Phenanthridine‐Based Donor/Acceptor Fluorescent Dyes: Synthesis, Photophysical Properties and Fluorometric Sensing of Biogenic Primary Amines

Abstract Synthesis of two new and straight forward phenanthridine based fluorophores ( PA1 and PA2 ) have been described. The molecular structure of PA1 and PA2 was confirmed by spectroscopic studies ( 1 H NMR, 13 C NMR and HRMS). The dyes are further characterized by comprehensive photophysical study, and their data are critically analyzed. The fluorescence properties of these D−A chromophores are highly influenced by the position of the hydroxyl substitution and the solvent polarity. These probes exhibited an arsenal of advantageous features such as higher Stokes shift values and appreciable photostability. Compounds PA1 and PA2 are found to be indicating fluorescent ratiometric detection towards primary amines (PAs) with high selectivity and sensitivity. With this background, sensing of PAs was extended to biogenic amines as they have primary amine functionality. As expected, these fluorophores have excellent detection ability towards neurotransmitters, such as dopamine (DA) and serotonin (SN) with a low limit of detection (LOD) such as 1.61 nM and 0.31 nM respectively. The sensing mechanism of the probe PA1 with PAs are based on the nucleophilic addition and confirmed through investigation by 1 H NMR titration, mass analysis and theoretical calculations. Moreover, sensor probe PA1 based test paper strip was developed, which could detect DA conveniently when visualized under 365 nm UV lamp.