PREPARATION AND CHARACTERIZATION OF MIXED THIN-FILMS CONTAINING SPIROPYRANS AND LONG-CHAIN ALKYL SILANES - TOWARDS A COMMAND SURFACE FOR LIQUID-CRYSTAL REALIGNMENT

Spiropyran derivatives containing variable-length linking chains and e ither tri- or mono-alkoxysilane end groups were synthesized. Thin film s on glass slides were formed with mixture of the spiropyran compounds and either octadecyltrimethoxysilane or octadecyldimethylmethoxysilan e. The photochemistry of the spiropyran in the films was investigated by UV-Vis spectroscopy. Irradiation forms the merocyanine, which is de tected by absorption spectroscopy. The rate of the thermal reversion o f the merocyanine to the spiropyran was studied and found to show no d ependence on chain length and resemble that found in solid polymers, n ot solution. Sessile drop contact angle measurements show a decrease f rom 70 +/- 3 to 63 +/- 2 degrees for films prepared from 4, and a drop from 50 to 46 +/- 2 degrees for films prepared from 6 upon irradiatio n with UV light. Evaluation of this system as a surface to control the realignment of the nematic liquid crystal in a nematic liquid crystal proved unsuccessful, though the surface energy of the system can be c hanged solely by irradiation with light. (C) 1998 Elsevier Science Lim ited.