Intramolecular Singlet Fission in Pentacene Oligomers via an Intermediate State

Intramolecularsinglet fission (iSF) is an efficient strategy ofmultiexciton generation via a singlet exciton splitting into a correlatedtriplet pair in one organic molecule with more than two chromophores.Propeller-shaped iptycene-linked triisopropylsilyl-(TIPS)-ethynyl functionalizedpentacene oligomers (pent-monomer, pent-dimer, and pent-trimer) weresynthesized, and the iSF dynamics of pent-dimer and -trimer were monitoredby a visible-near-IR transient absorption (TA) spectroscopy.Quantum yields of the triplet pair, similar to 80%, of both estimatedby near-IR TA spectral analysis are in good agreement with the resultsof global analysis and triplet sensitization experiments. The iSFrate of pent-trimer is slightly faster than that of pent-dimer evenwith one more chromophore site. The unexpectedly weak difference indicatesthe existence of an intermediate process to realize iSF. The intermediateprocess might be determined by through-bond electronic coupling ofthe homoconjugation bridge in the pentacene oligomers. Our resultssuggest the importance of the rigid bridge to the fast iSF rate andthe elongated lifetime of the correlated triplet pair in pentaceneoligomers.