Charge-Transfer Complexes between Indoline-Tricyanoquinodimethane Compounds and 7,7,8,8-Tetracyanoquinodimethane

intramolecular charge-transfer compounds composed of 1-alkyl-3,3-dimethyl-2-methyleneindoline (I-n, donor, n = alkyl chain length; 1 or 6) and 7,8,8-tricyanoquinodimethane (=2-(4'-cyanomethylene-2',5'-cyclohexadienylidene)-malononitrile, 3CNQ, acceptor) moieties afforded charge-transfer complexes with 7,7,8,8-tetracyanoquinodimethane (TCNQ): (I-1-3CNQ)(2)(TCNQ) and (I-6-3CNQ)(TCNQ). (I-1-3CNQ)(2)(TCNQ) included two kinds of I-1-3CNQ molecules of different molecular conformations. (I-1-3CNQ)(2)(TCNQ) and (I-6-3CNQ)(TCNQ) were constructed from one-dimensional columns of 3CNQ center dot center dot center dot TCNQ center dot center dot center dot 3CNQ triads and 3CNQ center dot center dot center dot TCNQ dyads, respectively. These complexes exhibited intermolecular charge-transfer bands extending to the near IR region (1000-1500 nm) in addition to intramolecular charge-transfer bands around 600-900 nm characteristic of I-n-3CNQ compounds. They were characterized as weak charge-transfer solids from estimations of' the degree of charge transfer using molecular orbital calculations, bond lengths, and vibration spectra. Intermolecular charge transfer caused a slight increase in the degree of intramolecular charge transfer.