Radiationless transitions in linear polyenes

Electronic radiationless transitions in linear polyenes are discussed from a theoretical point of view. Only in-plane relaxation is considered. It is concluded that for a given energy gap, the nonradiative decay rate is a decreasing function of the chain length. Model calculations of the nonradiative lifetime as a function of the polyene chain length are presented. For those cases where comparison with the experiment is possible (8 to 12 membered polyenes) agreement with the calculations is reasonable. The decrease in the rate of radiationless transitions with the increase in the molecular system is shown to have implications for biological systems, such as rhodopsin, that undergo a fast photochemical change.