Photochemical behaviour of tethered dianthryl compounds in sol–gel glass

Abstract

Sol–gel films and monoliths were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) or tetramethyl orthosilicate (TMOS) in the presence of 1,3-bis(9-anthryl)propan-1-ol (BAP), bis(9-anthrylmethyl)amine (BAA) and the intramolecular photodimer of BM (DBAA). The intramolecular photodimerization of these dianthryl compounds as photoprobes was examined in sol–gel glasses and compared with those in solutions as well as in poly(methyl methacrylate)(PMMA) films. The intramolecular photodimerization of both BAP and BAA was severely suppressed in sol–gel glasses and PMMA films to lead to exclusive photo-oxidization, indicating the steric restriction of these matrices. A marked difference in the matrix effect between the two solids was found in the reversible photodimerization of DBAA. Photogenerated anthryl units of DBAA disappeared upon exposure to 365 nm light faster in PMMA than in sol–gel silica, suggesting that the face-to-face conformation of photodissociated DBAA is more readily relaxed rather than in the inorganic matrix. This was supported by the fact that further exposure to 285 nm light gave a lower regeneration of anthryl units in the silica bulk material than in the PMMA matrices.