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Photophysical Properties of Pyrazinocoumarin Derivatives
Author(s) -
Shim Sang Chul,
Han Gyu Seok
Publication year - 1997
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1997.tb08637.x
Subject(s) - phosphorescence , intersystem crossing , chemistry , fluorescence , photochemistry , absorption (acoustics) , absorption spectroscopy , point of zero charge , spectral line , analytical chemistry (journal) , excited state , materials science , atomic physics , physics , adsorption , singlet state , organic chemistry , optics , astronomy , composite material
Abstract Pyrazinocoumarin (PzC), 7‐methoxypyrazinocoumarin (7‐MOPzC) and 5,7‐dimethoxypyrazinocoumarin (5,7‐DMPzC) show the similar UV‐visible absorption spectra as the corresponding coumarins except for more distinct shoulders in the near UV absorption band (300–350 nm), probably due to n * transition. Fluorescence excitation spectra of PzC derivatives in nonpolar solvents have the lowest energy maxima in the region of the shoulders of UV‐visible absorption, indicating the lowest fluorescent state to have the same energy as these shoulders. Fluorescence quantum yields (ρF) of pyrazinocoumarins are on the order of 10 2‐10‐4, much lower than the corresponding coumarins. The activation energies (Ea(nr)) for nonradiative processes (internal conversion, intersystem crossing, etc.) determined by the temperature effect on the fluorescence are 10.2, 6.35 and 6.57 kj/mol for PzC, 7‐MOPzC and 5,7‐DMPzC, respectively. Phosphorescence emission spectra of PzC and 7‐MOPzC are structureless with φP of 0.12 and 0.17, respectively