Langmuir−Blodgett Films of Charge-Transfer Complexes between an Amphiphilic Monopyrrolo-TTF and TCNQ Derivatives

Abstract

Electrically active Langmuir−Blodgett (LB) films based on charge-transfer (CT) complexes between an amphiphilic monopyrrolo-tetrathiafulvalene (MP-TTF) electron donor and different derivatives of the electron acceptor 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), namely, 2,5-difluoro-TCNQ, fluoro-TCNQ, TCNQ, decyl-TCNQ, 2,5-dimethyl-TCNQ, and 2-methoxy-5-ethoxy-TCNQ, have been fabricated and investigated systematically. The electronic ground state of the CT complex, (MP-TTF+δ)(TCNQs-δ), in the LB films varied from ionic (δ = 1) to neutral (δ ∼ 0) depending on the electron affinity of the TCNQ derivative used. CT excitation energies of the LB films were correlated against the difference between the redox potentials of the MP-TTF and TCNQ derivatives, exhibiting agreement with a neutral−ionic (N−I) phase diagram proposed for mixed-stack CT complexes. Of the six kinds of LB films, the (MP-TTF+0.3)(decyl-TCNQ-0.3) and (MP-TTF+0.6)(TCNQ-0.6) complexes were located closest to the N−I phase boundary. In all of the...