TD-DFT calculations and optical properties of a luminescent thiazolopyrimidine compound with different emission colors and uncommon blue shift upon aggregation

Abstract

A thin film of 7-oxo-thiazolopyrimidine-3,8-dicarbonitrile derivative [7-ThPyDi]TF was prepared using a spin coating technique. The surface morphology and molecular structure are studied using various techniques such as XRD, FTIR, and scanning electron microscope (SEM). Moreover, the quantum chemical calculations were carried out through time-dependent density functional theory (TD-DFT) to investigate some reactivity descriptors such as softness and electronegativity. Also, Au/[7-ThPyDi]TF/p-Si/Al heterojunction diodes were fabricated. It was revealed that the energy bandgap value of [7-ThPyDi] as an organic thin film is 3.58 eV for direct transitions and 3.94 eV for indirect transitions, respectively, and this value falls within the semiconductor material range. The atomic force microscope demonstrated that the surface roughness of the thin film is approximately 32.2 nm. Because of its high refractive index, this material has the potential application as an antireflection coating for solar cells and as lenses with a wide focal range. We investigated a blue luminescent thiazolopyrimidine compound; the maximum emission in the more aggregated state (higher solution concentration) exhibits a notable blue shift compared to the more diluted solution. This uncommon phenomenon has been understood by structural analyses using density functional theory. The chemical structure of the molecule [planar conjugated cores and strong polar groups (–CO and –CN)] enables it to interact with both itself and the polar solvent. The intermolecular interactions result in the bending of the conjugated plane. As a result, the blue shift happens upon aggregation when the conjugated effect becomes weaker. The studied molecule gave different emission colors (blue, yellow, and reddish green) depending on the molecular packing.