Trapping of Rhodamine 6G excitation energy on cellulose microparticles

Abstract

Rhodamine 6G (R6G) was adsorbed on cellulose microparticles and fluorescence quantum yields and decays were measured as a function of dye loading. Though no spectroscopic evidence of dye aggregation was found, a noticeable decrease of quantum yield--after correction for reabsorption and reemission of fluorescence--and shortening of decays were observed at the highest loadings. These effects were attributed to the dissipation of the excitation energy by traps constituted by R6G pairs, leading to static and dynamic quenching produced by direct absorption of traps and non-radiative energy transfer from monomers, respectively. Regarding the nature of traps, two extreme approaches were considered: (a) equilibrium between monomers slightly interacting in the ground state and (b) randomly distributed monomers located below a critical distance (statistical traps). Both approaches accounted quantitatively for the observed facts. The effect of energy migration was evaluated through computational simulations. As the concentration of traps could only be indirectly inferred, in some experiments an external energy transfer quencher, Methylene Blue, was coadsorbed and the results were compared with those obtained with pure R6G.

Eosin Y Triplet State as a Probe of Spatial Heterogeneity in Microcrystalline Cellulose

“…At the highest loadings, concentration quenching is observed, although the aggregation tendency should be small as pointed out above. Similar results obtained for rhodamine 6G on cellulose, a system for which no aggregation could be detected spectroscopically, were attributed to excitation energy transfer and trapping (10).…”

“…Small amounts of water, however, strongly affect the excited state behavior of the adsorbed molecule (21). Some studies of xanthene and other dyes adsorbed on microcrystalline cellulose, such as rhodamine 6G, rhodamine 101, auramine O, rose bengal, etc., have been reported by us (10,(22)(23)(24).…”

Click-based thiol-ene photografting of COOH groups to SiO2 nanoparticles: Strategies comparison

“…shows the fluorescence spectrum of the PhG-SiO2, after being modified with aminofluorescein according to Scheme 3, with a maximum emission at 517 nm. Similar spectra have been obtained for the other fluorescent derivatives from the carboxylic NPs; small differences in peak emission (5 nm) respect to the free dye can be attributed to the change of photophysical parameters and have been observed in surface immobilized dyes (Figure ESI 5(a)) [48,49]. When the coupling reagents EDC and NHS are not present there is no fluorescence signal, pointing that the immobilization of fluorescein does not take place and we can rule out adsorption of the dye on the SiO2 surface.…”

Photophysics of Xanthene Dyes at High Concentrations in Solid Environments: Charge Transfer Assisted Triplet Formation

“…Results concerning the formulation of photoactive materials obtained by our research group during the last years show that concentration quenching (CQ) precludes the achievement of efficient materials at not quite high dye concentrations. In particular, for xanthenes and similar dyes, we demonstrated that, even in the absence of spectroscopically detectable aggregation, dye pairs with molecules separated by less than 1.5 nm behave as virtual traps for the excitation energy (1). Beddard and Porter concluded long ago that, to prevent trap formation by orbital overlap, the minimum distance between chlorophyll molecules should be 1 nm when averaged over all orientations at random (2).…”