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A fluorenylidene-acridane that becomes dark in color upon grinding – ground state mechanochromism by conformational change

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Abstract

We report mechanochromic color change controlled by conformational change (between folded and twisted conformers) of fluorenylidene-acridanes (FAs). FAs with four N-alkyl groups (methyl, ethyl, n-butyl and n-octyl) were synthesized via the Barton–Kellogg reaction of diazofluorene and electrophilic N-tert-butoxy carbonyl thioacridone, deprotection of the tert-butoxy carbonyl group gives fluorenylacridine, and alkylation on the nitrogen atom is done using alkyl tosylate or triflate. FAs were characterized by NMR, UV-vis absorption and photoluminescence spectroscopy, theoretical calculation, cyclic voltammetry, and powder and single-crystal X-ray analyses. The color and folded/twisted conformation of the FAs were changed by the choice of substituent on the nitrogen atom, physical state (solution or solid), and morphology (crystalline or amorphous). Grinding of N-methyl FA solids, using an agate mortar, caused the morphology to change from a crystalline to amorphous state, which induced a conformational change from the folded to the twisted conformer, and a mechanochromic color change from yellow to dark green. The reverse color change, along with a morphological and conformational change to the folded conformer, was performed by solvent vapor exposure (chloroform). The twisted and folded conformers showed ambipolar (hole/electron) and hole-only transport properties, respectively.

Graphical abstract: A fluorenylidene-acridane that becomes dark in color upon grinding – ground state mechanochromism by conformational change

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Publication details

The article was received on 15 Aug 2017, accepted on 24 Oct 2017 and first published on 14 Nov 2017


Article type: Edge Article
DOI: 10.1039/C7SC03567E
Citation: Chem. Sci., 2018, Advance Article
  • Open access: Creative Commons BY license
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    A fluorenylidene-acridane that becomes dark in color upon grinding – ground state mechanochromism by conformational change

    T. Suzuki, H. Okada, T. Nakagawa, K. Komatsu, C. Fujimoto, H. Kagi and Y. Matsuo, Chem. Sci., 2018, Advance Article , DOI: 10.1039/C7SC03567E

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