Anthracene photophysical data

The experimental and simulation results presented here indicate that the system viscosity has an important effect on the overall rate of the photosensitization of diary liodonium salts by anthracene. These studies reveal that as the viscosity of the solvent is increased from 1 to 1000 cP, the overall rate of the photosensitization reaction decreases by an order of magnitude. This decrease in reaction rate is qualitatively explained using the Smoluchowski-Stokes-Einstein model for the rate constants of the bimolecular, diffusion-controlled elementary reactions in the numerical solution of the kinetic photophysical equations. A more quantitative fit between the experimental data and the simulation results was obtained by scaling the bimolecular rate constants by rj"07 rather than the rf1 as suggested by the Smoluchowski-Stokes-Einstein analysis. These simulation results provide a semi-empirical correlation which may be used to estimate the effective photosensitization rate constant for viscosities ranging from 1 to 1000 cP. 

Shifting our attention to the fluorophore, we consider anthracene derivatives because of our prior experience with them [18] and (more importantly) because of the wealth of data available on them in both the electrochemical and photophysical spheres. Even at an intuitive level, anthracenes are a good starting point because such rigid, well-delocalized systems are usually efficient fluorophores [32]. It is also important that the benzocrown ether receptor is transparent to the communication wavelengths of the fluorophore in excitation and in emission. Anthracene derivatives satisfy this criterion very well in this instance. Further progress can be made via three avenues and the most general path is explored first. 

Experimental errors within 5" except for the anthracene-Cl" system (errors within 10%). Data taken from S. Wawzonek and H. A. Laitinen, J. Am. Cliem. Soc.. 1942. 64. 2365. Ref. 215. Data taken from J. B. Birks Photophysics of Aromatic Molecules . Wiley-Interscience. London. 1970. Data taken from I. Berlman. Handbook of Fluorescence Spectra of Aromatic Molecules. Academic Press, New York, 1965. Data taken from M. J. Blandamer and M. Fox Cliem. Rev.. 1970. 70. 59. V. M. Berdnikov and N. M. Bazhin. Russ. J. Pliys. Chem.. 1970, 44. 395. Calculated values from the equation (ccts) = 1.35 (X /X ) + 3.55 in eV units. Vs. the standard hydrogen electrode... 

---