Preparation and Structural Characterization of Mixed-Stack Charge-Transfer Langmuir−Blodgett Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane and N,N,N‘,N‘-Tetramethylbenzidine

Abstract

One-, three-, and seven-layer Langmuir-Blodgett (LB) films of a mixed-stack charge-transfer (CT) complex of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (C18TCNQ) and N,N,N′,N′-tetramethylbenzidine (N-TMB) were successfully deposited onto CaF2 plates and gold-evaporated glass slides at the surface pressure of 10 mN m -1 . This is the first time that the mixed-stack CT films of N-TMB‚C18TCNQ have been prepared by the LB technique. Ultraviolet-visible-near-infrared (UV-vis-NIR) and infrared spectroscopies have been employed to investigate the formation, degree of charge transfer, molecular orientation, and structure of the CT complex in the LB films. The appearance of a broad absorption band with its center at about 1750 nm reveals that the CT complex in the LB films is in the mixed-stack form. The frequency of a CtN stretching band of C18TCNQ in the CT complex indicates that the degree of charge transfer (F) is about 0.24. A comparison of the infrared band intensities between the transmission and RA spectra suggests that the chromophore planes for both C18TCNQ and N-TMB are nearly parallel to the substrate surface in the CT LB films. This result is in a good agreement with the requirement for the formation of the mixed-stack complex in which the donor and acceptor components should be in a face-to-face contact with each other. The hydrocarbon chain of C18TCNQ is considerably tilted with respect to the substrate normal in the CT LB films. The CT film (LB-doping film) of N-TMB‚C18TCNQ was also prepared by LBand donor-doping techniques. It was found that N-TMB‚C18TCNQ molecules are partly dissolved in the petroleum ether solution during the doping procedure.

Fabrication of TTF−TCNQ Charge-Transfer Complex Self-Assembled Monolayers: Comparison between the Coadsorption Method and the Layer-by-Layer Adsorption Method

“…FTIR−RAS experiments were carried out to examine charge transfer in TTF−CH 2 SH/TCNQ SAMs on Au (111). , In the IR spectra, we have paid attention to the CN stretching band of the TCNQ molecule because this band is the most efficient probe to confirm the formation of CT complexes in the films. In general, the CN stretching band appears at 2228 cm -1 in the IR spectrum of neutral TCNQ, whereas it exhibits a low-frequency shift by 5−45 cm -1 in proportion to the degree of charge transfer δ in the spectra of the CT complexes containing TCNQ δ- . It is also convenient that no other vibrational modes in TTF−CH 2 SH/TCNQ SAMs are overlapped in this frequency region.…”

“…In general, the CN stretching band appears at 2228 cm -1 in the IR spectrum of neutral TCNQ, whereas it exhibits a low-frequency shift by 5-45 cm -1 in proportion to the degree of charge transfer δ in the spectra of the CT complexes containing TCNQ δ-. 49 It is also convenient that no other vibrational modes in TTF-CH 2 SH/ TCNQ SAMs are overlapped in this frequency region.…”

Thin Films of Molecular Metals TTF-TCNQ

“…The recent discovery of ambipolarity, coherent light emission and superconductivity in neutral molecular organic materials upon charge injection (3) has increased the effort in the preparation of highly pure, crystalline and oriented thin films. Such films can be obtained by organic chemical vapor deposition (OCVD) (4), thermal sublimation in vacuum (5), organic vaporphase deposition (OVPD) (6), organic molecular beam deposition (OMBD) (7), co-evaporation (8), the Langmuir-Blodgett technique (9) and electrochemical crystallization (10). Recently, the preparation of thin single crystals by confined electrocrystallization has been reported (11).…”

Electrochemical Quartz Crystal Microbalance Studies on the Codeposition of Dextran Sodium Sulfate with the Charge‐Transfer Complexes Generated During Electrooxidation of Benzidine Derivatives

“…The blue intermediate has been identified as a charge transfer complex (CTC), a partially oxidized dimeric semiquinone imine that is structurally similar to quinhydrone [3,4]. The electrooxidation of TMB was reported to be very similar to that of o-TD [7 -9], and TMB was also used as an electron donor (ED) for CTC investigations [10,11]. o-DA was used as a chromogen for characterization of peroxidase activity [12 -14], and for determination of free chlorine [15,16], and the electrooxidation of which in H 2 SO 4 medium was found to follow a two-step EE mechanism [17,18].…”