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While checking two photon microscopy, the use of high flux femtosecond laser is required for the dual absorption of photons, due to the low probability of these two photons being absorbed. Is there any way of modifying molecular electronic structure to increase this probability?

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  • $\begingroup$ I cannot write a nice answer because I lack the basics of the optics involved, as well as the quantum mechanical tool linking structures to the phenomenon. However, as a fact, modifications are certainly pursued and in most cases starting from well know dyes, or conjugated polymers, or even short or small conjugated systems. Substitution with electron donor and acceptor groups leading to internal charge transfer is a recurrent modification. At least, one rationale is a very high absorption coeff already for the first absorption, as whatever happens to the "first" photon influences the TPA $\endgroup$
    – Alchimista
    Jul 14, 2021 at 9:23
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    $\begingroup$ People have been using nanoparticles to "enhance" two photon fluorescence. This is so-called plasmonic enhancement. If you recall Raman spectroscopy, a similar effect surface enhanced plasmon resonance increases the intensity of Raman scattering. Search these keywords. $\endgroup$
    – AChem
    Jul 14, 2021 at 16:25
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    $\begingroup$ There is an excellent article that addresses your question is great detail- the design requirements for two-photon fluorescence "Two-Photon Absorption and the Design of Two-Photon Dyes". Go to Google Scholar and search this title. $\endgroup$
    – AChem
    Jul 14, 2021 at 16:31
  • $\begingroup$ BTW, one of the simplest ways to increase two-photon absorption is decreasing temperature. See pubs.acs.org/doi/10.1021/jp303789s and pubmed.ncbi.nlm.nih.gov/17583328 (which mentions molecular conformation change with temperature). $\endgroup$ Jul 15, 2021 at 22:51

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