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Issue 48, 2018
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Remarkable pressure-induced emission enhancement based on intermolecular charge transfer in halogen bond-driven dual-component co-crystals

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Abstract

A series of two-component co-crystals driven by I⋯N interactions based on the bipyridine (BIPY) chromophore with one among three different co-former building blocks, iodopentafluorobenzene (IPFB), 1,4-diiodotetrafluorobenzene (DITFB) and 1,3,5-trifluoro-2,4,6-triiodobenzene (IFB), were prepared and analysed via infared spectroscopy and single-crystal X-ray diffraction. By comparing the I⋯N distances in the co-crystal structures, we found that the higher the –F ratio in the building blocks the closer the contact of the I⋯N bond, enhancing the intermolecular interactions in these co-crystals as well. That is, the positive electrostatic potential on the iodine atom(s) in the co-formers was enhanced by the presence of strong electron-withdrawing groups. The distinct spectroscopic behaviours (fluorescence and Raman spectra) among the two-component BIPY co-crystal systems in response to hydrostatic pressure were also investigated. Interestingly, the fluorescence of BIPY–DITFB presented intriguing abnormal evolution from dark to bright, suggesting a new charge transfer state due to the decreased intermolecular distance and the enhanced I⋯N interactions. Theoretical simulations by Materials Studio also showed the shortened I⋯N distance and the increased angle of C–I⋯N, evidencing the enhanced I⋯N interactions. In contrast, BIPY–IFB showed only slightly enhanced fluorescence intensity at 550 nm consistent with BIPY–DITFB. Once the pressure was relieved, both the Raman and fluorescence spectra for BIPY co-crystal systems entirely self-recovered. Remarkable emission enhancement in a solid-state co-crystal has been rarely reported in previous publications and in fact, this study paves a unique way for designing and developing novel stimuli-responsive photo-functional materials.

Graphical abstract: Remarkable pressure-induced emission enhancement based on intermolecular charge transfer in halogen bond-driven dual-component co-crystals

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Publication details

The article was received on 12 Oct 2018, accepted on 12 Nov 2018 and first published on 26 Nov 2018


Article type: Paper
DOI: 10.1039/C8CP06363J
Citation: Phys. Chem. Chem. Phys., 2018,20, 30297-30303
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    Remarkable pressure-induced emission enhancement based on intermolecular charge transfer in halogen bond-driven dual-component co-crystals

    A. Li, J. Wang, Y. Liu, S. Xu, N. Chu, Y. Geng, B. Li, B. Xu, H. Cui and W. Xu, Phys. Chem. Chem. Phys., 2018, 20, 30297
    DOI: 10.1039/C8CP06363J

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