Molecular construct for multiphoton fluorescence microscopy imaging

A molecular construct for multiphoton fluorescence microscopy imaging, wherein said molecular construct has a first, non-fluorescent configuration (2PAP-C) and a second, fluorescent configuration (2PAP-CL), wherein said molecular construct comprises:

• a two-photon absorbing probe (2PAP) having an emission spectrum, and
• a photochromic molecule linked to the two-photon absorbing probe (2PAP), wherein said photochromic molecule has a first colored isomeric form (C) and a second colorless isomeric form (CL), wherein said first colored isomeric form (C) has a first absorption spectrum that overlaps the emission spectrum of said two-photon absorbing probe (2PAP) such that the first colored isomeric form (C) photoisomerizes to said second colorless isomeric form (CL) upon absorption of two photons by said two-photon absorbing probe (2PAP), wherein of said second colorless isomeric form (CL) has a second absorption spectrum that does not overlap said emission spectrum of said two-photon absorbing probe (2PAP), and wherein said second colorless isomeric form (CL) isomerizes to said first colored isomeric form (C) by thermal isomerization.