Excited-state intramolecular proton transfer and spectroscopy of 2-(2'-hydroxyphenyl)benzoxazole in solid polymer matrices

This paper first reports the spectroscopy and the properties of excited-state intramolecular proton transfer (ESIPT) of 2-(2'-hydroxy phenyl)benzoxazole (HBO) in some solid polymer matrices and the matix effects on them. The results show that: (1) The properties of ESIPT and spectra of HBO in the non-polar and weak polar polymer matrices would not be modified compared with those in the solution systems. The matrices, on the other hand, could improve the quantum yield of ESIPT fluorescence. (2) The polymer matrices with strong H-bonding activity and polarity can modify the spectra and the ESIPT efficiency of HBO due to the formation of H-bonding complex between HBO and the matrix, which, however, could be eliminated effectively by using a special micelle method to isolate HBO from the matrices. (3) Thermodynamic equilibrium of the ground state rotamers of HBO in the solid polymer matrices seems to have a tendency which is unfavourable to the formation of the rotamer I and II.