Langmuir-blodgett films of charge-transfer complexes: Ethylenedithio- substituted amphiphilicbis-ttf macrocycle and F₄TCNQ or Br ₂TCNQ

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 5mNm^-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 ratioof 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 filmof 1a-Br₂TCNQ exhibited a broad absorption at ca. 3 x 10³cm^-1, which is characteristicof 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 x 10 ^-2 S cm^-1) was two orders of magnitude higher than that of 1a-F₄TCNQ (3.9 x 10^-4Scm^-1).