Thermally Stable Merocyanine Form of Photochromic Spiropyran with Aluminum Ion as a Reversible Photo-driven Sensor in Aqueous Solution

A reversible photo-driven sensor for aluminum ions based on photochromicspiropyran was reported with rapid response time. The detection of aluminum wasperformed via the chelation of aluminum ions with the merocyanine form (MC) ofphotochromic spiropyran. 1H NMR studies confirmed the conversation from the MC forminto the Al3+ -MC form. Addition of aluminum ions to the spiropyran (SP) in a MeCN/H2Omixture results in obvious color changes with a loss in absorbance at 539 nm and anenhancement in absorbance at about 420 nm after irradiation at 365 nm. The metal chelationcomplex (Al3+ -MC) can also be converted into the original SP form by irradiation withvisible light. Aluminum ions can be detected down to 0.5 μM levels in a fast response ofless than 5 seconds with no interference from other ionic species.