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Issue 14, 2016
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Crystallization induced enhanced emission in conformational polymorphs of a rotationally flexible molecule

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Abstract

The crystallization of weakly fluorescent 4-amino-2,2′-bipyridine (AMBPY) in solution phase under ambient conditions afforded three fluorescent conformational polymorphs. The marginal increase in the barrier to rotation observed in AMBPY as compared to unsubstituted 2,2′-bipyridine could be attributed to the “buttressing effect” offered by the amino substituent at the meta position. A smaller yet significant difference in energy (0.1–2.6 kJ mol−1) with respect to the global minima facilitates the isolation of AMBPY-I–III polymorphs. A unique nitrogen–nitrogen interaction is observed in two of the polymorphs, namely, AMBPY-I and AMBPY-III, promoted by cooperative C⋯H and N⋯H interactions. A crystallization-induced enhancement (ca. 5–10 fold) in the fluorescence quantum yield of AMBPY polymorphs is observed relative to the solution/amorphous state. Controlling the luminescence properties of molecular solids by tuning their packing arrangements via various interactions is an integral aspect in the construction of novel photo-functional materials.

Graphical abstract: Crystallization induced enhanced emission in conformational polymorphs of a rotationally flexible molecule

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Supplementary files

Article information


Submitted
05 Oct 2015
Accepted
25 Nov 2015
First published
26 Nov 2015

J. Mater. Chem. C, 2016,4, 2931-2935
Article type
Paper
Author version available

Crystallization induced enhanced emission in conformational polymorphs of a rotationally flexible molecule

A. R. Mallia, R. Sethy, V. Bhat and M. Hariharan, J. Mater. Chem. C, 2016, 4, 2931
DOI: 10.1039/C5TC03188E

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