Langmuir–Blodgett Films of Charge-Transfer Complexes: Ethylenedithio-Substituted Amphiphilic Bis-TTF Macrocycle and F4TCNQ or Br2TCNQ

Abstract

Abstract Charge-transfer (CT) complexes between ethylenedithio-substituted bis-TTF macrocycle 1a, as an amphiphilic electron donor, and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) derivatives, as electron acceptors, were fabricated as Langmuir–Blodgett (LB) films. For the 1a–F4TCNQ LB film deposited at a surface pressure of 5 mN m−1 onto a substrate surface, the stoichiometry between the donor and acceptor was determined as 1:2 using XPS measurements. In contrast, a donor/acceptor ratio of 1:0.3 was observed for the 1a–Br2TCNQ LB film, indicating that a fraction of Br2TCNQ was lost during the LB film formation process. Similarity of the round-shaped domains that cover the surfaces of the 1a–Br2TCNQ and neutral 1a LB films indicates the presence of neutral 1a within the 1a–Br2TCNQ LB film. For the (1a2+)(F4TCNQ−)2 LB film, the presence of a CN-stretching frequency signifies the formation of a fully ionic electronic ground state. The LB film of 1a–Br2TCNQ exhibited a broad absorption at ca. 3 × 103 cm−1, which is characteristic of an intermolecular CT transition for a partial CT state. 1a–Br2TCNQ LB film consisted of neutral 1a and CT complex of 1a–Br2TCNQ. The room temperature conductivity of the 1a–Br2TCNQ LB film (1.2 × 10−2 S cm−1) was two orders of magnitude higher than that of 1a–F4TCNQ (3.9 × 10−4 S cm−1).