Affiliations: Central Laser Facility, Research Complex at Harwell, STFC Rutherford Appleton Laboratory, Harwell Oxford, UK | Biomedical Research Centre, University of Salford, Salford, UK
Note:  Corresponding author: Prof. Roger H. Bisby, School of Environment and Life Sciences, University of Salford, Salford M5 4WT, UK. Tel.: +44 0161 295 4912; E-mail: [email protected]
Abstract: Fluorescence lifetime imaging has been used to observe the real-time uptake in live mammalian cells of a combretastatin-type drug analogue that is a substituted stilbene with a cyano group at the bridging olefinic bond. Fluorescence spectra in a range of solvents show that this molecule has a substantial increase in dipole moment on promotion to the first excited singlet state that is indicative of intramolecular charge transfer (CT) from the methoxy substituents on the aromatic rings to the electron-withdrawing cyano group. This CT process is also demonstrated in picosecond time-resolved infrared measurements. Consistent with these observations, the molecule has been found to have a large two-photon absorption cross-section, and suggests potential routes to the design of a molecule that could be effectively activated by photoisomerisation in a two-photon process.