Insights into the Mechanism of Enhanced Rhodamine 6G Dimer Fluorescence in Mesoscopic Pluronic-Silica Matrixes

Comparative study of the spectroscopic properties of Rhodamine 6G dimers in ethanol solutions and in mesoscopic silica-Pluronic sol gel films has been performed by means of steady state and transient absorption and fluorescence methods. The dimers act as fluorescence quenchers in solutions, while their fluorescence yield is about 36 times higher in the mesoscopic films where they dominate in the fluorescence spectra. The difference is caused by about 6 times slower nonradiative excited state decay and about 6 times stronger oscillator strength of the fluorescence transition of the dimers in the films in comparison with solutions. We demonstrate that the dimer fluorescence originates from the oblique sandwich-type dimers both in solutions and in mesoscopic films. We suggest that the higher fluorescence yield of the dimers in the mesoscopic Ems is mainly caused by the stronger deviation from the planar geometrical arrangement of the sandwich-type dimer, thus causing opening of the forbidden low energy excitonic transition.