Steric Effects in the Electronic Spectra of the3,5-Diarylaminobenzene Derivatives

Electronic spectral properties o f polyphenyls, in particular terphenyls, have been a subject o f numerous studies [1 -5 ] . In 1985 a new and efficient method o f the synthesis o f 3,5-diarylaminobenzenes and their derivatives was developed by Sepioi and Milart [6], Some fluorescent compounds belonging to this group, presented in Fig. 1, were chosen as a model set for the investigation o f several important photophysical problems; 1. What are the conformations o f the side aryls in the ground and excited states and how are they influenced by the presence of the methyl group in the X position (see Figure 1)? 2. What is the influence o f the nitrile groups on the spectral properties o f 3,5-diarylaminobenzenes? 3. What is the role o f the size (naphthyl vs. phenyl) and the mode o f binding (a-naphthyl vs. ^-naphthyl) o f the side aryl substituents? 4. How does the electronic excitation influence the charge distribution in such compounds? In order to answer these questions, absorption and fluorescence properties, fluorescence lifetimes and quantum yields o f the compounds shown in Fig. 1 were studied in three solvents o f different polarity (cyclohexane, methanol and acetonitrile) at concentrations o f 5 • 10-5 M. Some o f the absorption spectra were already reported [6 -8 ] .