Charge Transfer Complexes of Thienyl‐Substituted Diazadiphosphapentalenes with 1,2,4,5‐Tetracyanobenzene: Synthesis, Structure, and Photoconductivity

3a, 6a-Diaza-1,4-diphosphapentalenes (RR'DDP) containing thienyl and alkyl peripheral substituents were synthesized (R, R' = {(5-ethylthienyl-2), Me} (6), {(thienyl-2), n-Bu} (7)). Interaction of 1,2,4,5-tetracyanobenzene (TCNB) with DDP 6 in any stoichiometry produces sandwich complex of the composition DDP-TCNB-DDP. Estimation of the HOMO-LUMO gap from the onset of optical absorption gives value of 1.34 eV. The study of the electron density topology showed that each TCNB molecule is an acceptor of 0.44e in the crystal while each DDP molecule in stack is charged + 0.22e. The energy of intermolecular interactions between the donor and acceptor molecules is 8.2 kcal/mol. We demonstrate for the first time the photoconductivity of a representative of a new class of charge-transfer complexes based on diazadiphosphapentalenes. Electrical measurements of single crystals of the (RR'DDP)/TCNB complex (R, R' = {(thienyl-2), Me} showed that the photocurrent under 1 Sun-irradiation is close to 1.5 nA, and the photosensitivity reaches 70. Complexation of TCNB with diazadiphosphapentalene 7 containing n-butyl peripheral substituents does not result in the formation of a stable complex. Analysis of ten representatives of diazadiphosphapentalenes showed that steric effects and the flexibility of peripheral substituents play a decisive role in complexation with TCNB.