Energy and electron transfer processes in polymeric nanoparticles

Abstract

We report herein a study on photoinduced electron transfer (eT) and energy transfer (ET) processes occurring between 9-methylanthracene-acrylate (A) and N,N-dimethylaniline-acrylate (D) derivatives incorporated into polymeric nanoparticles (NP). Five types of NPs were synthesized: PAD0, PAD25, PAD75, PD25, and PD75. All NPs are composed of a crosslinked polymer matrix of methyl methacrylate and ethylene glycol dimethacrylate. In addition, PAD0, PAD25 and PAD75 contain low doping levels of A. For PAD25 and PAD75, 25% and 75% of the mole fraction of methyl methacrylate is replaced by D, respectively. PD25 and PD75 were prepared as above but without A. NPs (diameter 6-9 nm) dispersed in organic solvents were characterized based on their UV-visible absorption, emission, excitation, and excitation anisotropy spectra and time dependent absorption and emission spectroscopy techniques. The emission decay profiles of A and D were always complex. Results indicate that A senses two distinct environments in all NPs. The emission quenching of PAD0 by DMA in DCM solutions is dynamic, and it is apparent that a significant fraction of A is inaccessible to the quencher. The emission of A is efficiently quenched by the presence of D in PAD25 and PAD75. The intra-NP photoinduced eT quenching mechanism has static and dynamic components. Selective excitation of D in PAD25 and PAD75 leads to the formation of the excited state of A via a singlet-singlet ET Föster type mechanism. Results indicate that both intra-NP eT and ET processes are more efficient in PAD75 due to the reduced average D*-A separation in these NPs.