Dual state emissive pyrene-fused benzopyrazaacenes and their solvatochromic behaviour

This study investigates how molecular orientation and microstructure influence the photophysical and electronic properties of pyrene-fused azaacenes. Four substituted pyrene-fused benzopyrazaacene compounds were synthesized via a single step cyclo condensation of K-conjugated pyrene quinone building blocks with 3,4-diaminobenzophenone. The synthesized molecules were characterized using IR, NMR spectroscopy and HRMS analysis. Photophysical and electrochemical properties were studied to explore the impact of molecular orientation and microstructure on the properties of pyrene-fused azaacenes. Substitutions at the 2, 7-positions of the pyrene core significantly affected the photophysical properties while demonstrating moderate solubility. Notably, the compounds exhibited pronounced solvatochromic effect across various solvents. Furthermore, the additional incorporation of a carbonyl moiety adjacent to the core expanded pyrene at the K-region resulted in dual state emission, influencing solid state emission accompanied by robust thermal stability. Theoretical calculations were performed to gain insights into the energy levels of the compound and its molecular orientation using time dependent density functional theory (TD-DFT).