Issue 48, 2015

An internal charge transfer-dependent solvent effect in V-shaped azacyanines

Abstract

New V-shaped non-centrosymmetric dyes, possessing a strongly electron-deficient azacyanine core, have been synthesized based on a straightforward two-step approach. The key step in this synthesis involves palladium-catalysed cross-coupling of dibromo-N,N′-methylene-2,2′-azapyridinocyanines with arylacetylenes. The resulting strongly polarized π-expanded heterocycles exhibit green to orange fluorescence and they strongly respond to changes in solvent polarity. We demonstrate that differently electron-donating peripheral groups have a significant influence on the internal charge transfer, hence on the solvent effect and fluorescence quantum yield. TD-DFT calculations confirm that, in contrast to the previously studied bis(styryl)azacyanines, the proximity of S1 and T2 states calculated for compounds bearing two 4-N,N-dimethylaminophenylethynyl moieties establishes good conditions for efficient intersystem crossing and is responsible for its low fluorescence quantum yield. Non-linear properties have also been determined for new azacyanines and the results show that depending on peripheral groups, the synthesized dyes exhibit small to large two-photon absorption cross sections reaching 4000 GM.

Graphical abstract: An internal charge transfer-dependent solvent effect in V-shaped azacyanines

Supplementary files

Article information

Article type
Paper
Submitted
05 Aug 2015
Accepted
07 Oct 2015
First published
08 Oct 2015

Org. Biomol. Chem., 2015,13, 11714-11720

Author version available

An internal charge transfer-dependent solvent effect in V-shaped azacyanines

M. Tasior, I. Bald, I. Deperasińska, P. J. Cywiński and D. T. Gryko, Org. Biomol. Chem., 2015, 13, 11714 DOI: 10.1039/C5OB01633A

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