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Pure Appl. Chem., 2011, Vol. 83, No. 4, pp. 885-898

Published online 2011-02-23

Metal nanoparticle-enhanced radiative transitions: Giving singlet oxygen emission a boost

Rasmus Toftegaard1, Jacob Arnbjerg1, Huaiping Cong1, Hossein Agheli2, Duncan S. Sutherland3 and Peter R. Ogilby1*

1 Center for Oxygen Microscopy and Imaging (COMI), Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Århus C, Denmark
2 Applied Physics, Chalmers University of Technology, 412 96 Göteborg, Sweden
3 Interdisciplinary Nanoscience Center (iNANO), Aarhus University, Ny Munkegade 120, 8000 Århus C, Denmark

Abstract: The fabrication and use of metal nanoparticles to influence electronic transitions in a given molecule is of growing interest; there is much to be gained by developing and exploiting methods to enhance weak optical signals. Singlet molecular oxygen, O2(a1g), which is an important intermediate in many oxidation reactions, particularly in biological systems, is ideally monitored by the 1275-nm O2(a1g) → O2(X3Σg) phosphorescent transition. Unfortunately, the latter is highly forbidden and, as such, often presents a severe limitation in the application of this optical probe. In this paper, we describe how this weak phosphorescent transition can be enhanced by using localized surface plasmons (LSPs) from specially engineered gold nanostructures. In an attempt to elucidate the mechanism of this process, data were recorded from samples in which we decoupled the component of the plasmon resonance that absorbs incident light from the component that scatters incident light. We find that the latter appears to be the feature of significance in the process through which singlet oxygen phosphorescence is enhanced. In this work, we also illustrate how the singlet oxygen system provides an ideal model for a general study of metal-enhanced radiative rate constants.