- CHEMICAL SOC JAPAN
The photochemistry of 2-(2-hydroxy-3-methoxyphenyl)benzoxazole (3-MHBO) and 2-(2-hydroxy-4-methoxyphenyl)benzoxazole (4-MHBO) have been investigated. The excited-state properties of 4-MHBO were similar to those for the parent compound 2-(2-hydroxyphenyl)benzoxazole (HBO), whereas different properties were observed for 3-MHBO. 4-MHBO in benzene exhibited large Stokes-shifted fluorescence from the keto-form in the excited singlet state (K-E*) after excited-state intramolecular proton transfer (ESIPT), whereas 3-MHBO emitted dual fluorescence from E* and K-E* species. Fluorescence due to K-E* for 3-MHBO (lambda(max) = 525 nm) occurred at a considerably longer wavelength than that of 4-MHBO (lambda(max) = 480 nm). The fluorescence efficiency of 3-MHBO (Phi(f) = 0.002) was much smaller than those of 4-MHBO and HBO (Phi(f) = 0.0 18 and 0.02, respectively). These results are consistent with suppression of ESIPT, stabilization of K-E* species, and acceleration of non-radiative decay, probably because of the formation of a hydrogen bond between phenol oxygen and methoxy hydrogen at 3-position in 3-MHBO. Thus, 3-MHBO displayed a meta-substituent effect involving the relaxation pathway of excited state HBO derivatives.
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- DOI : 10.1246/bcsj.80.561
- ISSN : 0009-2673
- eISSN : 1348-0634
- Web of Science ID : WOS:000245885000020