Does Inactive Alkyl Chain Enhance Triplet–Triplet Annihilation of 9,10-Diphenylanthracene Derivatives?

It has been hypothesized that alkyl chains are inactive for electron transport processes through the chains. However, our theoretical study unveiled that loop-like alkyl chains can accelerate the electron transfer of triplet–triplet annihilation (TTA) through overlap of the pseudo π-orbital of the alkyl chain. The TTA reaction time τ (the inverse of the TTA rate) of the dimer models of 9,10-diphenylanthracene (DPA) or the alkyl-strapped derivatives (C n -sDPAs) in a solution was calculated by the sequential charge transfer (SCT) processes of TTA with the Marcus theory. The τ for the C n -sDPAs were much shorter compared to that of DPA even at long distances and at various mutual orientations of the dimers. These shortened τ were due to the large electron coupling matrix elements through the pseudo-π-orbital that was extended to the alkyl chains in the singly occupied orbitals. This finding supports the observed superior performance of TTA upconversion obtained with C n -sDPAs.