Luminescence characterization of a novel, hydrophobically modified and heavy atom-functionalized, water-soluble polymer

A hydrophobically modified water-soluble polymer, based upon acrylic acid a nd styryl derivatives, was synthesized. A proportion (ca. 75 mol%) of the s tyryl residues in the copolymer contain a bromine substituent as a "heavy-a tom" functionality It has been shown that room-temperature phosphorescence (RTP) can be induced in an acenaphthylene (ACE) label, covalently bound to the polymer chain, through intramacromolecular interactions in dilute solut ions of the copolymer. This is the first instance in which RTP has been gen erated in either label or solubilized guest, in such a fashion. The conform ational behavior of the functionalized copolymer, BrSTY/STY/AA, has been st udied using RTP, fluorescence lifetime, and time-resolved anisotropy measur ements and compared to that of both its unbrominated, styrene-modified anal ogue, STY/AA, and poly(acrylic acid) PAA itself The conformation transition which accompanies conversion of each polyacid into the corresponding fully neutralized polysalt is much more dramatic in either hydrophobically modif ied species than in poly(acrylic acid). Intramacromolecular aggregation lea ding to the creation of hydrophobic domains within the coils of the macromo lecules is enhanced at a low pH and severely impedes segmental motion in th e two styrene-modified polyacids. The effect is greater in the bromine-cont aining polymer, which suggests that more densely packed domains are formed in this species than in STY/AA. In addition to altering the magnitude of th e effect that neutralization has upon the molecular dynamics of the polyaci d in aqueous media, hydrophobic modification raises the pH range over which the change in conformational behavior of the macromolecule is apparent.