Computational Design, Synthesis, and Structure Property Evaluation of 1,3-Thiazole-Based Color-Tunable Multi-heterocyclic Small Organic Fluorophores as Multifunctional Molecular Materials

Probing
the chemical space of luminescent organic materials built
on novel cores is highly imperative for its potential to expand the
horizons of advanced functional materials. Small organic fluorophores
possessing therapeutic traits can contribute to theranostics. We coupled
computational and classical synthetic chemistry strategies for the
rational design of 5-(hetero-2-yl)-1,3-thiazoles as color-tunable
fluorophore core. With the aid of DFT and TD-DFT, we prove that the
multi-heterocyclic system is built on a thiazole–het core with
three inherent tunable sites on thiazole (C2, C4, and C5) capable
of accommodating a panoply of substituents as a multifunctional molecular
materials’ platform. This de novo design offered unprecedented
freedom to control strength and direction of charge transfer by varying
donor–acceptor fragments. A 30-member fluorophore library built
on thiazole-thiophene/furan core was accomplished using commercial
reagents by a simple [4 + 1] synthesis. Structure–photophysical
property studies revealed large Stokes shift, positive solvatochromism,
acidochromism, and color tunability in different solvents and were
rationalized using computational calculations. In vitro studies indicated 1a to be active against HL-60 cell lines, suggesting the possibility
of expanding the core for theranostics. The lower values of computed
hole reorganization energies indicated their potential as hole transporting
materials in optoelectronics and widen the scope of these molecules
as advanced functional materials.