A bromonaphthalene-labeled poly(acrylic acid), BNPAA, was synthesized and found to be phosphorescent in solution at room temperature. The phosphorescence of the polymer was employed to investigate (1) the influence of pH on the conformation of the polymer in aqueous solutions, (2) the interactions of BNPAA with complementary polymers [poly(1-vinyl-2-pyrrolidinone) and poly(ethylene oxide)], and (3) conformations of the polymer adsorbed on a solid-liquid interface. The phosphorescence lifetimes of BNPAA provide a probe of changes in polymer conformations that result from inter- and intrapolymer interactions. The results suggest an unusual pH dependence for BNPAA conformations in dilute solutions; e.g., significant breaks in the lifetime/pH profile are found at pH 4 and Ph 10. These unexpected results were confirmed by the observation of the same two breaks at pH 4 and pH 10 with the use of two independent photoluminescence probes, a pyrene-labeled poly(acrylic acid), PyPAA, and a ruthenium complex, Ru(byp)3(2+). The two breaks in the conformation/pH profile are explained in terms of combination of hydrogen bonding and a hydrophobic substituent effect at low pH and charge screening at high pH. Phosphorescence lifetime measurements are also used to probe the interactions of the BNPAA with complementary macromolecules such as poly(1-vinyl-2-pyrrolidinone) and poly(ethylene oxide) and with a solid alumina surface. Finally, the interaction of BNPAA with a low molecular weight substance, the cationic surfactant dodecyltrimethylammonium bromide, was also investigated by employing the phosphorescent probe.