Ultrafast excited-state dynamics of the simplest nitrostilbenes, namely -4-nitrostilbene (-NSB), was studied in solvents of various polarities with ultrafast broadband time-resolved fluorescence and transient absorption spectroscopies, and by quantum-chemical computations. The results revealed that the initially excited S(ππ*) state deactivation dynamics is strongly influenced by the solvent polarity. Specifically, the -NSB S-state lifetime decreases by three orders of magnitude from ∼60 ps in high-polarity solvents to ∼60 fs in nonpolar solvents. The strong solvent-polarity dependence arises from the differences in dipole moments among the S and relevant states, including the major intersystem crossing (ISC) receiver triplet states, and therefore, the solvent polarity can modulate their relative energies and ISC rates. In nonpolar solvents, the sub-100 fs lifetime is due to a combination of efficient ISC and internal conversion. In medium-polarity solvents, the S-state population decays a competing ISC relaxation mechanism in a biphasic manner, and the ISC rates are found to obey the inverse energy gap law of the strong coupling case. In high-polarity solvents, the S state is stabilized to a much lower energy such that ISC becomes energetically infeasible, and the S state decays barrier crossing along the torsion angle of the central ethylenic bond to the nonfluorescent perpendicular configuration. Regardless of the initial S-state deactivation pathways in various solvents, the excited-state population is ultimately trapped in the metastable T-state perpendicular configuration, at which a slower ISC occurs to bring the system to the ground state and bifurcate into either or form of NSB.
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http://dx.doi.org/10.1039/d3cp05245a | DOI Listing |
J Fluoresc
December 2024
Department of Chemistry, Sant Longowal Institute of Engineering & Technology, Longowal (Sangrur), Punjab, 148106, India.
This study reports the rapid intramolecular proton transfer studies upon photo excitation of 2-(benzo[d]thiazol-2-yl)naphthalene-1-ol derivatives, yielding tautomer emission with large Stokes shift. Employing photophysical studies, density functional theory (DFT) and, time-dependent density functional theory (TD-DFT) methods, we scrutinize excited state intramolecular proton transfer (ESIPT) modulation over varying solvent polarities. Analysis of UV-Visible and fluorescence spectra, alongside exploration of hydrogen bond dynamics, reveals solvation effects on the excited state proton transfer process.
View Article and Find Full Text PDFJ Mol Model
December 2024
Department of Chemistry, Faculty of Science, Ege University, TR-35100, Bornova, Izmir, Türkiye.
Context: Isatin-Schiff bases have wide applications in chemistry. The π conjugated electronic system and heterocylic structure of these materials make them valuable for use as photosensitized materials. The delocalization of π-electrons throughout the structure causes the UV-vis absorption spectra to shift to longer wavelengths.
View Article and Find Full Text PDFChem Sci
November 2024
Department of Chemistry, Indian Institute of Technology Kanpur Kanpur - 208 016 UP India +91 512 259 6806 +91 512 259 6312.
Heliyon
November 2024
School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, 4000, South Africa.
The aim of this research was to provide valuable insights on symmetrical α,β-unsaturated ketones as potential chemical ultraviolet (UV) filters from experimental data and theoretical aspects. Towards this end, density functional theory (DFT/B3LYP) calculations on a series of symmetrical α,β-unsaturated ketones, ()-1,5-bis[4-(R)phenyl]penta-1,4-diene-3-one (R = methylthio, ; R = dimethylamino, ; R = ethyl, ), were performed to determine the effect of different electron-donating substituents on their stability when exposed to solar UV radiation. Their molecular structures, and UV-visible, infrared (IR) and NMR (H and C) spectra were theoretically obtained from their optimized geometries with the B3LYP/6-311++ G (d, p) basis set and were compared with the experimental results.
View Article and Find Full Text PDFJ Phys Chem B
November 2024
Department of Bioengineering, University of California, Riverside, California 92521, United States.
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