Donor−Acceptor Complexes of Alkylcarbazole and Dicarbazolylalkane Donors with the Acceptors Tetracyanoethylene and Tetranitromethane

Electron donor−acceptor complexes of conformationally flexible 1, n -dicarbazolylalkanes (C 12 H 8 N−(CH 2 ) n −NC 12 H 8 ), where n = 1−5, were examined. Carbazole, methylcarbazole, ethylcarbazole, and cyanoethylcarbazole also were studied as monochromophoric analogues for comparison. In dichloromethane solution, the dicarbazolylalkanes form 1:1 complexes with the terminal carbazolyl chromophores acting as independent donors when n ≥ 2. With the acceptor tetranitromethane (TNM), the carbazoles form contact complexes displaying small positive enthalpies of formation. In contrast, stable complexes form with the acceptor tetracyanoethylene (TCNE). Crystalline TCNE complexes were isolated for the bichromophoric donors with n = 2−4. The solid complexes and their uncomplexed donor components were analyzed by single-crystal X-ray diffraction. The solid-state stoichiometries of (carbazolyl donor):(TCNE acceptor) were found to depend on the donor conformation. Dicarbazolylalkane donors separated by two or four methylene units exhibit a 1:1 donor:acceptor ratio and form stacked arrays of alternating donor and acceptor groups. A three-carbon bridging alkyl chain leads to local sandwich-type complexes in the solid state with a resulting donor:acceptor ratio of 4:1.