Access to an excited state via the thermal ring-opening of a cyclopropylidene

(Equation Presented) Thermal generation of singlet excited states is unusual in organic chemistry. The potential energy surface for the thermal ring-opening of 4-methylene-bicyclo[3.1.0]hex-2-ene-6-ylidene (1) was calculated at the CASSCF level of theory and found to produce α,3-didehydrotoluene in its biradical ground state (S₀) and/or its zwitterionic excited state (S₁).