title: Photophysical investigation of cyano-substituted terrylenediimide derivatives.
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.
authors.affiliation: Molecular Imaging and Photonics, Department of Chemistry, Katholieke Universiteit Leuven , Celestijnenlaan 200F, 3001 Leuven, Belgium.
authors.forename: Koen
authors.initials: K
authors.lastname: Kennes
authors.forename: Yannick
authors.initials: Y
authors.lastname: Baeten
authors.forename: Tom
authors.initials: T
authors.lastname: Vosch
authors.forename: Wouter
authors.initials: W
authors.lastname: Sempels
authors.forename: Stoyan
authors.initials: S
authors.lastname: Yordanov
authors.forename: Sebastian
authors.initials: S
authors.lastname: Stappert
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.forename: Klaus
authors.initials: K
authors.lastname: Müllen
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Mark
authors.initials: M
authors.lastname: Van der Auweraer
authors.forename: Eduard
authors.initials: E
authors.lastname: Fron