Multiphoton excited fluorescent materials for frequency upconversion emission and fluorescent probes

Recent progress in developing various strategies for exploiting efficient MPA fluorophores for two emerging technological MPA applications including frequency upconversion photoluminescence and lasing as well as 2PA fluorescence bioimaging and biosensing are presented. An intriguing application of MPA frequency-upconverted lasing offers opportunity for the fabrication of high-energy coherent light sources in the blue region which could create new advantages and breakthroughs in various laser-based applications. In addition, multiphoton excitation has led to considerable progress in the development of advanced diagnostic and therapeutic treatments; further advancement is anticipated with the emergence of various versatile 2PA fluorescence probes. It is widely appreciated that the two-photon excitation offers significant advantages for the biological fluorescence imaging and sensing which includes higher spatial resolution, less photobleaching and photodamage as well as deeper tissue penetration as compared to the one-photon excited microscopy. To be practically useful, the 2PA fluorescent probes for biological applications are required to have a site-specificity, a high fluorescence quantum yield, proper two-photon excitation and subsequent emission wavelengths, good photodecomposition stability, water solubility, and biocompatibility besides large 2PA action cross-sections.