A Photophysical Study of Tri-chromophoric Systems Containing Two Naphthalene Moieties: Intramolecular Excimer Fluorescence, Energy Transfer, Phosphorescence, and Delayed Fluorescence

Abstract

Abstract Photophysical properties of 9,10-di[(l-naphthyl)-methyl]-9,10-dihydro-9,10-phenanthrenediol (1), 9,10-di(l-naphthyl)phenanthrene (2), 9,10-di(2-naphthyl) phenanthrene (3), 10,10-di(1 -naphthyI)- 9,10-dihydro-9-phenanthrone (5 a) and 10,10-di(2-naphthyl)-9,10-dihydro-9-phenanthrone (5 b) have been studied. In contrast to l,4-di(l-naphthyl)butane compound 1 shows strong (intramolecular) excimer fluorescence in dilute solution at room temperature. As a result of intramolecular triplettriplet energy transfer the phosphorescence of 2, 3, 5 a and 5 b stems from the naphthalene moieties. The increase (compared to naphthalene) of the rate constant of the radiative deactivation of the lowest triplet state is probably due in the case of 2 and 3 to the non-planarity of the molecules, which is expected to increase spin-orbit coupling, while in compounds 5 a and 5 b intramolecular chargetransfer interaction between the carbonyl group and the naphthalene moieties may be responsible for this effect. Delayed fluorescence (from the phenanthrene moiety) of 2 has been observed in fluid solution at room temperature, and an excitation mechanism is proposed