Xerogels fluorescent

Given the challenges that are associated with creating BPs that can deliver active proteins and/or diversified xerogel-based sensor platforms for chemical sensor applications, we have developed automated systems that can rapidly prepare large numbers of BP or xerogel-based materials and rapidly obtain fluorescence-based spectroscopic information from these formulations. Ultimately, these laboratory... 

Figure 8.7 Top Effect of density on the optical bandgap for aerogels prepared from naked CdSe nanopaiticles and CdSe-ZnS core-shell nanoparticles. Bottom CdSe-ZnS core-shell aerogel and xerogel monohths under normal (left) and UV (right) illumination. The native aerogel and xerogel are orange under normal hght and fluorescent green under UV stimulation.

Howell A R, Fox M A (2003) Steady-state fluorescence of dye-sensitized Ti02 xerogels and aerogels as a probe for local chromophore aggregation. J Phys Chem A 107 3300-3304. 

The fluorescence spectrum of pyrene has been very often nsed as a photophysical probe. The fluorescence spectmm shows the vibronic strnctnre, which is sensitive to the polarity of the environment (Nakajima, 1971 Kalyanasnndaram, 1977). Moreover, pyrene forms excimer due to one molecnle in the groimd state and one in the excited state for concentrated systems. Therefore, fluorescence spectra of pyrene can be expected to reveal the stmctnral changes of sol-gel silica and trapping mechanism of organic molecnles along the sol-gel-xerogel transitions... 

The intensity ratio of the third peak (384 nm) to the first peak (373 nm 0-0 band) ih/h) has been used (Matsui, 1990). Figure 20-1 shows examples of the fluorescence spectra of pyrene in the starting sol-gel solution of ethanol, water and tetraethoxysilane (TEOS) and the xerogels. It is clearly seen that the relative intensities of the vibronic... 

Figure 20-1. Fluorescence spectra, of pyrene in a TEOS-derived sol and xerogel The relative intensity of the vibronic bands (1, 3, and 5) is correlated with solvent polarity.

Figure 20-4. Monomer fluorescence ofphenyl groups in a sol and the excimer fluorescence in the xerogel after 3 months derived from 20 mol% ofPh TES 80 mol% of TEOS.

Figure 20-S. Shifts in vibrational frequencies of IR spectra and fluorescence peaks in xerogels derived from PhTES-TEOS after 3 months against mol% of PhTES.

The fluorescence level inversion of 1-naphthol from La to Lb occurred after the gelation ofTEOS, while the fluorescence spectrum of 2-naphthoI molecules during the sol-gel-xerogel transitions was almost unchanged (Fujii, 1990). Therefore, the fluorescence spectrum of 1-naphthol molecules is a useful photophysical probe. The probe was used in the sol-gel-xerogel transition systems ofmixed aluminum and silicon oxides system (Fujii, 1992, 1997). Hydrogen-bonded forms and contact ion pair forms are considered for the interaction species formed between 1-naphthol and the gel surface. 

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