Mapping Long-Lived Dark States in Copper Porphyrin Nanostructures

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• 作者：Hannes Hartmann ; Ingo Barke ; Aleksej Friedrich ; Per-Arno Plötz ; Olga S. Bokareva ; Mohammadreza Bahrami ; Kevin Oldenburg ; Johannes A. A. W. Elemans ; Robert Irsig ; Karl-Heinz Meiwes-Broer ; Oliver Kühn ; Stefan Lochbrunner ; Sylvia Speller
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：August 4, 2016
• 年：2016
• 卷：120
• 期：30
• 页码：16977-16984
• 全文大小：429K
• 年卷期：0
• ISSN：1932-7455

文摘

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.