A possible route to the violation of Vavilov–Kasha rule in π-conjugated polymers

A possible route to the violation of Vavilov–Kasha rule in phenyl based π-conjugated polymers is proposed. We show that there exists ‘optically silent’ two photon states closed to the first excited two photon state in phenyl based π-conjugated polymers. Existence of such states explain why ultrafast internal conversion to the lowest optical state does not take place from the higher energy two photon state reached by photoinduced absorption. We propose that at least part of the charge carrier excitations from the higher energy two photon ,state decays to the ‘optically silent’ two photon state via intermediate energy one photon states (jBu) contributing to the violation of Vavilov–Kasha rule.