Mapping Long-Lived Dark States in Copper Porphyrin Nanostructures

作者：Hartmann Hannes; Barke Ingo; Friedrich Aleksej; Ploetz Per Arno; Bokareva Olga S; Bahrami Mohammadreza; Oldenburg Kevin; Elemans Johannes A A W; Irsig Robert; Meiwes Broer Karl Heinz; Kuehn Oliver; Lochbrunner Stefan; Speller Sylvia

来源：Journal of Physical Chemistry C, 2016, 120(30): 16977-16984.

DOI：10.1021/acs.jpcc.6b01279

Long-lived excited states in molecular aggregates are a promising route for efficient energy transfer with potential applications in optoelectronic devices. Spatially resolved optical detection of these states is challenging due to a critical trade-off between sufficiently high photon emission rates and negligible contribution of the luminescence channel to the total lifetime. Here, we report on selective mapping of excited states in copper tetraundecylporphyrin (CuTUP) assemblies on graphite (HOPG) using two-photon photoemission electron microscopy. While the photoemission electron microscopy (PEEM) data are consistent with time-resolved luminescence measurements on a nanosecond time scale, additional long-lived states with lifetimes in the microsecond range are found with nondetectable emission of photons. These,dark states serve as initial states in a subsequent photoemission process, giving rise to a high yield and, pronounced lateral contrast. In combination with long-range corrected density functional theory (DFT) we analyze the energetics and nature of contributing states. Our study underlines the versatility and specificity of excitation nanoscopy by PEEM enabling high spatial resolution beyond the wavelength limit.

• 出版日期2016-8-4