Structural Characterization of Mixed-Stack Charge Transfer Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane and 5,10-Dimethyl-5,10-dihydrophenazine Prepared by the Langmuir−Blodgett Technique and Donor Doping. 1. Molecular Orientation and Structure Investigated by Ultraviolet−Visible−Near-Infrared and Infrared Spectroscopies and X-ray Diffraction

Abstract

Molecular orientation and structure in mixed-stack charge transfer (CT) films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) doped by 5,10-dimethyl-5,10-dihydrophenazine ((Me)2P) have been investigated by using ultraviolet−visible−near-infrared (UV−vis−NIR) and infrared (IR) spectroscopies and X-ray diffraction. The degree of charge transfer (ρ) was determined to be 0.5 by a shift of a b1u C⋮N stretching band of the TCNQ chromophore, suggesting that the complex is close to the neutral−ionic boundary. An X-ray diffraction pattern indicates that the CT films consist of a highly ordered multilayered structure in which donor ((Me)2P) and acceptor (octadecyl-TCNQ) molecules are periodically arranged. The d value was calculated to be 3.3 nm, implying that each layer of the CT films comprises bimolecular layers. Comparison of IR intensities of b1u, b2u, and ag C⋮N stretching bands of the acceptor (A) and a totally symmetric band at 1255 cm-1 of the donor (D) between the transmission and reflectance absorption (RA) IR spectra indicates that the chromophores of D and A are almost perpendicular to the substrate surface with their long molecular axes being nearly parallel to the surface normal in the one-layer mixed-stack CT films. The hydrocarbon chain of octadecyl-TCNQ was evaluated to lie on the substrate. In the multilayer CT films the D and A chromophoric planes seem to be slightly tilted with respect to the substrate surface.

Structural Characterization of Mixed-Stack Charge Transfer Films of 2-Octadecyl-7,7,8,8-tetracyanoquinodimethane and 5,10-Dimethyl-5,10-dihydrophenazine Prepared by the Langmuir−Blodgett Technique and Donor Doping. 3. Thickness Dependence of Thermal Behavior Investigated by Ultraviolet−Visible−Near-Infrared and Infrared Spectroscopies and X-ray Diffraction

“…The measurements were carried out over a temperature range from room temperature to 90 °C at an increment of 10 °C. Peaks at 2θ = 2.7°, 8.0°, and 10.7° are assigned to the first-, third-, and fourth-order diffractions in the CT film at room temperature . The diffraction pattern illustrates that a well-oriented arrangement of D (donor) and A (acceptor) molecules exists in the highly ordered multilayered structure, which consists of the bimolecular layers.…”

“…Sample Preparation. The procedure for the preparation of the mixed-stack CT films of octadecyl-TCNQ and (Me) 2 P was described in detail in the preceding paper . In the experiments presented in this paper, the 1-, 3-, 7-, and 11-layer CT films were prepared on CaF 2 substrates by (Me) 2 P doping of LB films of octadecyl-TCNQ in the vapor phase for 6, 12, 20, and 24 h, respectively, to ensure complete formation of the CT complexes.…”

“…Spectroscopy and X-ray Diffraction . The instruments employed for the UV−vis−NIR and IR spectroscopic measurements and X-ray diffraction experiments were the same as those described in the first paper . The apparatus and sample-handling technique for measuring the UV−vis−NIR and IR spectra and X-ray diffraction patterns at elevated temperatures were reported previously …”

“…In the preceding papers, − the structure, molecular orientation, morphology, and annealing effects have been reported for the mixed-stack charge transfer (CT) complex films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) doped by 5,10-dimethyl-5,10-dihydrophenazine ((Me) 2 P). The present paper, as a successive report, discusses the thermal behavior of the mixed-stack CT films investigated by X-ray diffraction and ultraviolet−visible−near-infrared (UV−vis−NIR) and infrared (IR) spectroscopies.…”

Substitution controlled molecular orientation and nanostructure in the Langmuir–Blodgett films of a series of amphiphilic naphthylidene-containing Schiff base derivatives

“…In present case, the vibration position suggested the alkyl chain kept basically in an ordered arrangement. We can further get the information on the orientation of the alkyl chain by comparison of the transmission and RAS spectra of the films [36][37][38][39]. In the transmission mode, the intensity of vibration at 2850 cm −1 is very near to that of the band at 2919 cm −1 .…”