Structure-mechanical property correlations in mechanochromic luminescent crystals of boron difluoride dibenzoylmethane derivatives

Krishna, Gamidi Rama and Devarapalli, Ramesh and Prusty, Rajesh and Liu, Tiandong and Fraser, Cassandra L and Ramamurty, Upadrasta and Reddy, Chilla Malla (2015) Structure-mechanical property correlations in mechanochromic luminescent crystals of boron difluoride dibenzoylmethane derivatives. In: IUCrJ, 2 (6). pp. 611-619.

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Abstract

The structure and mechanical properties of crystalline materials of three boron difluoride dibenzoylmethane (BF(2)dbm) derivatives were investigated to examine the correlation, if any, among mechanochromic luminescence (ML) behaviour, solid-state structure, and the mechanical behaviour of single crystals. Qualitative mechanical deformation tests show that the crystals of BF(2)dbm(Bu-t)(2) can be bent permanently, whereas those of BF(2)dbm(OMe)(2) exhibit an inhomogeneous shearing mode of deformation, and finally BF(2)dbmOMe crystals are brittle. Quantitative mechanical analysis by nanoindentation on the major facets of the crystals shows that BF(2)dbm(Bu-t)(2) is soft and compliant with low values of elastic modulus, E, and hardness, H, confirming its superior suceptibility for plastic deformation, which is attributed to the presence of a multitude of slip systems in the crystal structure. In contrast, both BF(2)dbm(OMe)(2) and BF(2)dbmOMe are considerably stiffer and harder with comparable E and H, which are rationalized through analysis of the structural attributes such as the intermolecular interactions, slip systems and their relative orientation with respect to the indentation direction. As expected from the qualitative mechanical behaviour, prominent ML was observed in BF(2)dbm(Bu-t)(2), whereas BF(2)dbm(OMe)(2) exhibits only a moderate ML and BF(2)dbmOMe shows no detectable ML, all examined under identical conditions. These results confirm that the extent of ML in crystalline organic solid-state fluorophore materials can be correlated positively with the extent of plasticity (low recovery). In turn, they offer opportunities to design new and improved efficient ML materials using crystal engineering principles.

Item Type:	Journal Article
Publication:	IUCrJ
Publisher:	INT UNION CRYSTALLOGRAPHY
Additional Information:	Copy right for this article belongs to the INT UNION CRYSTALLOGRAPHY, 2 ABBEY SQ, CHESTER, CH1 2HU, ENGLAND
Keywords:	crystal engineering; intermolecular interactions; mechanochromism; mechanical properties; nanoindentation; organic solid-state reactions; hydrogen bonding
Department/Centre:	Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited:	10 Dec 2015 06:07
Last Modified:	10 Dec 2015 06:07
URI:	http://eprints.iisc.ac.in/id/eprint/52878

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