Local properties of adsorption sites probed by the emission of fluorophores of different size and shape

The photophysics of aromatic amines, having a polar excited state, adsorbed on silica is discussed based on the results obtained by stationary and time-resolved fluorescence experiments. The stationary results suggest a correlation between the molecular shape and size and the effective polarity of the adsorption site. Time-resolved fluorescence emission experiments carried out at different emission wavelengths indicate non-exponential fluorescence decays of the adsorbed molecules. These decays could be analysed globally assuming a Gaussian distribution of decay rates. Using the standard deviation of the decay rate as a measure of the width of the distribution of the local properties of the adsorption sites, these data substantiate the interpretation of the stationary fluorescence experiments.