Probing the ESIPT process in 2-amino-1,4-naphthoquinone: thermodynamics properties, solvent effect and chemometric analysis

Abstract

The developing of fluorescent probes for disease diagnosis is a very important task, which favors precision in the diagnosis and success in the treatment. Recently, amino-naphthoquinone derivatives showed to be efficient fluorescent probes for disease diagnosis. Those compounds exhibit excited-state intramolecular proton transfer (ESIPT), which is the main mechanism responsible for their use as fluorescent probes. The understanding of the ESIPT mechanism for naphthoquinones is an important way of developing more efficient and selective fluorescent probes. In this work, the ESIPT process for ANQ was performed at the TD-DFT/CAM-B3LYP/DGTZVP and DFT/B3LYP/DGTZVP level for the electronic and geometric studies. These parameters were selected for the PCA analysis. The solvent effect was investigated by using PCM and IEF-PCM in chloroform, water and methanol. 2-Amino-1,4-naphthoquinone (ANQ) showed blue emission for fluorescence, having keto–keto* absorption at 4.50 eV and the enol–enol* decay at 2.75 eV. The solvent effect was evaluated, and the ESIPT process of ANQ was favorable in nonpolar and polar solvents. Furthermore, the thermodynamics properties showed that the ESIPT is favorable with a proton transfer equilibrium constant of ~105.