Effects of solvent polarity and structure on intersystem crossing in diphenylcarbenes. A picosecond laser study on dimesitylcarbene

The singlet to triplet intersystem crossing rate (kST) for a series of diphenylcarbene derivatives is found to be a sensitive function of the energy splitting (ΔEST), which in turn depends on the solvent polarity and on the structure of the carbene. A turn-over in the dependence of kST on ΔEST is found for the case of dimesitylcarbene (DMC), where kST is a decreasing function of ΔEST. The results for DMC provide the first example of intersystem crossing in the large gap limit for a carbene.