biostudies-literatureWu TDalian University of Technology4639-4645https://www.ebi.ac.uk/biostudies/studies/S-EPMC8694490biostudies-literatureUnknown11(8)Femtosecond fluorescence up-conversion and transient absorption pump-probe setups are applied to study the relaxation dynamics of the lower and upper excited singlet electronic states in easy-to-make rubrene films. Upon 250 nm (4.96 eV) excitation, singlet fission was observed directly from S₂ state bypassing S₁ state within 30 fs <i>i.e.</i> breaking the classical Kasha rule. From the transient absorption measurements, polaron formation was also detected on the same time scale. Both singlet fission and polaron formation are accelerated from upper excited states compared with S₁ state. Our work shows that rubrene films with low degree of crystallinity could display efficient singlet fission, notably in the case of excitation to upper lying electronic statesRSC advancesSinglet fission from upper excited singlet states and polaron formation in rubrene film.PMC8694490DUT18GJ205startupSun LGurzadyan GGNi WWu TfalseSinglet fission from upper excited singlet states and polaron formation in rubrene film.Femtosecond fluorescence up-conversion and transient absorption pump-probe setups are applied to study the relaxation dynamics of the lower and upper excited singlet electronic states in easy-to-make rubrene films. Upon 250 nm (4.96 eV) excitation, singlet fission was observed directly from S₂ state bypassing S₁ state within 30 fs <i>i.e.</i> breaking the classical Kasha rule. From the transient absorption measurements, polaron formation was also detected on the same time scale. Both singlet fission and polaron formation are accelerated from upper excited states compared with S₁ state. Our work shows that rubrene films with low degree of crystallinity could display efficient singlet fission, notably in the case of excitation to upper lying electronic states2021-01-01T00:00:00Z2021 Jan2025-04-22T09:58:23.256Z2025-04-05T23:21:25.876ZS-EPMC86944903542441310.1039/d0ra10780h