Two types of diphenyldiazomethanes having two trifluoromethyl and two bromine groups at the ortho positions, either in unsymmetrical or in symmetrical fashion, that is, (2,6-dibromo-4-phenylphenyl)[4-phenyl-2,6-bis(trifluoromethyl)phenyl]diazomethane (U-1-N2) and bis(2-bromo-4-phenyl-6-trifluoromethylphenyl)diazomethane (S-1-N2), are prepared. Triplet diphenylcarbenes (U-(3)1 or S-(3)1) are generated