Self-assembly and photopolymerization of a novel quaternary-ammonium functionalized diacetylene on noble metal nanoparticles: A comparative study

Highlights: • Ag/Au nanoparticles coated with the cationic diacetylene DAAMM are prepared. • Photopolymerization of chemisorbed DAAMM occurs in red and blue form simultaneously. • Polymerized nanohybrids have bilayered structure and are stable for months in water. • DAAMM assembly and photopolimerization are more effective on Au nanoparticles. • Unlike PCDA, optimal packing of DAAMM cannot be achieved on Ag and Au nanoparticles. Stable hydrosols of gold and silver nanoparticles coated with the quaternary-ammonium group endowed diacetylene DAAMM (N,N,N-trimethyl-3-(pentacosa-10,12-diynamido)propan-1-ammonium) were obtained through a ligand-exchange reaction leaving the morphology of the pristine cores unmodified. Photopolymerization of the chemisorbed diacetylene shell occurred in both red and blue phases thanks to the presence of internal, H-bondable amide functions in the monomer chain, which are supposed to help the formation of a packed bilayer on the metal surfaces. Multidisciplinary characterization of the polymerized samples, including spectroscopic, morphological and thermal techniques, highlighted that differences occur in the polymerization process on gold and silver nanoparticles under different experimental conditions, suggesting a higher affinity of the trimethylammonium headgroup for gold substrates in acidic media. With respect to the extensively investigated PCDA (pentacosa-10,12-diynoic acid), DAAMM showed reduced capability of photogenerating thick polymer shells, especially in the more delocalized blue form, probably because of the inefficiency of the cationic monomer to form the multi-bilayered architecture typical of the highly-performing, carboxyl-terminated diacetylene. On the other end, the inner cross-linked structure gives to poly(DAAMM)-coated nanohybrids increased stability in water with respect to self-assembled counterparts deriving from saturated cationic surfactants, making them a promising sensing platform for rapid and cost effective assays of real samples.