold. Photophysical studies reveal a markedly different substituent sensitivity for the two core structures: while the QPO derivatives exhibit largely similar emission characteristics without pronounced influence of the substituents and quantum yields of up to 0.50 in solution and 0.25 in the solid state, the oxidized QP3O derivatives show a pronounced dependance on the electronic nature of the substituents, reaching quantum yields of up to 0.42 in solution and 0.31 in the solid state. Quantum chemical calculations reveal a competition between fluorescence decay and intersystem crossing in these compounds and indicate an increased involvement of the substituents in the excited‐state electronic structure of the QP3O derivatives. The oxidation to QP3O is further accompanied by a blueshift in emission, reduced Stokes shifts, and narrower emission bands (FWHMs), highlighting the impact of structural modification on the emissive properties. These results provide detailed insight into structure–property relationships in quinolino‐phenothiazine systems and establish design principles for tuning their photophysical behavior.
Luminescent N , O ‐chelated boron complexes are promising fluorescent materials owing to their rigid molecular structures and favorable photophysical properties. In this study, a series of luminescent N , O ‐chelated benzimidazole‐based boron complexes were synthesized, and their photophysical properties and excited‐state dynamics were systematically investigated by steady‐state and time‐resolved spectroscopic studies, supported by theoretical calculations. The complexes exhibited bright blue fluorescence with photoluminescence quantum yields of up to 0.76, whereas their absorption and emission properties were only slightly affected by the electronic nature of the boron‐bound aryl substituents. The calculations revealed that the lowest‐energy absorption originates predominantly from the HOMO→LUMO transition, while transient absorption spectroscopy provided insight into the excited‐state relaxation pathway. Representative complex 2a exhibited low cytotoxicity and preferential mitochondrial localization, suggesting its potential as a fluorescent probe for mitochondrial imaging.
Two-photon excitation of fluorescence dyes and proteins is widely used for imaging living systems due to reduced scattering in biological media. Two-photon absorption properties are well-studied, but there is very little known on two-photon reaction dynamics. Here, we present time-resolved vibrational spectroscopy upon one- and two-photon excitation at 515 and 1030 nm, respectively, on 4-(dicyano-methylen)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) in dimethyl-sulfoxide (DMSO) and tetrahydrofuran (THF) solvent. We demonstrate overall similar dynamics for both excitation regimes at about 4 and 300 GW/cm2. Vibrational dynamics of nitrile stretching demonstrate small conformational changes within 0.4 ps in both solvents and an additional conformational change within 1 ps in DMSO. This new method provides detailed information on vibrational properties in the electronic excited state, fosters our understanding and use of two-photon spectroscopy.
Photocatalytic water oxidation systems employing [RuII(bpy)3]2+ as a photosensitizer and S2O8 2- as a sacrificial electron acceptor are widely used to evaluate the activity of various catalysts. However, the stoichiometric amount of O2 hardly evolves due to the decomposition of [RuII(bpy)3]2+ during the reaction. We report herein that the addition of 5-20 vol% of acetonitrile (CH3CN) to the reaction solution increases the O2 yield irrespective of water oxidation catalysts (WOCs). For example, the addition of 20 vol% of CH3CN increased the O2 yield from 38% to 93% in a borate buffer containing [RuII(bpy)3]2+, S2O8 2- and a cobalt porphyrin complex working as a homogeneous WOC. An investigation into the effect of organic-solvent addition on each reaction step indicated that the oxidative decomposition of [RuII(bpy)3]2+ observed in a buffer without organic solvents was suppressed by the sacrificial oxidation of the organic solvents. In the presence of a WOC, the oxidation of MeOH and acetone more readily proceeds than water oxidation, resulting in low O2 yields. In contrast, the lower oxidation susceptibility of CH3CN scarcely interfered with water oxidation, thereby affording high O2 yields. CH3CN addition to the reaction solution is promising for the evaluation of intrinsic catalysis of each WOC.
A new coumarin-based probe, HL1, was designed and characterized using a variety of spectroscopic methods, including NMR, IR, UV, and mass spectrometry. A solvent-dependent study of the probe HL1 was done to understand the interaction of solvent with the probe in the ground and excited states. In H2O, DMF, DMSO, and MeOH solvents, the probe HL1 was shown to be extremely selective for 1,3-diaminopropane (DAP), acting as a turn-on fluorescent chemosensor. The probe's LOD allowed it to detect DAP preferentially in DMSO (0.22 & micro;M), DMF (0.21 & micro;M), MeOH (0.24 & micro;M), and water (0.16 & micro;M). Cyclized DAP-adduct exhibits a "turn-on" response in comparison to other diamines due to chelation-induced enhanced fluorescence and generation of an intramolecular charge transfer process. In addition to amine sensing, the HL1-DAP system effectively detected hazardous hydrazine with LOD and LOQ values of 0.17 and 0.59 & micro;M, respectively. The decrease in K-SV value with an increase in temperature indicates the presence of static quenching. The DFT and TD-DFT calculations reveal that the DAP-adduct formation increases the HOMO-LUMO energy gap, confirming the suppression of nonradiative pathways. Moreover, real-time, on-site DAP detection was demonstrated using paper strips, silica gel, vapor, soil, and water samples, validating the probe's usefulness in real applications.
