NOVEL GLASS-FORMING ORGANIC MATERIALS .2. STRUCTURE AND FLUORESCENCE OF PYRENE-CONTAINING AND CARBAZOLE-CONTAINING CYCLOHEXANE, BICYCLOOCTENE, AND ADAMANTANE

A series of novel glass-forming organic materials consisting of pyreny l and carbazolyl groups attached to cyclohexane with a 1-axial-2-equat orial configuration, bicyclo[2.2.2]oct-7-ene with an all-exo configura tion, and adamantane were synthesized and characterized. On the basis of proton NMR spectra, it was found that the rotation of pendant pyren yl and carbazolyl groups is restricted in the bicyclic system presumab ly because of steric hindrance in the all-exo configuration. In contra st, free rotation was found to prevail in cyclohexane- and adamantane- based systems. Fluorescence spectra gathered in solution at room tempe rature show evidence exclusively for intramolecular excimer formation in pyrene-containing compounds up to a concentration of 10(-4) M. On t he contrary, carbazole-containing compounds are not prone to excimer f ormation in the concentration range 10(-6)-10(-3) M, presumably becaus e of the more stringent requirements of interchromophoric distance and orientation. Although both pyrene and carbazole are highly crystallin e on their own, attachment to cyclic, bicyclic, and tricyclic central cores was found to contribute to an ease of vitrification of the hybri d systems with a T-g ranging from 43 to 132 degrees C. Moreover, the q uenched glasses of all seven model systems were found to possess morph ological stability in view of the absence of recrystallization upon he ating from 0 to 200 degrees C at a heating rate ranging from 0.2 to 20 degrees C/min. Morphological stability was further supported by the a bsence of recrystallization upon prolonged thermal annealing at temper atures above T-g.