1. Laboratory for Photonics and Interfaces, Institute of Chemical Sciences and Engineering, Swiss Federal Institute of Technology, CH-1015 Lausanne, Switzerland, Nanomaterials Research Centre and MacDiarmid Institute for Advanced Materials and Nanotechnology, Massey University, Palmerston North, New Zealand, and MacDiarmid Institute for Advanced Materials and Nanotechnology, Chemistry Department, University of Otago, Dunedin, New Zealand