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Crystallization induced reversible fluorescence switching and alkyl chain length dependent thermally stable supercooled organic fluorescent liquid

Abstract

Highly stable supercooled fluorescent liquid and crystallization induced reversible fluorescence switching has been achieved via varying alkyl chain length of alkoxy group in triphenylamine aldehyde, (4-(diphenylamino)-methoxybenzaldehyde (DPAMB). DPAMB and different alkyl chain, ethyl (DPAEB), propyl (DPAPrB), butyl (DPABB), pentyl (DPAPeB), hexyl (DPAHB) and cyanohexyl (DPAH-CNB) substituted compound exhibited weak fluorescence (max between 429 and 490 nm) in the solid state except DPAEB that did not show any measurable fluorescence. Structural analysis were performed to get the insight of alkyl chain length effect on the molecular packing in the solid state. The strong crushing of all solids lead to drastic enhancement of fluorescence intensity without altering max. Interestingly, the melt of all compounds showed strong fluorescence with red shift of fluorescence max (460 – 489 nm). Slight rubbing of the melted solids exhibited reversible fluorescence switching. Powder X-ray diffraction (PXRD) studies suggested the conversion of crystalline to amorphous and vice versa while melting of solids and rubbing of melt was responsible fluorescence switching. Importantly, the melt showed alkyl chain length dependent stable supercooled fluorescent liquid at room temperature. Differentail scanning caolorimetry (DSC) indicated crystallization of melt while heating/cooling of DPAMB and DPEB melt whereas DPAPrB, DPABB, DPAPeB, DPAHB and DPAH-CNB did not show any crystallization in the subsequent cooling/heating cycles. Thus alkyl chain length and propeller molecular shape of triphenylamine has been utilized for developing strongly fluorescent supercooled fluorescent liquid at room temperature.

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Publication details

The article was received on 14 Sep 2017, accepted on 10 Oct 2017 and first published on 10 Oct 2017


Article type: Paper
DOI: 10.1039/C7CE01650F
Citation: CrystEngComm, 2017, Accepted Manuscript
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    Crystallization induced reversible fluorescence switching and alkyl chain length dependent thermally stable supercooled organic fluorescent liquid

    P. S. Hariharan, D. Moon and P. P. Anthony, CrystEngComm, 2017, Accepted Manuscript , DOI: 10.1039/C7CE01650F

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