Singlet exciton fission dynamics in 6,13-diphenylpentacene nanoaggregate and thin film

Abstract

Pentacene is the archetypal example of singlet fission material in polyacene family with fastest known singlet fission rate (τ_SF <100 fs). However, pentacene suffers from fast chemical and photochemical degradation in ambient condition, mainly by oxidation at 6 and 13-positon and hence limits prospects in optoelectronic application. Herein we show phenyl substituted pentacene at 6 and 13 position offers improved photo-stability with preserved SF property. Detailed transient pump-probe spectroscopic investigation on 6,13-diphenylpentacene (DPPn) thin film and nanoaggregates shows efficient singlet exciton fission process occurring in tens of picosecond timescale. In comparison to pentacene, though SF rate in DPPn is observed to slow down about two orders of magnitude due to weaker electronic coupling imposed by two phenyl substitution, triplet yield remains attractively high (∼ 180 %). Remarkably, thermal and photochemical stability of the DPPn thin film (remains stable over several months in ambient condition) is observed to be much superior than pentacene and thus proposed to be more useful for practical application in optoelectronic devices.