Photo-orientation movement of photoisomerizable chromophores: quantifying analytical theory and application to spectrally overlapping and distinguishable isomers

摘要

We introduce the analytical theory of coupled photoisomerization and photo-orientation both for individualizable and spectrally overlapping isomers, and we use it to quantify the photo-orientation movement of chromophores in polymers including photoisomerization quantum yields. We study photo-orientation processes in A <-> B photoiosmerizable systems where B is unknown. We contrast systems where the isomers are individualizable and without and with thermal A<-B respectively, and systems of nondistinguishable isomers, namely push-pull azobenzenes attached to polyurethane polymers. When diarylethenes and spiropyrans are oriented by polarized excitation, the apparent optical orientation changes sign for the ultra-violet versus the visible photochemical transitions; a feature which is due to perpendicular transition dipoles of the B isomer of these chromophores Photo=orientation reveals the symmetry nature of photoisomerization transitions. We also report on the observation of near-pure photo-orientation by photosiomerization of azo dye in polymers; an observation which is attributed to both the particular molecular structure of the polymer studied and to approprate photoisomerization quantum yields as well as a fast trans<- cis thermal isomerization, and is rationalized by the study of photo-orientation of a series of azo-polyurethanes each with distinct differences in the molecular structure of the unit building blocks.