1. School of Physics and the Collaborative Optical Spectroscopy, Micromanipulation and Imaging Centre (COSMIC), The University of Edinburgh, King's Buildings, Edinburgh EH9 3JZ, U.K., School of Chemistry, The University of Edinburgh, King's Buildings, Edinburgh EH9 3JJ, U.K., and Institute of Biophysics, Academy of Sciences of the Czech Republic, v.i.i. Kralovopolska 135, CZ-61265 Brno, Czech Republic