Heavy Atom Effect's Influence on the Triplet State and Upconversion Efficiency in MR-TADF Systems
Multi-resonance thermally activated delayed fluorescence(MR-TADF)containing heavy atoms exhibits low energy loss,intense absorption,high intersystem crossing(ISC)efficiency,and long triplet state lifetime.In this work,three heavy metal-free MR-TADF molecules combined oxygen,sulfur,and selenium atoms were chosen,designated as BN-2O,BN-2S,and BN-2Se.The heavy atom effect of these compounds was studied using theoretical calculations and nanosecond transient absorption spectra.The ISC efficiencies of BN-2O,BN-2S,and BN-2Se are determined to be 39.4％,74.7％,and 95.0％,respectively,while the triplet state lifetimes are found to exceed 10 μs.The upconversion system comprising BN-2Se/l,4-bis(triisopropylsilethynyl)naphthalene(1,4-DTNA)demonstrates a high upconversion quantum yield(ΦUC,the maximum value of 50％)of up to 8.7％in solution,with a threshold excitation intensity as low as 1.7 mW/cm2,which is lower than the solar irradiance of 2.7 mW/cm2.Additionally,the economically viable BN-2S and BN-2O show satisfactory ΦUCvalues of 5.9％and 3.9％,with low Ith values of 6.2 and 15 mW/cm2.
Multi-resonance thermally activated delayed fluorescenceTriplet-triplet annihilation upconversionHeavy atom effect
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维普
