光谱学与光谱分析, 2010, 30 (4): 892, 网络出版: 2011-01-26
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
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
红外光谱 CH2剪式振动 晶体场分裂 2-烷基TCNQ Infrared spectra CH2 scissoring band Crystal field splitting 2-alkyl-TCNQ
摘要
测量了2-烷基TCNQ(C8TCNQ, C12TCNQ, C18TCNQ)浇铸膜的红外光谱, 发现这类化合物的红外CH2剪式振动在1 471和1 462 cm-1处显示2个峰。 这2个峰的强度比(I1 471/I1 462)随着烷基链的长度增加而明显减少。 另外, 来自CH2的1 471 cm-1吸收峰与来自TCNQ环的1 529 cm-1吸收峰的相对强度随着碳链的长度增加而不发生变化。 CnTCNQ系列化合物的红外光谱CH2的剪式振动行为与长链脂肪酸中CH2行为很不相同。 在长链脂肪酸中, 晶体场效应导致了剪式振动分裂。 考虑C12TCNQ的晶体结构, 而将1 471 cm-1峰归属为非叉指对接的碳链, 将1 462 cm-1峰归于叉指对接的碳链, 双峰的出现与晶体场分裂无关。 并且得到烷基TCNQ中, 非叉指对接的碳链的长度与碳链总长度无关的结论。
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.
王海水, 杨燕花, 尾崎幸洋. 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(4): 892. WANG Hai-shui, YANG Yan-hua, OZAKI Yukihiro. 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[J]. Spectroscopy and Spectral Analysis, 2010, 30(4): 892.