Infrared Band Assignments and Structure of Even-Numbered 2-Alkyl-7,7,8,8-Tetracyanoquinodimethane in Cast Films-Two Components of the CH2 Scissoring Vibrations not Related to Crystal Field Splitting
ABSTRACT Infrared (IR) spectra were measured for 2-octyl-, 2-dodecyl-, and 2-octadecyl-7, 7, 8, 8-tetracyanoquinodimethane (C8TCNQ, C12 TCNQ and C18 TCNQ) in cast films, and it was found that each spectrum shows two components for the CH2 scissoring band at 1 471 and 1 462 cm(-1). Polarized IR measurements showed that the micro-crystallites in the cast films take a random orientation in the plane of the plate. The intensity ratio of the two bands at 1 471 and 1 462 cm(-1) (I1 471/I1 462) decreases observably with the increase in the length of the alkyl chain. Moreover, the relative intensity of the 1 471 cm(-1) CH2 band to a band at 1 529 cm(-1) (C=C stretching mode of the TCNQ chromophore ring) does not change significantly for the three kinds of C(n) TCNQ while the relative intensity of the 1 462 cm(-1) CH2 band to the band at 1 529 cm(-1) increases markedly with the length of the alkyl chain. The above variations of the CH2 scissoring doublet of C(n) TCNQ are quite different from those of long-chain fatty acids (stearic acid and lignoceric acid) where the splitting of the CH2 scissoring vibration occurs due to a crystal field splitting. Considering the crystal structure of C12 TCNQ and the above spectral variations, the authors assign the two components of the CH2 scissoring bands at 1 462 and 1 471 cm(-1) of the C(n) TCNQ cast films to the interdigitated and non-interdigitated parts of the alkyl chains, respectively. Furthermore, the conclusion that the length of the non-interdigitated part of the alkyl chain is almost unchanged in the three kinds of even-numbered C(n) TCNQ could also be reached.
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ABSTRACT: The annealing effects on Langmuir−Blodgett (LB) films of 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (abbreviated as octadecyl-TCNQ) have been investigated by atomic force microscopy (AFM) and ultraviolet−visible (UV−vis) and infrared (IR) spectroscopies. An AFM image of a one-layer LB film of octadecyl-TCNQ scanned at room temperature shows that the film consists of numerous platelike microcrystal domains. A periodic structure of octadecyl-TCNQ molecules with a period of 0.85 nm can be observed inside these domains. After the annealing, cooling down the film from 130 to 30 °C, some of these domains lie on top of one another, keeping their original morphology. The rest seem to melt into a globular bulk sample. In the case of an 11-layer film, it can be seen from its AFM images that a number of domains with smaller size cover the substrate and that they completely melt after the annealing cycle. The UV−vis spectra of the one- and 11-layer films measured before and after the annealing show that the stacked structure of the TCNQ chromophore recovers partially for the one-layer film, but it recovers little for the 11-layer film. The IR measurements of the one-, three-, seven-, and 11-layer LB films before and after the annealing reveal that the subcell packing of the hydrocarbon chain changes due to the cyclic temperature treatment up to 130 °C. The present study also demonstrates that the annealing effects on the LB films of octadecyl-TCNQ are largely different from those on LB films of simple amphiphilic compounds such as fatty acids.The Journal of Physical Chemistry 01/1996; 100(1). DOI:10.1021/jp952164l · 2.78 Impact Factor
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ABSTRACT: The infrared spectra of four different crystal forms of octadecanoic acid were investigated with the aid of a Perkin-Elmer Model 112 double-pass spectrometer equipped with polarizer and reflecting microscope. For the triclinic A-form spectra of a single crystal were observed with the electric field in the linearly polarized incident radiation parallel and perpendicular to the skeletal planes of the methylene chains. For the monoclinic B- and C-forms spectra were obtained of single crystals, and of suitably cut slices of single crystals, with the electric field parallel to the a-axis, the b-axis, the c-axis, and perpendicular to the c-axis. A new, evidently monoclinic, crystal form was discovered, and spectra of a single crystal of this form were obtained with the electric vector parallel to the a- and b-axes. Deuterated octadecanoic acid, CH3(CH2)16COOD, was prepared, and spectra were obtained of single crystals having the C-form and the new form. The spectral data were used to verify, extend or revise previous interpretations of the infrared bands of octadecanoic acid.Journal of Molecular Spectroscopy 01/1962; DOI:10.1016/0022-2852(62)90250-3 · 1.53 Impact Factor
- Langmuir 2(1). DOI:10.1021/la00067a017 · 4.38 Impact Factor