The synergic control of photocyclization and fluorescence in a pH-gated photochromic system

• A pH-gated photochromism based on a rhodamine-modified diarylethene is explored.
• H+ acts as a key to modulate parallel and antiparallel conformations of diarylethene.
• The switch of the photochromism of the molecule can be operated by pH.
• The fluorescence of the molecule can be switched by proton and light irradiation.
• The switch of the fluorescence and photochromic properties is in a synergistic mode.

A rhodamine-modified diarylethene was designed and synthesised which could respond to both pH and irradiation in a synergic manner. This molecule shows neither fluorescence nor photochromism in neutral or alkaline aqueous solution (pH ≥ 7). When the pH is decreased, fluorescence of the molecule is dramatically enhanced and the photochromic reactivity is unlocked. In the pH range of 1.0–4.0, the emission intensity of the rhodamine unit in the molecule can be remotely controlled by UV (360 nm) and visible light (670 nm) irradiation. Thus the switch of the fluorescence and photochromic properties of the molecule can be synergistically operated by proton and light irradiation.

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