A novel fluorophore for two-photon-excited single-molecule fluorescence

We have studied the two-photon excited fluorescence properties of a new fluorophore, DCDHF-6, at single-molecule and bulk concentrations. This molecule features several beneficial properties including suppressed blinking, high fluorescence quantum yield, and viscosity-dependent fluorescence. Here, analysis of the two-photon excited fluorescence (TPF) behavior of single DCDHF-6 molecules demonstrates their applicability to experiments combining single-molecule and two-photon microscopy. A method is developed for measuring the absolute two-photon absorption cross-section δ of a single dye copy, and DCDHF-6 is shown to have a δ of 44 GM at an excitation wavelength of 940 nm.