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The Effect of Steric Hindrance on Triplet-Triplet Energy Transfer Rates: A Predictive Model Based on
Jiahui Cheng1, Ying Li1, Cheng Yang1
1Anhui Province Key Laboratory for Control and Applications of Optoelectronic Information Materials, School of Physics and Optoelectronics, Anhui Normal University, Wuhu241002, P. R. China.
Abstract:
Triplet-triplet energy transfer (TTET) via the Dexter mechanism is central to many photochemical applications, yet a quantitative structure-kinetic relationship for bimolecular quenching rate constants (kq) is still lacking. Here, using two photosensitizers and a series of anthracene-based acceptors with tailored steric profiles, we systematically investigate how nonconjugated substituents regulate kq. The most significant results are when the triplet energy gap exceeds ∼0.2 eV, kq is governed solely by steric hindrance and the suppression originates from spin-density-free units that block donor-acceptor wave function overlap. We establish a quantitative model in which the effective collision probability η equals the product of the van der Waals surface fractions carrying triplet spin density (P) for both donor and acceptor, giving kq,calc = kdiffuse × η. Predicted rates match experimental values well and are further validated against literature systems.
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