Thermoluminescence Originating from the Singlet Excited State of 1,4‐Diarylcyclohexane‐1,4‐diyls: A Potentially General Strategy for the Observation of Short‐Lived Biradicals

Light from an unobservable source: Annealing a γ-irradiated glassy matrix containing 2,5-diaryl-1,5-hexadiene 1 gives rise to an intense thermoluminescence (TL) that is assigned to the singlet excited state of the corresponding cyclohexane-1,4-diyl (12..*) on the basis of substituent effects on λTL and DFT calculations (see picture showing thermoluminescence of 12..*; Ar=4-XC6H4; from left to right: X=F, H, Me, Cl, Br).