Comparative study of the optical behavior of a porphyrin encapsulated in sol-gel silica coatings and in solution as a function of pH

• Porphyrin-doped silica coatings were prepared by sol-gel.
• Films optical properties were studied and compared to the behavior of the molecule in solution.
• A quasi-linear behavior throughout the pH range studied was found.
• Luminescent emission peak and molar absorptivity were maximum at slightly lower wavelength than molecule in solution.

We report a comparative optical spectral study as a function of pH on a porphyrin encapsulated in a sol-gel matrix and in methanol solution. Its response has been discussed in terms of pH-sensitivity as a function of the coatings thickness. Comparison with the behavior of such porphyrin in methanol solution is also included.Optical properties of the porphyrin doped coatings show a quasi linear behavior throughout the pH range studied. Luminescent emission of doped coatings has its maximum peak at a slightly lower wavelength compared with the response in liquid medium (methanol solution), while in the excitation spectra no clear tendency was observed for different pH. Coatings doped with 1 wt% porphyrin fulfill Lambert-Beer law, although the molar absorptivity of the encapsulated porphyrin in the coatings is slightly lower than in methanol solution.

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