1. Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland, Laboratoire de Photophysique Moleculaire du CNRS, Batiment 213, Universite de Paris-Sud, 91405 Orsay, France, and Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka44/52, 01-224 Warsaw, Poland