| Abstract
| - A molecular square with dimensions of about 4 nm, incorporating sixteen pyrene chromophoresattached to four ditopic bay-functionalized perylene bisimide chromophores, has been synthesized bycoordination to four Pt(II) phosphine corner units and fully characterized via NMR spectroscopy andESI-FTICR mass spectrometry. Steady-state and time-resolved emission as well as femtosecond transientabsorption studies reveal the presence of a highly efficient (>90%) and fast photoinduced energy transfer(ken ≈ 5.0 × 109 s-1) from the pyrene to the perylene bisimide chromophores and a very fast and efficientelectron transfer (>94%, ket ≈ 5 × 1011 up to 43 × 1011 s-1). Spectrotemporal parametrization indicatesupper excited-state electron-transfer processes, various energy and electron-transfer pathways, andchromophoric heterogeneity. Temperature-dependent time-resolved emission spectroscopy has shown thatthe acceptor emission lifetime increases with decreasing temperature from which an electron-transfer barrieris obtained. The extremely fast electron-transfer processes (substantially faster and more efficient than inthe free ligand) that are normally only observed in solid materials, together with the closely packed structureof 20 chromophoric units, indicate that we can consider the molecular square as a monodispersenanoaggregate: a molecularly defined ensemble of chromophores that partly behaves like a solid material.
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