A new modular concept for the self-assembly of electron donor-acceptor complexes is presented that ensures (i) fine-tuning the strength of the complexation, (ii) controlling the electronic coupling to impact electron and energy transfer processes, and (iii) high solubility of the corresponding hybrid architectures. This task has been realized through developing a series of porphyrin-fullerene donor-acceptor systems held together by a Hamilton-receptor-based hydrogen-bonding motif. In this context, novel libraries of C60 monoadducts (1) containing cyanuric acid side chains and of tetraphenylporphyrin derivatives (2) involving the complementary Hamilton-receptor unit were synthesized. The association constants of the corresponding 1:1 complexes (1.2) connected by six hydrogen bonds were determined complementary by NMR and fluorescence assays. Their strength, which was found to be in the range between 3.7 x 10(3) and 7.9 x 10(5) M-1, depends on the nature of the spacers, namely, hexylene versus propylene chains. Finally, transient absorption studies revealed photoinduced electron transfer from ZnP to C60 in the corresponding 1.2 complexes, which generate radical ion pair states that are persistent well beyond the ns time scale. In the case of the analogous SnP complexes, energy instead of electron transfer was observed. This is due to the shift of oxidation potential caused by presence of Sn in the oxidation state of +4.
Self-assembled structures are widespread in nature and are a key feature of many biological small-molecule recognition motifs. Not surprisingly, therefore, considerable effort has been devoted to developing synthetic self-assembled receptor systems, multicomponent molecular hosts that are able to[*] Dr.
The imidoylamidinate platinum(II) compounds [Pt{NH=C(R)NC(Ph)NPh}2] (R = CH2Ph 2, p-ClC6H43, Ph 4) were prepared by the reaction of the appropriate trans-[PtCl2(RCN)2] with 4 equiv of the amidine PhC(NH)NHPh giving 2-4 and 2 equivs of the salt PhC(=NH)NHPh.HCl. We also synthesized, by the double alkylation of 4 with MeOSO2CF3, complex [Pt{NH=C(Ph)N(Me)C(Ph)=NPh}2][CF3SO3]2 (5) which models the bis-protonated form of 4. The complexes were characterized by 1H, 13C NMR, and IR spectroscopies, FAB-MS and by C, H, N elemental analysis. The X-ray crystallography of 4.2CH2Cl2 enables the confirmation of the square planar coordination geometry of the metal center with almost planar imidoylamidine ligands, while in 5.2CHCl3 the planarity of the metallacycles is lost and and the central N atom is sp3-hybridized. The imidoylamidinate complexes represent a new family of Pt(II)-based luminescent complexes and they are emissive at room temperature both in solution and in the solid state, with an emission quantum yield ranging from 3.7 x 10(-4) to 6.2 x 10(-2) in methanol solution; the emission intensity is pH-dependent, being quenched at low pH. UV-visible and luminescence spectroscopies indicate that the lowest excited state of these compounds is 3MLCT or 3IL with significant MLCT character, with emission lifetimes of a few micros. A blue shift of both the absorption and emission with increasing solvent polarity and with decreasing pi-electron withdrawing properties of the ligand substituent was observed.
In this work, we describe the insertion of a water-soluble bisadduct fulleropyrrolidine derivative into the interlayer space of three layered smectite clays. The composites were characterized by a combination of powder X-ray diffraction, transmission electron microscopy, X-ray photoemission and FTIR spectroscopies, and laser flash photolysis measurements. The experiments, complemented by computer simulations, give insight into the formation process, structural details, and properties of the fullerene/clay nanocomposites. The reported composite materials constitute a new hybrid system, where C(60) differs from its crystals or its solutions, and open new perspectives for the design and construction of novel C(60)-based organic/clay hybrid materials.
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