Observation of intramolecular dimer radical anion of 1,1-diarylmethanols bearing electron withdrawing groups at room temperature

Transient absorption measurement of radical anions of 1,1-diarylmethanols bearing electron-withdrawing groups in dimethyl-formamide at room temperature has revealed that symmetric compounds form intramolecular dimer radical anions as an intermediate of their reductive C–O bond dissociation giving diarylmethyl radicals. The dimer radical anions showed an absorption band in the near infrared region (NIR) (1000–1600 nm) characteristic to their charge resonance (CR) properties. On the contrary to 1,1-diarylmethanols, corresponding radical anion of 1,3-diarylpropan-1-ol showed no CR band. It is suggested that formation of dimer radical anions is energetically favorable for diaryl compounds with one-atom spacer but unfavorable for them with three-atom spacer being different from the n=3 rule for the favorable formation of intramolecular excimers.