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
WANG Hai-shui1, YANG Yan-hua1, OZAKI Yukihiro2
1. School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou 510640, China 2. Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan
Abstract：Infrared (IR) spectra were measured for 2-octyl-, 2-dodecyl-, and 2-octadecyl-7,7,8,8-tetracyanoquinodimethane (C8TCNQ, C12TCNQ and C18TCNQ) 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 (CC stretching mode of the TCNQ chromophore ring) does not change significantly for the three kinds of CnTCNQ 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 CnTCNQ 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 C12TCNQ 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 CnTCNQ 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 CnTCNQ could also be reached.
Key words：Infrared spectra;CH2 scissoring band;Crystal field splitting;2-alkyl-TCNQ
王海水1，杨燕花1，尾崎幸洋2 . 2-烷基TCNQ的红外光谱和结构研究——CH2剪式振动的双峰与晶体场分裂的关系[J]. 光谱学与光谱分析, 2010, 30(04): 892-896.
WANG Hai-shui1, YANG Yan-hua1, OZAKI Yukihiro2 . 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 . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2010, 30(04): 892-896.
[1] Snyder R G. J. Mol. Spectrosc. 1961, 7: 116. [2] Holland R F, Nielsen J R. J. Mol. Spectrosc., 1962, 8(5): 383. [3] Holland R F, Nielsen J R. J. Mol. Spectrosc., 1962, 9(6): 436. [4] WANG Yi-bing, WU Wei-hong, LU Fei, et al(王一兵, 吴卫红, 芦 菲, 等). Spectroscopy and Spectral Analysis(光谱学与光谱分析), 2008, 28(5): 1140. [5] Kimura F, Umemura J, Takenaka T. Langmuir, 1986, 2: 96. [6] Ren Y, Iimura K, Kato T. J. Chem. Phys., 2001, 114: 1949. [7] Ren Y, Hossain M M, Iimura K, et al. J. Phys. Chem. B, 2001, 105: 7723. [8] Terashita S, Suzuki T, Nakatsu K, et al. Bull. Chem. Soc. Jpn., 2001, 74: 2019. [9] Wang Y, Nichogi K, Terashita S, et al. J. Phys. Chem., 1996, 100: 368. [10] Wang Y, Nichogi K, Iriyama K, et al. J. Phys. Chem. 1996, 100: 374. [11] Nichogi K, Murakami M. Thin Solid Films, 1998, 325: 204. [12] Terashita S, Nakatsu K, Ozaki Y, et al. Langmuir, 1992, 8: 3051. [13] Terashita S, Ozaki Y, Iriyama K. J. Phys. Chem., 1993, 97: 10445. [14] Nakagoshi A, Terashita S, Ozaki Y, et al. Langmuir, 1994, 10: 779. [15] Wang H, Ozaki Y. Appl. Spectrosc., 2000, 54: 692. [16] Morita S, Nichogi K, Ozaki Y. J. Phys. Chem. B, 2004, 108: 7871.
