Mechanochromism and Aggregation-Induced Emission in Phenanthroimidazole Derivatives: Role of Positional Change of Different Donors in a Multichromophoric Assembly

Abstract

Organic materials possessing solid-state emission responsive to external stimuli have significance in a variety of material, biomedical, and optoelectronic applications. Organic molecules having different donor–acceptor architectures integrated with aggregation-induced emission (AIE) fluorophores have been utilized in development of mechanofluorochromic (MFC) materials. In this work, we have designed and synthesized phenanthroimidazole (PI) based derivatives TPE-PI-1, TPE-PI-2, TPE-PI-3, PTZ-PI-1, PTZ-PI-2, and PTZ-PI-3 where in donors tetraphenylethylene-TPE (D) and phenothiazine-PTZ (D′) of contrasting donor abilities are attached to the N and C atom positions of PI. The position and mode of attachment of the donors have been changed, and an additional PTZ spacer has been introduced which has a direct consequence on their photophysical and electronic properties. The PI derivatives manifest AIE, solvatochromic, and mechanochromic behavior. The single crystal X-ray analysis of TPE-PI-1 and PTZ-PI-2 reveals bent structures for the PTZ unit and a twisted conformation for TPE moieties. The density functional theory calculations were used to obtain optimized ground-state structures of the PI derivatives. The work shows a comprehensive comparison of the photophysical, electronic, AIE, and MFC properties of the PI derivatives as an effect of variations in the position of donor, donor–acceptor strength, and change in molecular conformation on use of spacer.