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21 January 2015

New Publication Out

Photophysical Investigation of Cyano-Substituted Terrylenediimide Derivatives.

Koen Kennes, Yannick Baeten, Tom Vosch, Wouter Sempels, Stoyan Yordanov, Sebastian Stappert, Long Chen, Klaus Müllen, Johan Hofkens, Mark Van der Auweraer, and Eduard Fron. The Journal of Physical Chemistry. 118, 14662−14674 (2014) 
dx.doi.org/10.1021/jp5104577

Abstract
Two new terrylenediimide (TDI) chromophores with cyano substituents in the bay and core area (BCN-TDI and OCN-TDI, respectively) have been characterized by a wide range of techniques, and their applicability for stimulated emission depletion (STED) microscopy has been tested. By cyano substitution an increase of the fluorescence quantum yield and a decrease of the nonradiative rate constant is achieved and attributed to a reduced charge-transfer character of the excited state due to a lower electron density of the TDI core.

For BCN-TDI, the substitution in the bay area induces a strong torsional twist in the
molecule which, similar to phenoxy bay-perylenediimide (PDI), has a strong effect on the fluorescence lifetime but appears to prevent the aggregation that is observed for OCN-TDI. The single-molecule photobleaching stability of BCN- and OCN-TDI is lower than that of a reference TDI without cyano substitution (C7-TDI), although less so for OCN-TDI. The photophysical properties of the excited singlet state are only slightly influenced by the cyano groups.

The observed intense stimulated emission, the pump−dump−probe experiments, and STED single-molecule imaging indicate that STED experiments with the cyano-substituted TDIs are possible. However, because of aggregation and more efficient photobleaching, the performance of BCN- and OCN-TDI is worse than that of the reference compound without cyano groups (C7-TDI). Bay-substituted TDIs are less suitable for STED microscopy.

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