Fluorescence and Triplet Quantum Yields of Arenes on Surfaces

Abstract

The photophysics of pyrene, perylene, coronene, and several other polyaromatic adsorbates on silica gel and related oxide surfaces have been examined using their excited singlet and triplet states. It is found that the fluorescence and triplet quantum yields for the arenes are lower on silica gel compared to simple solution. This is related to the adsorption of the molecules on SiO2 sites where charge-transfer (CT) complexes are formed. The CT complex is identified by its spectral absorption and emission, which are red-shifted with respect to pyrene, and by a much shorter lifetime of 20 ns compared to greater than 100 ns for pyrene. The extent of the CT state can be reduced by addition of polar coadsorbates such as nitromethane. The latter adsorb strongly at the active surface sites and replace pyrene, which then adsorbs at nonactive sites.

Quantum Yield Measurement of Fluorescent Zeolite Nanopigments

“…Diffuse reflectance measurements [22][23][24] were used to measure the quantum yield of both PDB molecules and Z-PDB nanoparticles adsorbed on the cellulose. In particular, an integrating sphere was used to measure the diffuse reflectance of microcrystalline cellulose substrates containing either fluorescent molecules (e.g., PDB) or Z-PDB nanoparticles with or without a cut-on filter in front of the detector.…”

“…Quantum Yield Measurement by a Diffuse Reflectance Technique [22][23][24]: The quantum yield of the investigated fluorophors was measured by a diffuse reflectance method [25].…”

“…The materials and their optical characterization are presented in Section 2. The diffused reflectance measurements [22][23][24][25] are discussed in Section 3, where several factors that may influence the zeolite quantum yield are investigated. Conclusions and perspectives are illustrated in Section 4.…”

Fluorescent nanopigments: Quantitative assessment of their quantum yield

“…Based on previous studies by Ruetten and Thomas 56 and Ferreira et al, 57 we developed an optical DR technique to measure the absolute quantum yield of fluorescent nanopig- ͑Color͒ Steady-state emission spectra of ͑a͒ ZL-P and ͑b͒ PMMA-L nanopigments adsorbed onto microcrystalline cellulose for increasing nanoparticle contents ͓in mg ͑nanoparticle͒/g ͑cellulose͔͒. In the insets, the spectra for the lowest and the largest nanoparticle concentrations ͑0.05-1.00 mg/g and 1.5-40 mg/g for ZL-P and PMMA-L, respectively͒ have been normalized at 600 nm ͑where self-absorption is absent: see Figs.…”

“…5,55 Our experimental method is based on the measurement of the diffuse reflectance ͑DR͒ spectra of fluorescent nanopigments adsorbed on microcrystalline cellulose substrates. In particular, we adapted the DR technique previously developed by Ruetten and Thomas 56 and Ferreira et al 57 for the measurement of the fluorescence efficiency of organic dyes to the assessment of the quantum yield of organic-inorganic and organic-organic nanopigments, for which both light scattering and self-absorption strongly affect the fluorescence emission. To this purpose, an optical bench was equipped with a standard lamp-monochromator system and a calibrated integrating sphere coupled to a photodetector, which eventually eliminates any influence of the nanoparticle emission anisotropy on the optical measurements.…”