MOLECULAR-ORIENTATION AND STRUCTURE IN EVAPORATED-FILMS OF 2-DODECYL-7,7,8,8-TETRACYANOQUINODIMETHANE, 2-PENTADECYL-7,7,8,8-TETRACYANOQUINODIMETHANE, AND 2-OCTADECYL-7,7,8,8-TETRACYANOQUINODIMETHANE STUDIED BY INFRARED AND RAMAN-SPECTROSCOPY

Infrared and Raman spectra have been measured for evaporated films of 2-dodecyl-7,7,8,8-tetracy-anoquinodimethane (dodecyl-TCNQ), 2-pentadecyl-7,7,8,8-tetracyanoquinodimethane (pentadecyl-TCNQ), and 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (octadecyl-TCNQ) deposited onto Au- or Ag-evaporated glass slides or CaF2 plates, and the obtained spectra have been compared with those of their Langmuir-Blodgett (LB) films previously. The relative intensities of infrared bands in the reflection-absorption (RA) spectrum indicate that the molecular orientation in the evaporated film of dodecyl-TCNQ on the Au- or Ag-evaporated glass slide is very close to that in its LB film; the hydrocarbon chain is tilted largely with its molecular plane nearly parallel to the surface and the TCNQ plane is nearly perpendicular to the surface in both films. The molecular orientation in the evaporated film of pentadecyl-TCNQ on the Au-or Ag-evaporated glass slide is also similar to that in its LB film. However, the molecular orientation in the evaporated film of octadecyl-TCNQ on the Au- or Ag-evaporated glass slide is markedly different from that in its LB film; the alkyl chain of octadecyl-TCNQ is tilted largely with its molecular plane nearly perpendicular to the surface and the TCNQ plane is inclined largely in the evaporated film. The molecular orientation in the evaporated films of octadecyl-TCNQ shows clear substrate dependency; the alkyl chain in the films on the CaF2 Plate is not so largely tilted as that on the Au- or Ag-evaporated glass slide. The infrared and Raman frequencies of the bands arising from the TCNQ chromophore do not change between the spectra of the evaporated films and those of the solid states for the three alkyl-TCNQ compounds. These observations lead us to conclude that the interaction between the TCNQ part and Au or Ag surface is very weak.