Chao Chun-Chieh, Leung Man-kit, Su Yuhlong Oliver, Chiu Kuo-Yuan, Lin Tsung-Hsien, Shieh Shwu-Ju, Lin Shien-Chang
Department of Chemistry and Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan 106, ROC.
J Org Chem. 2005 May 27;70(11):4323-31. doi: 10.1021/jo050001f.
Substituent effects on the photophysical and electrochemical properties of 1,7-diaryl-substituted perylene diimides (1,7-Ar(2)PDIs) have been carefully explored. Progressive red-shifts of the absorption and emission maxima were observed when the electron-donating ability of these substituents was increased. Linear Hammett correlations of 1/lambda(max) versus sigma(+) were observed in both spectral analyses. The positive slopes of the Hammett plots suggested that the electronic transitions carry certain amounts of photoinduced intramolecular charge-transfer (PICT) character from the aryl substituents to the perylene diimide core which leads to the reduction of the electron density on the substituents. The substituent electronic effects originated mainly from the perturbation of the core PDI HOMO energy level by the substituents. This conclusion was supported by PM3 analyses and confirmed by cyclic voltammetry experiments. More interestingly, the Ph(2)NC(6)H(4)-substituted PDI, 4i, showed an unusual dual-band absorption that spans from 450 to 750 nm. We tentatively assigned these two bands as the charge-transfer band and the PDI core absorption, respectively.
已对取代基对1,7 - 二芳基取代苝二酰亚胺（1,7 - Ar(2)PDIs）光物理和电化学性质的影响进行了仔细研究。当这些取代基的给电子能力增强时，观察到吸收和发射最大值出现渐进红移。在两种光谱分析中均观察到1/λ(max)与σ(+)的线性哈米特相关性。哈米特图的正斜率表明，电子跃迁具有一定量的从芳基取代基到苝二酰亚胺核心的光致分子内电荷转移（PICT）特征，这导致取代基上电子密度降低。取代基电子效应主要源于取代基对核心PDI HOMO能级的扰动。这一结论得到了PM3分析的支持，并通过循环伏安实验得到证实。更有趣的是，Ph(2)NC(6)H(4)取代的PDI，即4i，显示出跨越450至750 nm的异常双波段吸收。我们初步将这两个波段分别归为电荷转移带和PDI核心吸收带。
