Pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as o-(Pc)2 and m-(Pc)2] were synthesized to examine intramolecular orientation-dependent multiexciton dynamics, especially focusing on the singlet fission (SF) and recombination from correlated triplet pairs (TT). Absorption and electrochemical measurements indicated strong intramolecular couplings of o-(Pc)2 relative to m-(Pc)2. Femtosecond and nanosecond transient absorption measurements successfully demonstrated the efficient SF in both dimers. In contrast, the dissociation process from the (TT) to the individual triplets [(2 × T)] was clearly observed in m-(Pc)2, which is in sharp contrast to a major recombination process in o-(Pc)2. Time-resolved electron spin resonance (TR-ESR) measurements demonstrated that the recombination and the dissociation proceed from quintet state of 5(TT) in m-(Pc)2. Rate constant of the SF was two orders of magnitude greater in o-(Pc)2 than that in m-(Pc)2 and were rationalized by enhanced electronic coupling between adjacent HOMOs of the Pc units.
ASJC Scopus subject areas
- Materials Science(all)