Probing kinetic and thermodynamic parameters as well as solvent and substituent effects on spectroscopic probes of 2-amino-1,4-naphthoquinone derivatives

Abstract

In the world, many diseases, such as cancer, require rapid diagnosis. Currently, it is well known that fluorescent spectroscopy is one of the most promising methodologies to this end, because it is less invasive, rapid and quite sensitive. In this perspective, naphthoquinone derivatives have demonstrated applications as fluorescent probes. Despite great importance of substituents effects on the fluorescence mechanism, such as the ESIPT process, few detailed computational works on this subject have appeared. Our current findings showed that the ESIPT process is a preferential fluorescence mechanism in a great number of molecules. The compounds showed color emission ranging from red to green and blue to violet. Furthermore, PCA techniques have been employed for rationalizing the energy gaps of the fluorescence process of 36 naphthoquinone (ANQ) derivatives. The PCA referent emission energy showed bathochromic effects when electron donor groups were at position R3 or R5 and hypsochromic effects when withdrawing groups were in the same position. Our findings point out that substituents with higher electron density promote wavelength red-shifting. In fact, the substituent effects provide an understanding about behavior of the ESIPT process in ANQ derivatives, and how kinetic and thermodynamic parameters can be influenced. These conclusions can help in understanding emission and absorption energies as well as the solvent and substituent influence on the spectroscopic parameters.