SOLID STATE ELECTRONIC SPECTRA OF RETENOIC ACID CRYSTALS

Abstract

Polarized low-temperature absorption, excitation and emission spectra of single crystals of all-trans retenoic acid will be discussed. Both the monoclinic form and a form optically identical to the triclinic modification have been investigated. These results can be interpreted with reference to the known crystal structure to establishthat the main absorption and emission are polarized along the conjugated chain. The crystal results are consistent with photoselection experiments and indicate that the absorption and emission are of $\pi\pi^{*}$ character. Further quantitative interpretation of the single crystal results in terms of the electronic structure of the free molecule will be presented.