Issue 48, 2016

Fluorescent mesomorphic pyrazinacenes


We report the synthesis of highly fluorescent pyrazinacenes (6,13-dihydrohexaazapentacene; fluorubine) containing groups at 6,13 positions that promote their solubility in non-polar organic solvents and their self-assembly properties. Hydrophilic 3,4,5-tris[2-[2-(2-methoxyethoxy)ethoxy]ethoxy]benzyl (TEG3Bz) and hydrophobic 3,4,5-tris(1-n-dodecyloxy)benzyl (C123Bz) groups were incorporated in a series of compounds 1–9 where the fluorubine core was modified either by 2-bromination or by introduction of four peripheral benzo groups. Thus, 1–3 are respectively hydrophilic 6,13-(TEG3Bz)2, hydrophobic 6,13-(C123Bz)2 and amphiphilic 6-(TEG3Bz)(C123Bz) with 4–6 being the corresponding 2-brominated compounds and 7–9 the corresponding [a,c,l,n]-tetrabenzo compounds. Several of the compounds exhibit thermotropic mesophases: 4 and 7 have lamellar structures even at room temperature; 8 and 9 form columnar rectangular phases at higher temperatures. All the compounds are highly fluorescent exhibiting quantum yields (QY) up to 60% in solution. Solid state fluorescence spectra reveal that while the unmodified 6,13-dihydrohexaazapentacene compounds 1–3 maintain their large QYs in the solid state, 2-bromination (4–6) reduces the QY substantially (to 10% approx.). 7–9 give QY similar to 1–3 in solution but their QYs are attenuated in solid state due to chromophore aggregation.

Graphical abstract: Fluorescent mesomorphic pyrazinacenes

Supplementary files

Article information

Article type
25 Oct 2016
18 Nov 2016
First published
21 Nov 2016
This article is Open Access
Creative Commons BY license

J. Mater. Chem. C, 2016,4, 11514-11523

Fluorescent mesomorphic pyrazinacenes

G. J. Richards, S. Ishihara, J. Labuta, D. Miklík, T. Mori, S. Yamada, K. Ariga and J. P. Hill, J. Mater. Chem. C, 2016, 4, 11514 DOI: 10.1039/C6TC04628B

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