Germylenes singlet excited state

Recently, CIDNP effects have also been observed in the reactions of carbenes containing silicon and germanium with various scavengers. In this case, the radical stages have been detected in the reaction of singlet (ground) and triplet (excited) states of dimethylsilylene and -germylene. 

Thus, the sign of the observed polarization of the Me protons of the product 22 (absorption) is unambiguous evidence of the formation of an intermediate triplet 1,3-biradical 23T, and this fact, in turn, means that 16 enters the reaction with 21 in the excited triplet state. The end product 22 is formed after the triplet-singlet conversion of the triplet biradical 23t followed by cyclization of the singlet biradical 23s (Scheme 11), while the triplet biradical 23T also reverts to the initial reagents. Only this reverse reaction could explain the negative polarization (emission) of the Me protons of the initial thiacycloheptyne 21. It should be noted that the process described in Scheme 11 is the first example of a reaction of the excited triple state of germylene 1676. 

---