Negative photochromism of a blue cyanine dye.

We found a novel blue cyanine dye that exhibits negative photochromism. Upon photoexcitation of the dye solution, the blue colour visibly disappeared, and after several hours the absorbance of the solution recovered completely, indicating that the dye has high stability.

Estimation of quantum yields of weak fluorescence from eosin Y dimers formed in aqueous solutions.

We studied the weak fluorescence from the dimer of eosin Y (EY) in aqueous solutions. We used a newly developed ultrathin optical cell with a thickness ranging from of the order of microns to several hundreds of microns to successfully measure the fluorescence spectra of highly concentrated aqueous solutions of EY without artifacts caused by the reabsorption of fluorescence. The spectra we obtained were similar to the fluorescence spectrum of the EY monomer; almost no fluorescence was observed from the EY dimer. By a careful comparison of the spectra of solutions at low and high concentrations of EY, we succeeded in extracting the fluorescence spectrum of the EY dimer. The fluorescence quantum yield of the EY dimer was estimated to be 0.005.