Exploration of intramolecular charge transfer in para-substituted nitrobenzofurazan: Experimental and theoretical analyses

The present work aims at exploring the high electrophilic character of 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) toward the morpholine group by an SNAr reaction in acetonitrile or water (thereafter referred to as NBD-Morph). The electron-donating ability of the morpholine causes intra-molecular charge transfer (ICT). In this report, we present a comprehensive study on the optical characteristics using UV-Vis, photoluminescence (cw-PL) and its time-resolved (TR-PL) to determine the properties of the emissive intramolecular charge transfer (ICT) in the NBD-Morph donor-acceptor system. An exhaustive theoretical investigation utilizing the density functional theory (DFT) and its extension TD-DFT methods is an essential complement of experiments to rationalize and understand the molecular structure and related properties. The findings from QTAIM, ELF, and RDG analyses establish that the bonding between morpholine and NBD moieties is of the electrostatic or hydrogen bond type. In addition, the Hirshfeld surfaces have been established to explore the types of interactions. Further, the non-linear optical (NLO) responses of the compound have been examined. The struc-ture-property relationships obtained through the combined experimental and theoretical offer valuable insights for designing efficient NLO material.

Automated summary

This work focuses on investigating the high electrophilic character of 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) towards the morpholine group through an SNAr reaction in acetonitrile or water (referred to as NBD-Morph). The electron-donating ability of morpholine leads to intra-molecular charge transfer (ICT). UV-Vis, photoluminescence (cw-PL), and time-resolved photoluminescence (TR-PL) are used to comprehensively study the optical characteristics and properties of the emissive intramolecular charge transfer (ICT) in the NBD-Morph donor-acceptor system. The findings from theoretical investigations, including density functional theory (DFT) and its extension TD-DFT methods, provide valuable insights into the molecular structure and related properties, complementing the experimental results.