1 research outputs found
Multiexciton Dynamics Depending on Intramolecular Orientations in Pentacene Dimers: Recombination and Dissociation of Correlated Triplet Pairs
Pentacene
dimers bridged by a phenylene at ortho and meta positions
[denoted as <i>o</i>-(Pc)<sub>2</sub> and <i>m</i>-(Pc)<sub>2</sub>] were synthesized to examine intramolecular orientation-dependent
multiexciton dynamics, especially focusing on singlet fission (SF)
and recombination from correlated triplet pairs [(TT)]. Absorption
and electrochemical measurements indicated strong intramolecular couplings
of <i>o</i>-(Pc)<sub>2</sub> relative to <i>m</i>-(Pc)<sub>2</sub>. Femtosecond and nanosecond TA measurements successfully
demonstrated efficient SF in both dimers. In contrast, the dissociation
process from the (TT) to the individual triplets [(2 × T)] was
clearly observed in <i>m</i>-(Pc)<sub>2</sub>, which is
in sharp contrast to a major recombination process in <i>o</i>-(Pc)<sub>2</sub>. Time-resolved electron spin resonance (TR-ESR)
measurements demonstrated that the recombination and dissociation
proceed from the quintet state of <sup>5</sup>(TT) in <i>m</i>-(Pc)<sub>2</sub>. The rate constant of the SF was 2 orders of magnitude
greater in <i>o</i>-(Pc)<sub>2</sub> than that in <i>m</i>-(Pc)<sub>2</sub> and was rationalized by enhanced electronic
coupling between adjacent HOMOs of the Pc units