Asuka Ohshima, M. Ikegami, Y. Shinohara
Mar 13, 2007
Citations
0
Influential Citations
20
Citations
Journal
Bulletin of the Chemical Society of Japan
Abstract
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 (λ max = 525 nm) occurred at a considerably longer wavelength than that of 4-MHBO (λ max = 480nm). The fluorescence efficiency of 3-MHBO (Φ f = 0.002) was much smaller than those of 4-MHBO and HBO (Φ f = 0.018 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.