Controllable molecular aggregation and fluorescence properties of 1,3,4-oxadiazole derivatives

Abstract

The molecular self-assembly behaviour of 2,2'-Bis-(4-hexyloxyphenyl)-bi-1,3,4-oxadiazole (BOXD-6) in solution, on surfaces and in bulk crystals, and its photo-physical properties were studied via a combination of experimental techniques and theoretical calculations. It is found that BOXD-6 molecules self-assemble into both H-and J-aggregates at moderate concentration (~10 -4 M) and then transit to exclusive J-aggregates at higher concentration (~10 -3 M) in tetrahydrofuran. In H-aggregation (α polymorph), BOXD-6 adopts a linear conformation and forms a one-dimensional layered structure; in Jaggregation (β polymorph), it adopts a Z-shaped conformation and form a more ordered two-dimensional layered structure. A π-stacking structure is observed in both cases, and adjacent molecules in the J-aggregation show larger displacement along the molecular long axis direction than that in H-aggregation. Although J-aggregates are almost the only component in concentrated solutions (10 -3 M), both H-and J-aggregates can be obtained if concentrated solution is transformed onto substrates through a simple drop-casting method. Such a phase transition during film formation can be easily avoided by adding water as precipitator; a film with pure J-aggregates is then obtained. In order to get more information on molecular self-assembly, intermolecular interaction potential energy surfaces (PES) were evaluated via theoretical calculations at the DFT level (M062x/6-31G**). The PES not only confirm the molecular stacking structures found in crystals but also predict some other likely structures, which will be the target of future experiments Please do not adjust margins Please do not adjust margins molecular self-assembly on substrates. In order to get deeper understanding of the molecular self-assembly, the intermolecular interaction potential energy surfaces were also evaluated through theoretical calculations at the Density Functional Theory (DFT) level.In H-aggregation, BOXD-6 adopts a linear conformation and forms a one-dimensional layered structure; in J-aggregation, it adopts a Z-shaped conformation and form a more ordered two-dimensional layered structure.

π–π Noncovalent Interaction Involving 1,2,4- and 1,3,4-Oxadiazole Systems: The Combined Experimental, Theoretical, and Database Study

“…Moreover, the current finding on the π···π interactions involving oxadiazole moieties are important not only for the utilization of medicinal chemistry and drug design. Previously, such oxadiazole-involved stacking interactions were recognized as the properties defining force in several fluorescent materials [ 85 , 86 , 87 , 88 ].…”

Evolution of HJ Coupling in Nanoscale Molecular Self-Assemblies

“…Recent experimental work aimed at the realization of tunable HJ aggregate systems focused on manipulation of molecular packing through the addition of side chains and/or immersion in different dielectric environments. − ,,, Maity et al used the length of poly­(ε-caprolactone) grafted on graphene quantum dots to direct molecular packing, forming J and H aggregates . Egawa and co-workers immersed films of 5,10,15,20-tetrakis­(4-sulfonatiphenyl)­porphorhyrin (TPPS) and poly­(allylamine) in acidic and neutral solutions to induce a reversible J–H transition in the TPPS assemblies .…”

Polar Switching and Cybotactic Nematic Ordering in 1,3,4-Thiadiazole-Based Short-Core Hockey Stick-Shaped Fluorescent Liquid Crystals

“…This red shift is due to the development of the aggregated species with an increase in concentration of the monomer which suggests the formation of the aggregates from monomer concentration and the population of the J-aggregates increases. 25 Similarly, the red shift is also observed in DCM. Similar behavior was not observed in polar solvents such as tetrahydrofuran and acetonitrile.…”