Waterchromism of protonated photomerocyanine dye

The red protonated photomerocyanine (PMCH) of spirooxazine (SPO) experiences a stepwise color modulation from red to purple and ultimately blue upon gradual addition of water. Both UV–vis absorption spectra and thermal bleaching kinetics indicate that the blue solution differs from the open form of SPO, i.e., photomerocyanine (PMC), and computer assisted simulations show that the blue solution is a complex composed of one PMCH and two water molecules, which are connected through hydrogen bonds. Thus, water has a characteristic effect on PMCH, and this phenomenon is proposed as waterchromism.