Spectral properties of stilbazolium merocyanines oriented in stretched polymer films and Langmuir-Blodgett monolayers

Three stilbazolium merocyanines: 1-(6'-hydroxyhexyl)-4-[(4-oxocyclohexa-2,5 -dienylidene)ethylidene]-1,4-dihydropyridine; 1-(11'- hydroxyhexyl)-4-[(4-o xocyclohexa-2,5-dienylidene)ethylidene]-1-,4-dihydropyridine; 1-(10'-carbox ydecyl)4-[4-oxocyclohexa-2,5-dienylidene)ethylidene]-1,4-dihydropyridine sa lt HCl located in Langmuir-Blodgett monolayers and deposited on quartz plat e as well as embedded in isotropic or stretched polyvinyl alcohol films wer e investigated. Dyes occur in protonated and free-base forms. The concentra tion ratio of these forms depends on pH of subphase (for monolayers) or res in addition (in polymer film). The polarized absorption and fluorescence spectra were measured and coeffic ients of absorption and emission anisotropy were calculated. Dye molecules were in both matrices oriented, but degrees of orientation of various forms of dye were different. The anisotropies of absorption and emission are als o different which strongly suggests the occurrence of dye forms with differ ent yield of fluorescence and various orientations. The formation of mixed aggregates of protonated and free-base form is suggested. The orientation o f stilbazolium merocyanines in anisotropic matrix is important in the appli cation of these dyes as the sensors for measurements of the local electric field in biological membranes as well as for the formation polarizing absor ption polymer film used in some types of two-colours liquid crystal display s. (C) 2001 Elsevier Science B.V. All rights reserved.