五苯荑衍生之對苯丁二炔寡聚物之構形與光物理性質研究

Abstract

近年來化學家們對於苯乙炔共軛高分子和對苯丁二炔共軛高分子構形不同在光物理性質上造成的影響深感興趣。在本實驗室的研究中，觀測到五苯荑架構苯乙炔寡聚物，當降溫時，光譜研究顯示分子構形分布傾向於扭轉構形，此行為與一般苯乙炔寡聚物不同，為了了解在低溫下造成分子傾向扭轉構形的原因，是因為相鄰五苯荑間的立體效應或是電子效應所造成的，藉由丁二炔基來增長五苯荑間的距離，設計了化合物F-3和F-4。 我們成功的合成出五苯荑對苯丁二炔寡聚物F-3和F-4，利用變溫光物理性質的量測，更是首次看到對苯丁二炔寡聚物扭轉構形的放光。 我們發現溶劑環境的改變，也可能造成扭轉構形。當溫度下降時(300 K至180 K)，分子構形由平面構形平衡傾向扭轉構形，而當溶劑逐漸轉換成玻璃態時(160至80 K)，分子構形由扭轉構形平衡傾向平面構形。 我們藉由理論計算，變溫吸收光譜和晶體結構，證明化合物F-3扭轉構形相較於平面構形穩定，造成的原因是來自於相鄰五苯荑間的電子效應，不是立體效應。

Chemists are always interested in the relationship between conformation of -conjugated backbones and photophysical properties. In our previous work, when the temperature is lowered, the equilibrium of the conformers of pentiptycene-derived oligo(p-phenyleneethynylene)s shifts toward the twisted domains. The origin of the preference of a twisted conformation at low temperature is not fully understood. It is possible that the bulky iptycene substituents impose substantial interactions between the neighboring pentiptycene groups. Therefore, we designed compounds F-3 and F-4 where the pentiptycene groups are separated by butadiyne spacers. We have synthesized compounds F-3 and F-4 by using pentiptycene building blocks. These compounds are showing the emission of twisted conformers at lower temperature (180 K). Solvent effect has little influence on the geometries of the ground states of the planar and twisted forms. When the temperature is lowered (300-180K), the equilibrium of the conformers shifts toward the twisted domains. However, the equilibrium of the conformers shifts toward the planar domains in a glassy solvent (180-80K). According to theoretical calculation and experiment results of F-3, our experiments supported that the planar conformer was less stable than the twisted conformer. We found that the stabilization of the twisted conformer results from electronic effect rather than steric effect.