Metal ions-triggered photo-induced fluorescence change in rhodamine B-based photo-responsive complexes

Photo-responsive materials with tunable properties by multiple stimuli have been widely used as molecular machines, molecular logic gates, optical data storages, etc. In this work, we report a rhodamine B-based photo-responsive system, whose properties could be facilely modulated by metal ions (Zn(II), Ni(II) and Hg(II)). These metal ions endow the complexes (L-Zn, L-Ni and L-Hg) with similar photochromic property but distinctly different photo-induced fluorescence change. Upon UV light irradiation, the spirolactam ring in rhodamine B moiety turned from a close form to an open form, along with enlarged conjugated structure with intense absorbance. Interestingly, fluorescence "turn off", "no change" and "turn on" responses were induced by Zn(II), Ni(II) and Hg(II) respectively upon UV light irradiation. Taking advantage of the prominently different characteristics caused by metal ions, different logic gates were designed by simply varying the inputs of metal ions and UV light. This work provided a new strategy for developing multifunctional photo-responsive materials, which were further beneficial for constructing photo-controlled logic gates with tunable performance.