(Tetrahydrodibenzo[<i>a</i>,<i>i</i>]phenanthridin-5-yl)phenol as a Fluorescent Probe for the Detection of Aniline

Abstract

Two (tetrahydrodibenzo[<i>a</i>,<i>i</i>]phenanthridin-5-yl)phenols that differ in their substituents at the para position (<b>P1</b>, R = H and <b>P2</b>, R = NEt₂) were designed and synthesized. The presence of a -NEt₂ group in probe <b>P2</b> facilitates the twisted intramolecular charge transfer (TICT) process, making <b>P2</b> emissive, which distinctly coordinated with boron trifluoride in the presence of different amines with different electronic properties. A substantial increase in emission intensity with increasing viscosity of the surrounding environment and smooth formation of a planar complex with boron and Zn²⁺ ions concluded the presence of a TICT process. The selective reactivity of <b>P2</b> toward a tetracoordinated boron complex has been explored as a potential tool for colorimetric and fluorescent discrimination of aromatic primary amines, i.e., anilines. Selective detection of aniline with probe <b>P2</b> can be viewed through the naked eye, and the corresponding fluorescence turn-on detection limit was found to be 12.65 nM. In addition, the detection of aniline on precoated aluminum-backed thin-layer chromatography plates and Whatman filter paper strips was found to be in good agreement with the color change of <b>P2</b> in solution and in vapor phase.