Anthracene based photo-tunable polymers with excimer emission

Abstract

The aggregation properties of a diblock and a triblock copolymer in the aqueous phase has been investigated by photophysical and microscopy methods. Both copolymers possess photoresponsive hydrophobic poly(9-anthrylmethyl methacrylate) (PAN) block and hydrophilic polyethylene oxide (PEO) block whereas the triblock copolymer have an additional polystyrene (PSt) block at the middle. The amphiphilic copolymers, PAN-b-PEO and PAN-b-PSt-b-PEO, were synthesized by atom transfer radical polymerization (ATRP) method. Self-assembly of these individual copolymers in water leads to the formation of uniform spherical supramolecular assemblies. The morphology of the resultant spheres was disturbed by the illumination of the turbid aqueous solutions with 360 nm UV light accomplished by the photosolvolysis of the anthracenylmethyl ester. This irreversible photodissociation virtually transforms the amphiphilic diblock copolymer to a double hydrophilic block copolymer whereas the triblock copolymer because of its central PSt block was transformed into a bolaamphiphile. Complete micellar dissociation obtained in the case of diblock was not observed in the case of vesicular aggregates of the triblock copolymer. We also found that compared to the completely dissolved state, aggregation resulted in the pronounced excimer emission of the anthracene copolymers.