Kocsis Laura S, Elbel Kristyna M, Hardigree Billie A, Brummond Kay M, Haidekker Mark A, Theodorakis Emmanuel A
Department of Chemistry, University of Pittsburgh, 219 Parkman Avenue, Pittsburgh, PA 15260, USA.
Org Biomol Chem. 2015 Mar 14;13(10):2965-73. doi: 10.1039/c4ob02563f.
We describe the design, synthesis and fluorescent profile of a family of environment-sensitive dyes in which a dimethylamino (donor) group is conjugated to a cyanoacrylate (acceptor) unit via a cyclopenta[b]naphthalene ring system. This assembly satisfies the typical D-π-A motif of a fluorescent molecular rotor and exhibits solvatochromic and viscosity-sensitive fluorescence emission. The central naphthalene ring system of these dyes was synthesized via a novel intramolecular dehydrogenative dehydro-Diels-Alder (IDDDA) reaction that permits incorporation of the donor and acceptor groups in variable positions around the aromatic core. A bathochromic shift of excitation and emission peaks was observed with increasing solvent polarity but the dyes exhibited a complex emission pattern with a second red emission band when dissolved in nonpolar solvents. Consistent with other known molecular rotors, the emission intensity increased with increasing viscosity. Interestingly, closer spatial proximity between the donor and the acceptor groups led to decreased viscosity sensitivity combined with an increased quantum yield. This observation indicates that structural hindrance of intramolecular rotation dominates when the donor and acceptor groups are in close proximity. The examined compounds give insight into how excited state intramolecular rotation can be influenced by both the solvent and the chemical structure.
我们描述了一类对环境敏感的染料的设计、合成及荧光特性，其中二甲基氨基（供体）基团通过环戊并[b]萘环系统与氰基丙烯酸酯（受体）单元共轭。这种组装满足了荧光分子转子的典型D-π-A结构，表现出溶剂化显色和对粘度敏感的荧光发射。这些染料的中心萘环系统是通过一种新型的分子内脱氢脱氢狄尔斯-阿尔德（IDDDA）反应合成的，该反应允许在芳环核心周围的可变位置引入供体和受体基团。随着溶剂极性的增加，观察到激发峰和发射峰发生红移，但当染料溶解在非极性溶剂中时，呈现出具有第二个红色发射带的复杂发射模式。与其他已知的分子转子一致，发射强度随粘度增加而增加。有趣的是，供体和受体基团之间更近的空间距离导致粘度敏感性降低，同时量子产率增加。这一观察结果表明，当供体和受体基团靠近时，分子内旋转的结构阻碍起主导作用。所研究的化合物有助于深入了解激发态分子内旋转如何受到溶剂和化学结构的影响。
