Graduate School of Life and Environmental Sciences, Kyoto Prefectural University , Shimogamo, Sakyo-ku, Kyoto 606-8522, Japan.
J Am Chem Soc. 2014 May 14;136(19):7101-9. doi: 10.1021/ja502209w. Epub 2014 May 1.
Using a bottom-up method, we prepared a series of oligonaphthofurans composed of alternating naphthalene rings and furan rings. The largest compound (compound 25) contained 8 naphthalene units and 7 furan units. DFT calculations revealed that these compounds were fan-shaped molecules and each naphthalene ring was oriented in an alternate mountain-valley fold conformation because of steric repulsion by the hydrogens at the peri-positions. We investigated the optical properties that derived from their fan-shaped and mountain-valley sequences. As the number of aromatic rings of the oligonaphthofurans increased, the peaks of the longest wavelength absorptions in the UV-vis spectra (HOMO-LUMO energy gap) of these compounds steadily red-shifted, although the shapes of spectra were not sustained because of the decreasing molar absorption coefficients (ε's) of their λ(max). We compared our results with those reported for other types of oligoaromatic compounds such as acenes 1, ethene-bridged p-phenylenes 2, rylenes 3, oligofurans 4, and oligonaphthalenes 5. The slopes of the plots between the transition energies (HOMO-LUMO energy gap) of the oligoaromatic compounds and the reciprocal of the number of aromatic rings indicated that the efficiency of π conjugation of the oligonaphthofurans was comparable with that of linear and rigid acenes and rylenes. The higher-order compounds 22 and 25 aggregated even under high dilution conditions (~10(-6) M).
我们采用自下而上的方法，合成了一系列由交替的萘环和呋喃环组成的寡聚萘并呋喃。最大的化合物（化合物 25）含有 8 个萘单元和 7 个呋喃单元。DFT 计算表明，这些化合物是扇形分子，由于邻位氢的空间位阻，每个萘环都呈现交替的山-谷折叠构象。我们研究了源于其扇形和山谷序列的光学性质。随着寡聚萘并呋喃中环数的增加，这些化合物在紫外-可见光谱（HOMO-LUMO 能隙）中最长波长吸收峰的位置（HOMO-LUMO 能隙）稳步红移，尽管由于摩尔吸光系数（ε's）的降低，光谱的形状没有保持不变λ（max）。我们将结果与其他类型的寡芳烃化合物如并苯 1、亚乙烯基桥联对苯 2、芴 3、寡呋喃 4 和寡萘 5 的报道结果进行了比较。寡芳烃化合物的跃迁能量（HOMO-LUMO 能隙）与芳香环数倒数之间的关系图的斜率表明，寡聚萘并呋喃的π 共轭效率与线性和刚性并苯和芴相当。较高阶的化合物 22 和 25 即使在高稀释条件下（~10(-6) M）也会聚集。
