A simple model for linear polyene electronic structure

A simple model based on Huckel theory for interpreting linear polyene electronic structure is presented. The essential ingredients are the use of alternating resonance integrals to obtain the proper chain-length dependence of the 1 1Bu highest occupied molecular orbital (HOMO) to lowest unoccupied molecular orbital (LUMO) excitation energy and mixing of the HOMO to LUMO+1 and HOMO to LUMO double-excitation configurations to properly describe the 2 1Ag state. With the proper choice of parameters, this model reproduces all 25 2 1Ag and 1 1Bu 0–0 excitation energies that have thus far been measured for linear polyenes in low-temperature hydrocarbon solutions.