Rhodamine Fluorescent Dimers Adsorbed on the Porous Surface of Silica Gels

Abstract

Rhodamine 6G (R6G)-doped silica gels were prepared through the sol−gel process using dye concentrations ranging from 4.00 × 10-6 to 6.40 × 10-4 M. The adsorption of the R6G on the porous surface of the silica gels determined the formation of R6G fluorescent J-dimers as concentration increased, in concordance with the behavior reported for other xanthene molecules as rhodamine B (RB) and rhodamine 110 (R110) also doped in silica gels. The photophysical study of the R6G fluorescent dimers doped in silica gels was done through the recording of the excitation and emission fluorescence spectra as well as the measurement of the lifetime values. The exciton theory was used for the elucidation of the adsorption angle (θ), the angle between the monomer units (α), and the separation distance between the molecules (R) of the R6G fluorescent dimers. The angle between the monomer units (α) and the separation distance between the molecules (R) were also determined for RB and R110 fluorescent dimers doped in silica gels.

Sol–gel prepared AlPO4 with incorporating Rhodamine 6G

“…6) shows an obvious red shift of the main band from 540 nm to 562 nm with increasing the RH6G concentration from Gel-a to Gel-d. This is a general observation in solid-state matrices and is attributed to the increase of angle of J-dimer with the increase of RH6G dye concentration [18]. On the other hand, the energy loss due to the interactions among molecule increase as the molecular amount increases.…”

Fluorescence properties of dye doped mesoporous silica

“…All the emission measurements were carried out in the ''front face mode'' by collecting the PL signal in the backward direction in order to minimize the re-absorption effects, [47] as reported for comparable systems. [8][9][10][11][12][13][14] The spectra were corrected for the optical transfer function of the adopted measurement system. Absorbance measurements were carried out by exciting the samples with a 100 W tungsten lamp and recording the transmitted signal with the photonic multichannel analyzer (Hamamatsu PMA-11, spectral resolution 1 nm).…”

“…Within the porous matrix it is possible to introduce a large content of organic molecules of interest: this concentration effect is related to the huge specific surface of the porous matrix and is the basis of the numerous applications of the nanomaterials. In photonics this characteristic was the subject of researches aimed to produce organic-inorganic hybrids to be exploited as active medium in solid state dye lasers [8][9][10][11][12][13][14][15][16][17]. In the biotechnology field the concentration effect is the functioning principle of controlled drug delivery systems and for the engineering of fluorescent nanostructures for cell imaging.…”

“…Another problematic issue is the determination of the concentration limit for organic molecules that can be introduced within the porous matrix. The concentration effect was studied concerning the formation of aggregates, mainly for dye molecules of the Xanthene class adsorbed on transparent inorganic matrices [10][11][12][13][14][15]. Depending on the dye concentration it is indeed possible to detect the formation of aggregates due to the electrostatic interaction of isolated molecules (monomers) and the host polar surface.…”

“…It was shown that there is a concentration threshold above which the formation of aggregates causes the presence of non-radiative dis-excitation patterns and the decrease of the fluorescence efficiency. To achieve mesoporous nanostructures with large emission efficiency is a goal still open, in particular for applications in photonics, such as solid state dye laser, and in the biomedicine field to achieve fluorescent nanoprobe for cell imaging [10][11][12][13][14][15][29][30][31][32][33][34][35]. In this respect in the last years new synthesis procedures were proposed to solve the exposed drawbacks to achieve ultrabright nanostructures by sealing the matrix by means of a templated procedure, by proper functionalization.…”