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

Min Li, Haitao Wang, Fangyi Chen, Xiaoshi Jia, Huimin Liu, Xia Ran, Mahesh Kumar Ravva, Fuquan Bai, Songnan Qu, Hong-Xing Zhang, Jean-Luc Bredas

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

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 J-aggregation (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.
Original languageEnglish (US)
Pages (from-to)11681-11688
Number of pages8
JournalJ. Mater. Chem. C
Volume3
Issue number44
DOIs
StatePublished - 2015

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