Fluorescent Diarylethenes With Polar Groups: Synthesis, Spectra, and Optical Microscopy Applications

The use of photoactivatable fluorescent diarylethenes (fDAEs) in biology-related light microscopy has been restricted by the lack of probes having freely variable structural and spectral properties. Facing these challenges, we synthesized "turn-on" fDAEs with four hydroxyl groups and a single functionality in the core structure (HO-fDAEs). HO-fDAEs emit green light; they were used for the preparation of cell-permeant mitochondrion-selective probes and bioconjugation with proteins (via a single COOH group). HO-fDAEs were combined in bio-imaging with a thiophene-substituted fDAE (Th-fDAE) possessing red-shifted absorption and emission bands of the open- and closed-ring isomers. Th-fDAE undergoes full on-switching with 405 nm and excitation with green light (< 560 nm). The large Stokes shifts of HO-and Th-fDAE (80 and 110 nm, respectively) and different excitation wavelengths permitted color separation in optical microscopy. Photoactivation of HO-fDAEs and transient on-off switching (blinking) of Th-fDAE made it possible to acquire two-color images of cellular structures with optical superresolution.