Synthesis and optical properties, including fluorosolvatochromic and ICT-based proton-sensing behaviors of a series of 2,4,6-tris(5-aryl-2-thienyl)pyridines

Abstract

A series of 2,4,6-tris(5-aryl-2-thienyl)pyridines with a star-shaped π–conjugated (D-π)₃-A system, which consist of an electron deficient pyridine core (A) and three aryl groups with an electron-donating substituent (D) linked by a thiophene spacer (π-spacer), were designed and systematically synthesized. The optical properties of these molecules in the solution and solid states, which were identified by UV-vis absorption and fluorescence spectroscopies, clearly indicated that the UV-vis absorption and fluorescence wavelengths are controlled by the donor strength of the terminal aryl groups. Additionally, 2,4,6-tris[5-(4-N,N-dibutylaminophenyl)-2-thienyl]pyridine exhibited a fluorosolvatochromic behavior based on its strong intramolecular charge transfer (ICT) characteristic and displayed proton-induced two-step optical spectral shifts depending on its stepwise protonation of the amino nitrogen atoms and pyridinyl nitrogen atom with stepwise visual solution and fluorescence color changes. Consequently, we revealed that the molecule serves as an optical sensor capable of the visual detection of solvent polarity and a proton.

Graphical Abstract

Keywords:

• Star-shaped molecule
• pyridine
• intramolecular charge transfer
• fluorosolvatochromism
• proton-sensing

Additional information

Funding

This study was supported by JSPS KAKENHI Grant Number JP16K20897.