Time-resolved spectroscopy of single molecules using near-field and far-field optics

Room-temperature spectra and excited state lifetimes of single molecules obtained with conventional, far-field optics are reported, for the first time. The sample was the same as that used in our previous near-field single molecule work, namely 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo (diI) dispersed in a thin film of polymethylmethacrylate. In a critical comparison of the two methods we have found that superior spatial resolution and more complete information on the orientation of the molecule are available with near-field excitation, whereas presently, excited state lifetimes can be accurately determined only under far-field illumination. In addition, greater data rates are possible with far-field excitation, without perturbing the molecule. Which method proves better will depend on the particulars of the system under investigation.