Soluble Diphenylhexatriene Dimers for Intramolecular Singlet Fission with High Triplet Energy

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Abstract
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(T1)similar to 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.
Funding Information
  • Engineering and Physical Sciences Research Council (EP/P007767/1, EP/S003126/1, EP/V055127/1)
  • Winton Programme for the Physics of Sustainability
  • Ramsay Memorial Trust

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