Electrogenerated chemiluminescence. 74. Photophysical, electrochemical, and electrogenerated chemiluminescent studies of selected nonplanar pyrenophanes

We report here the photophysical, electrochemical, and electrogenerated chemiluminescent studies of four new pyrenophanes. Comparison with the cyclic voltammogram obtained using the planar parent compound, pyrene, showed these bent-pyrene-containing cyclophanes have a shift in the thermodynamic reduction potentials to more negative values. AM1 semiempirical calculations support such findings in which the LUMO energy increased with the degree of nonplanarity. The HOMO energy, however, remained essentially unchanged for all the compounds in this study. The nonplanarity in these compounds resulted in a substantial decrease in fluorescence quantum yield as well as a slight red shift in both the absorption and emission spectra. In addition, unlike pyrene, no excimer emission was evident in the fluorescence spectra even at concentrations as high as 1 mM. However, the ECL spectra of all four pyrenophanes, produced by generating the anion radical in the presence of benzoyl peroxide as a coreactant, showed broad excimer-like emission in addition to the monomer emission observed at shorter wavelengths.