General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract: A molecular square with dimensions of about 4 nm, incorporating sixteen pyrene chromophores attached to four ditopic bay-functionalized perylene bisimide chromophores, has been synthesized by coordination to four Pt(II) phosphine corner units and fully characterized via NMR spectroscopy and ESI-FTICR mass spectrometry. Steady-state and time-resolved emission as well as femtosecond transient absorption studies reveal the presence of a highly efficient (>90%) and fast photoinduced energy transfer (k en ≈ 5.0 × 10 9 s -1 ) from the pyrene to the perylene bisimide chromophores and a very fast and efficient electron transfer (>94%, ket ≈ 5 × 10 11 up to 43 × 10 11 s -1 ). Spectrotemporal parametrization indicates upper excited-state electron-transfer processes, various energy and electron-transfer pathways, and chromophoric heterogeneity. Temperature-dependent time-resolved emission spectroscopy has shown that the acceptor emission lifetime increases with decreasing temperature from which an electron-transfer barrier is obtained. The extremely fast electron-transfer processes (substantially faster and more efficient than in the free ligand) that are normally only observed in solid materials, together with the closely packed structure of 20 chromophoric units, indicate that we can consider the molecular square as a monodisperse nanoaggregate: a molecularly defined ensemble of chromophores that partly behaves like a solid material.

The synthesis and photophysical properties of a system consisting of a bay-functionalized perylene bisimide, containing four appended pyrene and two coordinating pyridine units, and its reference system are described. A complete study of their photophysical properties was obtained using UV-vis absorption, steady state and time-resolved emission, and femtosecond transient absorption. Analysis of the data, obtained from timeresolved emission and femtosecond transient absorption spectroscopy, showed the presence of both photoinduced electron and energy transfer processes. A high yield (>90%) and fast photoinduced energy transfer (k en ≈ 6.2 × 10 9 s -1 ) is followed by efficient electron transfer (70%, k et ≈ 6.6 × 10 9 s -1 ) from the pyrene units to the perylene bisimide moiety. The energy donor-acceptor distance, R ) 8.6 Å, is calculated from the experimental energy transfer rate using Fo ¨rster theory. Temperature-dependent time-resolved emission spectroscopy showed an increase of the acceptor emission lifetime with decreasing temperature. It also indicates the presence of different conformations because two different electron transfer barriers (0.08 and 0.42 eV) were found. These barrier values were corroborated by a theoretical analysis of the energetics of the process using Marcus theory, indicating average donor-acceptor distances of 4.5 Å (room temperature) to 11 Å (at low T).

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The immobilization on a semiconductor surface of a bis(indolyl)maleimide functionalized with two carboxylic acid groups by alkylation of the indole nitrogen atoms is presented and its synthesis is described. The compound, 3,4-bis[1-(carboxymethyl)-3-indolyl]-1H-pyrrole-2,5-dione is strongly colored and emissive and the imide part can coordinate an oxidizable substrate. Its absorption and emission spectra on TiO 2 are substantially changed as compared to the spectra obtained in neat acetonitrile, indicating surface bonding through the carboxy groups. The quenching of the fluorescence of the sensitizer by the TiO 2 surface is almost complete, reflecting the high degree of association between the TiO 2 and the dye, fast charge injection and good electronic coupling between the sensitizer and the semiconductor.