Spectroscopy and fluorescence lifetime imaging in live cells of a cyano-substituted combretastatin

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 crosssection,and suggests potential routes to the design of a molecule that could be effectively activated by photoisomerisation in a two-photon process.