Photoluminescence quenching effects of surface-modified gold nanoparticles on side-chain polymers containing pyridyl H-acceptors with various lateral polarities

In this study, we used photoluminescence (PL) quenching and transmission electron microscopy (TEM) to study the morphological behavior of hydrogen-bonded (H-bonded) supramolecular assemblies of luminescent H-acceptor polymers and H-donor gold nanoparticles (Au NPs). In fluorescence titration experiments, the lateral Me and MeO substituents on the fluorescent H-acceptor side-chain polymers PBOT1–PBOT3 and PBT1–PBT3 exhibited different electron-donating capabilities, thereby inducing different degrees of H-bonding and dipole–dipole interactions, as evidenced by effective fluorescence quenching upon the addition of surface-modified Au NPs bearing acid and acid-free surfactants (AuSCOOH and AuSC10, respectively). Among all of our tested nanocomposites, the highest Stern–Volmer quenching constant (K_SV) was that obtained from the assembly of AuSCOOH with the homopolymer PBOT1. In addition, we developed fittable exponential equations to predict the values of K_SV of other fluorescent polymers (containing various molar ratios of pyridyl conjugated units) when titrated with these NP quenchers. The morphologies observed in the TEM images confirmed that fluorescence quenching resulted from the self-assembly of the supramolecular nanocomposites, mediated by H-bonds between the fluorescent H-acceptors of the polymers and the H-donors of the Au NPs presenting acid-modified surfactants.