Peak two-photon molecular brightness of fluorophores is a robust measure of quantum efficiency and photostability

摘要

To date, the suitability of a fluarophore for applications involving two-photon absorption has generally been characterized by its two-photon cross-section. Here we consider the robustness and significance of an alternative measure termed the molecular brightness-the fluorescence emission per molecule-which can be obtained readily by use of photon-counting techniques such as fluorescence correlation spectroscopy. The peak molecular brightness attained with increasing excitation intensity is shown to be a reliable benchmark for various fluorescent dye solutions. This figure of merit is considered both theoretically and experimentally and found to be related to the two-photon quantum efficiency and the photostability properties of a dye solution, while it is independent of the solution's two-photon cross section. This benchmark carries considerable practical as well as scientific interest. (c) 2006 Optical Society of America.