Steady-State Fluorescence of Dye-Sensitized TiO₂ Xerogels and Aerogels as a Probe for Local Chromophore Aggregation

Abstract

Sol-gel synthesis has been used to disperse an emissive chromophore within a porous TiO 2 matrix, leading to xerogels and aerogels doped with tethered and unbound pyrenyl groups. Steady-state fluorescence was used to probe the interactions of neighboring pyrene groups within the gel matrix. Changes in the relative intensity of the monomer (I 1 ) emission peak as a function of chromophore concentration indicated a local interaction between included dyes for both tethered and unbound pyrene groups, likely through π stacking. Partial matrix methylation or phenylation failed to produce a significant effect on the relative intensity of the I 1 signal in either the xerogel or the aerogel. Changes in the relative intensity of excimer emission with changes in matrix composition, however, do suggest that the presence of either phenyl or methyl groups within the TiO 2 matrix impedes π stacking between pairs of tethered pyrenyl groups. Compared with strong excimer emission in the xerogels containing pyrenyl groups at relatively high concentrations, excimer formation was inhibited in the corresponding aerogels, for which BET analysis indicated a broad pore size distribution in the mesoporous range, ca. 100 Å.

Photophysical Probes for Multiple-Redox and Multiple-Excited-State Interactions in Molecular Aggregates

“…In the available space, we can only bring along a representative discussion of catalysis or photocatalysis in self-assembled monolayers (SAM), − in reactive shell–core clusters (SCC), − in functional polymers, − and in dendrimers. − These families are highlighted because each class bears structural features that could possibly accommodate multiple charges when properly functionalized. It is also important that we consider how physical dispersal of dyes in those arrays affects the excited states of fully loaded aggregates, how directionality toward a target must be included in molecular design, and what competing paths − influence the long-term stability of the whole array. We also take a quick overview of applicable devices − that are dependent on high density chromophores and efficient photoinduced electron transfer.…”

Zirconia Aerogels with High Surface Area Derived from Sols Prepared by Electrolyzing Zirconium Oxychloride Solution: Comparison of Aerogels Prepared by Freeze-Drying and Supercritical CO2(l) Extraction

“…In particular, these aerogels have attracted significant attention because of their excellent heat-insulation properties . The conventional approach to producing the aerogels is to first prepare the wet gels through the hydrolysis and condensation of alkoxide precursors and then dry the gels to remove the solvents . During this process, not only is control of hydrolysis complicated but also the required precursor is expensive.…”