Synergetic Role of Conformational Flexibility and Electronic Coupling for Quantitative Intramolecular Singlet Fission

We present a novel design concept of molecular dimers for quantitative individual triplet yield (Φ_Τ) 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 Φ_Τ: 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 Φ_Τ was clarified.