Triplet excited states, ubiquitous in organic chromophores, can be accessed through various pathways. The feasibility of each pathway is determined by the molecular and electronic structures of the organic chromophores.

Unprecedented multimodal weak interactions are quintessential to create novel supramolecular topologies. Among the plethora of weak interactions, halogen− halogen (X•••X) interactions offer innovative possibilities for the design of multidimensional scaffolds. Herein, we chronicle the state-of-the-art 1D, 2D, and 3D zipper motifs steered by distinct interhalogen interactions, revealing the potential of halogen bonding in engineering biomimetic molecular assemblies. Recurring units of Br 4 synthon, framed by type I and type II atom efficient X•••X interactions in a dibromonaphthathiazole derivative, 2,4-dibromo-5ethoxynaphtho[1,2-d]thiazole (NTB 2 ), forges the molecular zipper. On the basis of the semiclassical Marcus theory of charge transport, the NTB 2 zipper assembly displays selective electron transport along the type II X•••X bonded direction. Band structure analysis classified the crystalline NTB 2 as a wide band gap semiconductor with a band gap of 2.80 eV, respectively. The robustness of the X•••X mediated zipper motif opens up new avenues in the development of advanced functional materials.

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 (V e/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.

Excited state aromaticity is a stimulating area of research, widely used as a probe to describe and rationalize many photochemical phenomena. Herein, we review some of the recent findings of unprecedented aromatic stabilization in spin singlet excimer and through-space aromatic character in triplet excimers of a series of linear [n]acenes, as paramount examples of polycyclic aromatic hydrocarbons (PAHs). This review also provides insights on the

We systematically altered the molecular structure of 5-methoxynaphtho [1,2-d]thiazole (NTH) by replacing the terminal hydrogen atom with halogens (Cl, Br, I) to study the effect of single-atom substitution in modulating the crystal packing and optical band gap. The parent compound (NTH) and Br and I derivatives of NTH crystallized in the same space group, wherein only Br-and I-substituted molecular crystals displayed isostructural interaction topologies. The crystal-packing similarities in structurally equivalent motifs were established using the numerical descriptors isostructurality (I s ) and cell similarity (π) indices. An energy framework analysis was implemented to obtain a qualitative picture of the 3D topology displaying the predominant interactions in supramolecular architectures of the NTH derivatives. A decrease in optical band gap from 3.48 to 3.07 eV was observed with an increasing atomic number of halogens in NTH derivatives, signifying the direct role of halogen atoms in the electronic properties of organic crystals. The reduction of the optical band gap in 5-methoxynaphtho [1,2-d]thiazole derivatives was visualized from the band structure and projected density of states obtained by employing DFT calculations. The outcome suggests the potential of halogenation in tailoring the optoelectronic properties of organic functional materials.

Multitudes of novel π-conjugated materials have gained tremendous attention with potential applications in next-generation electronic devices as they are chemically programmable, mechanically flexible, and lightweight. Modulating the intermolecular interactions emerging from the π-conjugated molecules govern crystal packing and plays a pivotal role in designing molecular organic semiconductors. Determining the dynamic origin of charge transport in organic crystals from a molecular perspective has often proved challenging. In this Perspective, we have compiled effective methods to regulate the charge transport characteristics of functional organic materials in their crystalline phase. The ardent efforts in designing advanced materials with desirable charge transport properties from a theoretical perspective by our group are emphasized.

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