TRIPLET TO TRIPLET ABSORPTION IN ORGANIC MOLECULES FOR USE IN PHOTOCHROMIC DEVICES.

The report describes a continuing program of research whose aim is to investigate and evaluate new classes of triplet state photochromic materials. The work is centered upon studies of substituted aromatics and heterocyclic compounds. The effect of solvent composition upon fluorescence, phosphorescence and T-T absorption has been investigated for several compounds with the aim of determining the conditions for which the photochromic behavior of a compound will be maximized. Studies have been made for benzquinolines, dibenzacridines, 6 amino chrysene (I) and dibenzo(c, g)carbazole (II). Results of these studies are presented and discussed in terms of the solvent influence upon the lone pair of electrons on the nitrogen in aza-aromatics and for (I) and (II) in terms of a change in excited state properties compared to the ground state. The photochromic properties of several new compounds, including phenanthrolines and some oxygen containing hetercyclics; have been investigated. Results reveal one compound, 2,3 dimethyl; 1,4 phenanthroline, that shows good promise as a photochromic. Some uses of triplet state photochromics are discussed and conclusions of this work and recommendations for future studies are given. (Author)