TY - JOUR A1 - Tasior, M. A1 - Bald, Ilko A1 - Deperasinska, I. A1 - Cywinski, P.J. A1 - Gryko, D.T. T1 - An internal charge transfer-dependent solvent effect in V-shaped azacyanines JF - Organic & biomolecular chemistry N2 - 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. KW - Fluorescence spectroscopy KW - Dyes KW - Solvent effect PY - 2015 DO - https://doi.org/10.1039/c5ob01633a SN - 1477-0520 SN - 1477-0539 VL - 13 IS - 48 SP - 11714 EP - 11720 PB - RSC CY - Cambridge AN - OPUS4-35194 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -