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 b earing electron-withdrawing groups in dimethyl-formamide at room temperatur e has revealed that symmetric compounds form intramolecular dimer radical a nions as an intermediate of their reductive C-O bond dissociation giving di arylmethyl radicals. The dimer radical. anions showed an absorption band in the near infrared region (NIR) (1000-1600 nm) characteristic to their char ge resonance (CR) properties. On the contrary to 1, 1-diarylmethanols, corr esponding radical anion of 1,3-diarylpropan-1-ol showed no CR band. It is s uggested that formation of dimer radical anions is energetically favorable for diaryl compounds with one-atom spacer but unfavorable for them with thr ee-atom spacer being different From the n = 3 rule for the favorable format ion of intramolecular excimers. (C) 2000 Elsevier Science B.V. All rights r eserved.