Theoretical Study of the Intramolecular Localization and Migration of a Triplet Exciton in the N,N′-Di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) Molecule
By Ilya D. Krysko Alexandra Y. Freidzon Alexander A. Bagaturyants
The intramolecular localization and migration of a triplet exciton in the N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) molecule is studied by the XMCQDPT/CASSCF method. Energy profiles corresponding to linear interpolations between different localized states show that the barriers between minima are comparable with the vibrational energies of the soft modes corresponding to the transition of one structure to another. The triplet exciton lifetimes and characteristic migration times are estimated. It is shown that the intramolecular migration is 3 orders of magnitude faster than the main triplet decay process in α-NPD, namely, nonradiative deactivation. Therefore, at room temperature, the excitons can freely migrate over the molecule and become effectively delocalized during their lifetime.