Charge transfer states in stable neutral and oxidized radical adducts from carbazole derivatives.
In this paper we report the spectral properties of the stable radical adducts 1(•)-3(•), which are formed by an electron donor moiety, the carbazole ring, and an electron acceptor moiety, the polychlorotriphenylmethyl radical. The molecular structure of radical adduct 1(•) in the crystalline state shows a torsion angle of approximately 90° between the phenyl and the carbazole rings due to steric interactions. They exhibit a charge transfer band in the visible range of the electronic spectrum. All of them are chemically oxidized with copper(II) perchlorate to the respective cation species, which show a strong charge transfer band into the near-infrared region of the spectrum. Radical adducts 1(•)-3(•) and the corresponding stable oxidized species 1(+)-3(+) are real organic mixed-valence compounds due to the open-shell nature of their electronic structure. Charge transfer bands of the cation species are stronger and are bathochromically shifted with respect to those of the neutral species due to the greater acceptor ability of the positively charged central carbon atom of the triphenylmethyl moiety. The cationic species 1(+)-3(+) are diamagnetic, as shown by the absence of a signal in the EPR spectrum in acetonitrile solution at room temperature, but they show an intense and unique band in frozen solutions (183 K).
Departament de Quı́mica Biològica i Modelització Molecular, Institut de Quı́mica Avançada de Catalunya (CSIC) , Jordi Girona 18-26, 08034 Barcelona, Spain.
Lluís
L
Fajarí
Robert
R
Papoular
Marta
M
Reig
Enric
E
Brillas
José Luis
JL
Jorda
Oriol
O
Vallcorba
Jordi
J
Rius
Dolores
D
Velasco
Luis
L
Juliá