Soluble Diphenylhexatriene Dimers for Intramolecular Singlet Fission with High Triplet Energy
Oliver Millington, Stephanie Montanaro, Anastasia Leventis, Ashish Sharma, Simon Dowland, Nipun Sawhney, Kealan J. Fallon, Weixuan Zeng, Daniel G. Congrave, Andrew J. Musser, Akshay Rao, Hugo Bronstein
Abstract
High Resolution Image Download MS PowerPoint Slide Intramolecular singlet fission (iSF) facilitates single-molecule exciton multiplication, converting an excited singlet state to a pair of triplet states within a single molecule. A critical parameter in determining the feasibility of SF-enhanced photovoltaic designs is the triplet energy; many existing iSF materials have triplet energies too low for efficient transfer to silicon via a photon multiplier scheme. In this work, a series of six novel dimers based upon the high-triplet-energy, SF-active chromophore, 1,6-diphenyl-1,3,5-hexatriene (DPH) [ E (T 1 ) ∼ 1.5 eV], were designed, synthesized, and characterized. Transient absorption spectroscopy and fluorescence lifetime studies reveal that five of the dimers display iSF activity, with time constants for singlet fission varying between 7 ± 2 ps and 2.2 ± 0.2 ns and a high triplet yield of 163 ± 63% in the best-performing dimer. A strong dependence of the rate of fission on the coupling geometry is demonstrated. For optimized iSF behavior, close spatial proximity and minimal through-bond communication are found to be crucial for balancing the rate of SF against the reverse recombination process.