Ingenious modification of molecular structure effectively regulates excited-state intramolecular proton and charge transfer: a theoretical study based on 3-hydroxyflavone

Harnessing ingenious modification of molecular structure to regulate excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) characteristics holds great promise in fluorescence sensing and imaging. Based on the 3-hydroxyflavone (3HF) molecule, 2-(2-benzo[b]furanyl)-3-hydroxychromone (3HB) and 2-(6-diethylamino-benzo[b]furan-2-yl)-3-hydroxychromone (3HBN) were designed by the extension of the furan heterocycle and the introduction of a diethylamino group. The analysis of important hydrogen bond length, frontier molecular orbitals, infrared spectra, and potential curves have cross-validated our results. The results indicate that proper site furan heterocycle extension and diethylamino donor group substitution not only shift the absorption and emission spectra to the red but also effectively modulate the excited-state dynamic behaviors. Strengthened ICT characteristics from 3HF to 3HB and to 3HBN make the occurrence of ESIPT increasingly difficult due to the higher energy barriers, which indicates that the ESIPT and ICT processes are competitive mechanisms. We envision that our work would open new windows for improving molecular properties and developing more fluorescent probes and organic radiation scintillators.