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Mechano-responsive luminescent emissions of an organic molecular crystal: Effects of aromatic stacking interactions and solid state packing

Abstract

Three polymorphic forms, with different solid state luminescent emissions, were obtained from 2-hydroxynaphthaldehyde semicarbazone (2-NOH-S). In the pristine form, 2-NOH-S exhibited bright green emissions, while the C-M form obtained from methanol was non-emissive and the C-T form obtained from tetrahydrofuran exhibited weak yellow emissions. Our studies revealed that gentle mechanical grinding of either C-M or C-T forms produced the bright green emissive form with em 492 nm and 527 nm. Slurry conversion experiments revealed a monotropic relationship between the three polymorphic forms of 2-NOH-S, with the pristine form being most stable. More interestingly, we found that successive application of mechanical and chemical stimuli triggered reversible phase transitions between C-M and C-T forms and the green emissive phase. Based on spectroscopic, thermal and powder x-ray diffraction studies, we suggested that the mechano-luminescent transformation of C-M and C-T forms to the bright green phase resulted from reduction in the aromatic stacking interactions, and disruption of non-radiative vibrational decay pathways through the formation of stronger hydrogen bonds.

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Publication details

The article was received on 30 Apr 2019, accepted on 09 Jul 2019 and first published on 10 Jul 2019


Article type: Paper
DOI: 10.1039/C9CE00659A
CrystEngComm, 2019, Accepted Manuscript

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    Mechano-responsive luminescent emissions of an organic molecular crystal: Effects of aromatic stacking interactions and solid state packing

    K. Devi and R. J. Sarma, CrystEngComm, 2019, Accepted Manuscript , DOI: 10.1039/C9CE00659A

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