Photoionization of dimethylaniline and of the donor–aromatic-acceptor molecules p-(CH3)2NC6H4R, R = CN, COOH, COOEt, CHO, NO2, in glasses of ethanol and ethanediol/water at 77–125 K

Abstract

The u.v. photoionization of the donor–aromatic-acceptor molecules p-(CH₃)₂NC₆H₄R, R = CN (II), COOH (III), COOEt (IV), CHO (V), NO₂(VI), in glasses of ethanol or ethanediol/water (1/1 vol)(ED) at 77–125 K was investigated by u.v./vis. and e.s.r spectroscopy. With dimethylaniline (I) as a reference, visible absorption maxima from ED glasses at 570, 590, 590 and > 700 nm could be attributed to the radical cations (II^+˙)-(V^+˙), respectively. The corresponding extinction coefficients of (II^+˙)-(V^+˙) are 2.0 × 10³, 1.8 × 10³, 2.4 × 10³ and 2.7 × 10⁴ dm³ mol^–1 cm^–1 in ED at 125 K. E.s.r. spectra of u.v.-irradiated glasses of EtOH or ED containing either (I) or (II) showed the occurrence of the solvent radicals CH₃ĊHOH or · R₁OH, respectively. With increasing electron withdrawing ability of R the efficiency of the photoionization of p-(CH₃)₂NC₆H₄R seems to decrease.