Resonance-Assisted Hydrogen Bonding and π–π Stacking Modulates the Charge Transfer Coupling in Crystalline Naphthothiazoles

Abstract

Supramolecular chemistry employs noncovalent interactions to coax π-conjugated molecules into ordered functional assemblies. Herein, we report 5-methoxynaphtho[1,2-d]thiazol-2-amine (NTN) and 4-bromo-5-methoxynaphtho[1,2-d]thiazol-2-amine (NTNB) assembled into π-stacked columns integrated by lateral resonance-assisted hydrogen bonds (RAHBs) orthogonal to the π–π stacking direction. Quantum theory of atoms in molecules (QTAIM) and interacting quantum atoms (IQA) analyses were utilized to characterize the presence and stability of intermolecular RAHBs in NTN and NTNB. In contrast to the parallel packing of NTN, bromine substitution promoted antiparallel packing in NTNB with noticeable π–π stacking and orbital overlap favoring efficient charge transfer coupling (Ve/h). Antiparallel stacking in NTNB exhibits a dipole moment minimization and aromaticity gain. The relevance of aromaticity in stabilizing π–π stacked systems is highlighted by the aromaticity gain in antiparallel stacked dimers of NTNB and can be extended to estimate the nature and strength of noncovalent interactions. Crystal packing plays a crucial role in regulating the charge transport properties, as can be observed from higher electron and hole transfer coupling along the π–π stacked and RAHB dimer, respectively, in NTN. However, in NTNB maximum electron and hole transfer coupling occurs selectively along the π–π stacked antiparallel dimer. The anisotropic mobility plots from a combination of first-principles quantum chemical calculations and the Marcus–Hush formalism confirm that both RAHB and π–π stacked dimers contribute to the mobility in NTN, but NTNB exclusively benefits from the π–π stacked dimer. Modulating noncovalent interactions for charge carrier transport can harness the innate potential of organic molecules to engineer novel optoelectronic materials.