Thermochromic phase transition of merocyanine J-aggregate monolayer at the air–water interface

The thermochromic phase transitions of the merocyanine J-aggregate monolayers on the binary counter-ion subphases containing a pair of Mg2+ and Cd2+ (Mg2+/Cd2+ subphase) or that of Zn2+ and Cd2+ (Zn2+/Cd2+ subphase) were investigated by the visible reflection spectroscopy. The temperature of the subphase was controlled between 40 °C and a freezing temperature of the aqueous subphases. In addition to the phases of the J-band at 595 and 618 nm, a new phase of the J-band at 614 nm was found at the temperatures below 10 °C for both subphases. Although one of the ion species in the binary counter-ion subphase is different, the transition behaviors on the Mg2+/Cd2+ and Zn2+/Cd2+ subphases were almost the same, suggesting that not the atomic number but the hydrated ionic radius influences the phase transition of the merocyanine J-aggregates.