Cleaving colloidal chains by photoinduced electron transfer on the particle surface

Fluorescent silica or polystyrene latex particles are commercially available and are widely used in soft matter research. Recently, we demonstrated the preparation of chains of fluorescent colloids held together by a crosslinked mesh of an amine containing polymer, polyethyeneimine (Faraday Discussions, 2016, 186, 61; ACS Nano, 2017, 11, 10025). However, on prolonged excitation of the fluorescent dye, the collaidal chains were cleaved. Here, we demonstrate that free radical reactions can be initiated by irradiation of fluorescent colloidal particles adsorbed with PEI. Free radical ions generated at the surface can cleave a cross-linked polymer mesh that holds together colloidal assemblies or can polymerize acrylic acid monomer at the particle surface (viz. bond breaking or bond formation). Proximity of polymeric amine groups allows photo-induced electron transfer from excited dye molecules, to form free radical ions. Formation of free radical ions is not a function of the size of the colloid, neither is it restricted to a specific fluorophore. Fluorophores with redox potentials that allow photo-induced electron transfer with amine groups show formation of free radical ions.