Triplet-Pair Character of the $2^1{A}_g$ Dark State of Polyenes

Alexandru G. Ichert, William Barford

We define and calculate the triplet-pair population of the $2^1{A}_g$ dark state in polyenes, as predicted by the $\pi$-electron Pariser-Parr-Pople (PPP) model, for chains of 8 to 14 C…