Nanoparticle Size-Dependent Singlet Fission and Exciton Dynamics in Amorphous TIPS-Pentacene

Aqueous nanoparticle (NP) dispersions are commonly used as model systems for spectro- scopic study of singlet exciton fission (SF) in acenes such 6,13-(triisopropylsilylethynyl) pentacene (TIPS-Pn). However, the potential particle size effects to complicate interpretation results is generally ignored. In this work, we amorphous TIPS-Pn NP prepared by re-precipitation method over a range sizes. Time-resolved fluorescence and femtosecond transient absorption spectroscopy show that dynamics these depend significantly upon size. Kinetic analysis reveals SF becomes slower at smaller sizes, while triplet decay (through both correlated pair relaxation geminate triplet-triplet annihilation) accelerates. These significant size-dependent ascribed increased morphological disorder within NPs, weakening intermolecular couplings which control migration. A non-radiative quenching channel separate from also identified, has not been previously reported NPs SF-capable chromophores. This pathway small substantially reducing yields. Interestingly, kinetics 81-nm approach those bulk TIPS-Pn, suggesting or larger likely good models TIPS-Pn. work demonstrates particle-size chromophores, must be accounted order accurately materials with dispersions.