Microwave-Assisted Synthesis of Triphenyl Amine-Based Phenyl Quinazolines: Investigation of Photophysical and Fluorescence Switching Behavior.

Abstract

Stimuli-responsive fluorescent materials with donor-acceptor systems hold significant potential for sensing applications. This study presents the synthesis, characterization, and photophysical properties of triphenylamine-cored mono (P1), triphenylamine-cored di (P2), and tri (P3) quinazolines using microwave-assisted methods. Probes exhibit fluorescence properties in solid state and solution, with positive solvatochromism observed as solvent polarity increased from toluene to DMSO. The presence of quinazoline acts as an electron-deficient group, while triphenylamine is an electron donor. The probes exhibited reversible switching behaviour in the solution state, indicating their sensitivity to volatile trifluoroacetic acid (TFA) and triethyl amine (TEA) as confirmed by spectrophotometric and spectrofluorimetric studies. The pKa values of P1, P2 and P3 were found to be 4.00, 4.34 and 3.68 respectively and probes P1 and P2 are highly dynamic during acid-base switching behaviour. The TGA analysis reveals that probe P1 is more stable compared to P2 and P3. The photophysical and protonation mechanisms were studied through DFT/TD-DFT calculations. The acid base switching behavior was successfully defined at three different levels: solid state, solution, and Whatman filter paper loaded with probe.