Turn-On Mode Fluorescence Switch by Using Negative Photochromic Imidazole Dimer.

The development of fluorescence switchable molecules in several polar and apolar environments has been required for fluorescence imaging of nanostructures. Photochromic molecules are an important class for the reversible light-triggered fluorescence switching. Although many studies of fluorescence switching by using photochromic reactions have been reported, the report of photochromic molecules reversibly showing turn-on mode fluorescence switching has been limited in spite of their importance. Herein, we report the photoactivatable fluorescence based on negative photochromism, where the absorption spectrum of the compound after irradiation is blue-shifted relative to that before irradiation. We introduced naphthalimide units as a green fluorophore to the negative photochromic binaphthyl-bridged imidazole dimer. The fluorescence of the naphthalimide unit is efficiently quenched in the initial colored isomer (fluorescence quantum yield: Φ