Integration of X-ray crystallography, density functional theory (DFT), and photophysical studies to understand aggregation-induced enhanced emission (AIEE) in dimethoxy acrylonitrile derivatives with donor-acceptor and donor-donor structures

Abstract

Here, the effect and importance of the molecular aggregation and electronic structure on the solid-state emission properties of the dimethoxy acrylonitrile derivatives were investigated in detail with the help of single crystal xray crystallography, photophysical studies, and Density Functional Theory. In this work, it was revealed that the most important parameters to be considered are the type of molecular pi & ctdot;pi stacking interactions and the presence of donor-acceptor moieties incorporated into the backbone of the molecule. Because of the varying substituents attached to the molecular skeleton's terminal side, the molecules' crystallographic geometric details differ, leading to distinct photophysical properties in the solid phase for each molecule. The study's results strongly validate the AIEE nature of all studied molecules. The contributions to the AIEE process arise from the structure of the molecules in terms of their electronegative and electropositive regions that create D-pi-A- pi-A and D-pi-A- pi-D depending on the additional fragments to the terminal sides of the molecules, restriction of intramolecular motion (RIM) mechanism created by noncovalent interactions, highly planarization based on molecular geometry and the types of the aggregation phase including, T, H and J type pi & ctdot;pi stacking interactions. The molecules having the highly planar molecular structure, strong pi & ctdot;pi stacking interactions of helical H type and regular H type, and the presence of halogen atoms show considerable AIEE in the solid phase with the help of the SCXRD, DFT, and photophysical studies. Based on our study, the unique features and easy bonding of the dimethoxy acrylonitrile derivatives with other units or moieties, they could be promising for applications in optoelectronic devices, chemosensors, and biological imaging due to the increasing PL emission in their solid phase used as a device in the real world.