To date, the suitability of a fluorophore 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.
© 2006 Optical Society of America
Original Manuscript: November 22, 2005
Revised Manuscript: February 6, 2006
Manuscript Accepted: February 17, 2006
Vol. 1, Iss. 8 Virtual Journal for Biomedical Optics
Vijay Iyer, Molly J. Rossow, and M. Neal Waxham, "Peak two-photon molecular brightness of fluorophores is a robust measure of quantum efficiency and photostability," J. Opt. Soc. Am. B 23, 1420-1433 (2006)