We introduce fluorescence-detected pump-probe microscopy by combining a wavelength-tunable ultrafast laser with a confocal scanning fluorescence microscope, enabling access to the femtosecond time scale on the micrometer spatial scale. In addition, we obtain spectral information from Fourier transformation over excitation pulse-pair time delays. We demonstrate this new approach on a model system of a terrylene bisimide (TBI) dye embedded in a PMMA matrix and acquire the linear excitation spectrum as well as time-dependent pump-probe spectra simultaneously. We then push the technique toward single TBI molecules and analyze the statistical distribution of their excitation spectra. Furthermore, we demonstrate the ultrafast transient evolution of several individual molecules, highlighting their different behavior in contrast to the ensemble due to their individual local environment. By correlating the linear and nonlinear spectra, we assess the effect of the molecular environment on the excited-state energy.

Center for Nanosystems Chemistry Universität Würzburg Theodor Boveri Weg 97074 Würzburg Germany

Faculty of Mathematics and Physics Charles University Ke Karlovu 5 121 16 Prague Czech Republic

Institut für Organische Chemie Universität Würzburg Am Hubland 97074 Würzburg Germany

Institut für Physikalische und Theoretische Chemie Universität Würzburg Am Hubland 97074 Würzburg Germany

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Interferometric excitation fluorescence lifetime imaging microscopy