Synergetic Role of Conformational Flexibility and Electronic Coupling for Quantitative Intramolecular Singlet Fission
Shunta Nakamura, Hayato Sakai, Hiroki Nagashima, Masaaki Fuki, Kakeru Onishi, Ramsha Khan, Yasuhiro Kobori, Nikolai V. Tkachenko, Taku Hasobe
Abstract
We present a novel design concept of molecular dimers for quantitative individual triplet yield (ΦΤ) through intramolecular singlet fission. We synthesized a series of tetracene (Tc) dimers bridged by different phenylene-based linkers, focusing on the conformational flexibility in addition to the electronic coupling. In transient absorption measurements, a 4,4′-biphenyl-bridged Tc dimer with weaker electronic coupling and larger conformational flexibility exhibited the quantitative ΦΤ: 196 ± 12% at high excitation energy. Moreover, decoupled spins associated with conformational change were directly characterized by time-resolved electron paramagnetic resonance. Strong interplay of the geometry change and electronic localization was revealed on the triplet pair dissociation through magnitudes of spin–spin exchange couplings. Thus, a synergetic role of conformational flexibility and electronic coupling in quantitative ΦΤ was clarified.