Enoki Toshiaki, Matsuo Keishi, Ohshita Joji, Ooyama Yousuke
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan.
Phys Chem Chem Phys. 2017 Feb 1;19(5):3565-3574. doi: 10.1039/c6cp08573c.
The julolidine-structured pyrido[3,4-b]indole dye ET-1 has been newly designed and developed as a small D-A fluorescent dye. ET-1 showed bathochromic shifts of the fluorescence band upon changing from aprotic solvents to protic solvents, as well as positive fluorescence solvatochromism. Moreover, it was found that ET-1 can form a 1 : 1 Py(N)-B complex with boron trifluoride and a hydrogen-bonded proton transfer (Py(N)-H) complex with trifluoroacetic acid, which exhibit photoabsorption and fluorescence bands at a longer wavelength region than the pristine ET-1. Based on optical (photoabsorption and fluorescence spectroscopy) and electrochemical (cyclic voltammetry) measurements, Lippert-Mataga plots, H NMR spectral measurement and density functional theory (DFT) calculation, this work indicated that the Py(N)-B complex or the Py(N)-H complex is effectively formed and stable in solution. This is due to the strong Py(N)-B interaction or Py(N)-hydrogen-bond, which can be attributed to the enhanced basicity or the accumulated electron density on the nitrogen atom of the pyridine ring caused by the introduction of a julolidine (quinolizidine) moiety as a strong electron-donating group. We propose that the D-A-type dye ET-1 based on the julolidine-structured pyrido[3,4-b]indole possesses the ability to act as a calorimetric and fluorescent sensor for Brønsted and Lewis acids.
具有久洛里定结构的吡啶并[3,4 - b]吲哚染料ET - 1作为一种小型给体 - 受体（D - A）荧光染料被新设计和开发出来。当从非质子溶剂变为质子溶剂时，ET - 1的荧光带出现红移，同时呈现正的荧光溶剂化显色现象。此外，发现ET - 1能与三氟化硼形成1∶1的吡啶氮 - 硼（Py(N)-B）配合物，与三氟乙酸形成氢键质子转移（Py(N)-H）配合物，这些配合物在比原始ET - 1更长的波长区域呈现光吸收和荧光带。基于光学（光吸收和荧光光谱）和电化学（循环伏安法）测量、Lippert - Mataga图、氢核磁共振光谱测量以及密度泛函理论（DFT）计算，这项工作表明Py(N)-B配合物或Py(N)-H配合物在溶液中能有效形成且稳定。这是由于强的Py(N)-B相互作用或Py(N)-氢键，这可归因于作为强供电子基团引入久洛里定（喹嗪）部分导致吡啶环氮原子上碱性增强或电子密度积累。我们提出基于久洛里定结构的吡啶并[3,4 - b]吲哚的D - A型染料ET - 1具有作为布朗斯特酸和路易斯酸的比色和荧光传感器的能力。
