Charge-transfer complexations of 1,n-di(9-ethylcarbazol-3-yl) alkanes with tetracyanoethylene and tetranitromethane

1,n-Di(9-ethylcarbazol-3-yl)alkanes, where n = 1-5, as the dichromophoric model compounds of poly-3-vinylcarbazoles were synthesized to examine their complexation behaviors with the electron acceptors tetracyanoethylene (TCNE) and tetranitromethane (TNM). 9,9'-Diethyl-3,3'-dicarbazolyl, di(3-ethyl carbazol-9-yl)methane, and three monomeric analogues were also included for comparison. In dichloromethane solution, the dicarbazoles formed stable 1:1 electron donor-acceptor complexes with TCNE having formation enthalpies around -3.5 kcal/mol. With TNM they formed more weakly bound complexes that showed little dependence on concentration and almost zero dependence on temperature changes having nearly 0 kcal/mol enthalpies of formation. The smaller gap between the two carbazole groups in 1,n-di(9-ethylcarbazol-3-yl)alkanes with n <= 2 affected complexation adversely, while such an effect was not observed in the dicarbazoles with n >= 3. (C) 2008 Elsevier B.V. All rights reserved.