title: Synthesis and optical and electrochemical properties of julolidine-structured pyrido[3,4-b]indole dye.
abstract: 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,1H 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.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. yooyama@hiroshima-u.ac.jp.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Enoki
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. yooyama@hiroshima-u.ac.jp.
authors.forename: Keishi
authors.initials: K
authors.lastname: Matsuo
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. yooyama@hiroshima-u.ac.jp.
authors.forename: Joji
authors.initials: J
authors.lastname: Ohshita
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan. yooyama@hiroshima-u.ac.jp.
authors.forename: Yousuke
authors.identifier: http://orcid.org/0000-0002-0257-6930
authors.initials: Y
authors.lastname: Ooyama