How important is the resonance formula 1′ for describing the properties of 1? The influence of the aryl substituents of the five-membered ring on the position of the stretching vibration of the cumulene bond and the 13C-NMR spectrum indicate that 1′ has some, but not all too great, importance. The derivatives of 1, which were obtained in acceptable yields, moreover, show very seldomly observed emission from an S2 state.
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Toda et al. (1987) studied this question.
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