PHOTOPHYSICS OF SUBSTITUTED 1,8-NAPHTHALIMIDES BOUND TO A POLY(ALLYLAMINE) POLYMER

Poly(allylamine) has been modified by imidization of 0.02-0.08 mole fraction of available amino groups with 1,8-naphthalic anhydride or the corresponding 4-bromo and 4-sulfo derivatives. These latter chromophores have a strong absorption in the visible region (ca. 450 nm) and a high fluorescence quantum yield. The photophysical properties of the polymer-bound chromophores have been compared with model compounds. For the 4-substituted chromophores the fluorescence spectra of the polymer-bound species are similar to the model compounds but the fluorescence yield is decreased, and the multiexponential fluorescence decay implies a heterogeneous environment. The unsubstituted 1,8-naphthalimide exhibits excimer fluorescence when polymer-bound, even at 0.01 mole fraction loading. These results imply a strong tendency for the chromophores to aggregate, presumably intracoil. These photophysical properties are a function of pH and/or ionic strength, which affects the coil expansion. Fluorescence quenching was also studied as a function of pH and/or ionic strength, in an effort to elucidate the accessibility of the polymer-bound chromophores.