S•••π, π−π and C−H•••π Contacts Regulate Solid State Fluorescence in Regioisomeric Bisthiazolylpyrenes

Abstract

The formation of well-defined packing motifs and control of π–π stacking by rationalizing the effects of molecular substitution in π-conjugated organic materials represent a significant challenge in supramolecular design. To explore the influence of the thiazolyl group in the solid state packing and photophysical properties of pyrene, a new class of three regioisomeric bisthiazolylpyrenes (2-2″TP) were designed and synthesized. Single crystal X-ray structure and quantum theory of atoms in molecules analysis revealed the presence of S···π interactions in 2′TP. Hirshfeld analysis showed the γ and β packing motif in 2TP and 2″TP, respectively, due to extensive π–π interactions, observed S···π interactions led to herringbone packing in 2′TP. The diverse packing arrangement of 2-2″TP led to a notable difference in the fluorescence behavior in the crystalline state. 2′TP possessing S···π interaction showed remarkable enhanced emission in the crystalline state compared to the amorphous state, in contrast to 2TP and 2″TP. Our results provide new insight for the rational design and regulation of intermolecular interactions of conjugated heterocyclic aromatics to achieve a diverse degree of orbital overlap between neighboring chromophore units and thereby favorable optoelectronic properties.