The S0-T1 transition of [1.1.1]propellane: a theoretical study

The lowest energy vibro-electronic transition, S0-T1, of [1.1.1]propellane is studied by a combination of ab initio molecular orbital and density functional theory methods together with Franck-Condon model calculations. To avoid a possible bias in the simulation of the vibrational envelope, the accuracy of the ground state parameters is assessed through a comparison with experimental results. At odds with the behaviour of unsaturated carbon systems, where electron excitation usually promotes bond elongation and/or torsion, the T1 state of [1.1.1]propellane undergoes cleavage of the central bond. The possible implications of this behaviour are discussed.