Synthesis, characterization and structural analysis of complexes from 2,2':6',2''-terpyridine derivatives with transition metals.

The synthesis and structural characterization of three families of coordination complexes synthesized from 4'-phenyl-2,2':6',2''-terpyridine (8, Ph-TPY), 4'-(4-chlorophenyl)-2,2':6',2''-terpyridine (9, ClPh-TPY) and 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (10, MeOPh-TPY) ligands with the divalent metals Co2+, Fe2+, Mn2+ and Ni2+ are reported. The compounds were synthesized from a 1:2 mixture of the metal and ligand, resulting in a series of complexes with the general formula [M(R-TPY)2](ClO4)2 (where M = Co2+, Fe2+, Mn2+ and Ni2+, and R-TPY = Ph-TPY, ClPh-TPY and MeOPh-TPY). The general formula and structural and supramolecular features were determinated by single-crystal X-ray diffraction for bis(4'-phenyl-2,2':6',2''-terpyridine)nickel(II) bis(perchlorate), [Ni(C21H15N3)2](ClO4)2 or [Ni(Ph-TPY)2](ClO4)2, bis[4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine]manganese(II) bis(perchlorate), [Mn(C22H17N3O)2](ClO4)2 or [Mn(MeOPh-TPY)2](ClO4)2, and bis(4'-phenyl-2,2':6',2''-terpyridine)manganese(II) bis(perchlorate), [Mn(C21H15N3)2](ClO4)2 or [Mn(Ph-TPY)2](ClO4)2. In all three cases, the complexes present distorted octahedral coordination polyhedra and the crystal packing is determined mainly by weak C-H...π interactions. All the compounds (except for the Ni derivatives, for which FT-IR, UV-Vis and thermal analysis are reported) were fully characterized by spectroscopic (FT-IR, UV-Vis and NMR spectroscopy) and thermal (TGA-DSC, thermogravimetric analysis-differential scanning calorimetry) methods.

On-off switch of charge-separated states of pyridine-vinylene-linked porphyrin-C60 conjugates detected by EPR.

The design, synthesis, and electronic properties of a new series of D-π-A conjugates consisting of free base (H2P) and zinc porphyrins (ZnP) as electron donors and a fullerene (C60) as electron acceptor, in which the two electroactive entities are covalently linked through pyridine-vinylene spacers of different lengths, are described. Electronic interactions in the ground state were characterized by electrochemical and absorption measurements, which were further supported with theoretical calculations. Most importantly, charge-transfer bands were observed in the absorption spectra, indicating a strong push-pull behavior. In the excited states, electronic interactions were detected by selective photoexcitation under steady-state conditions, by time-resolved fluorescence investigations, and by pump probe experiments on the femto-, pico-, and nanosecond time scales. Porphyrin fluorescence is quenched for the different D-π-A conjugates, from which we conclude that the deactivation mechanisms of the excited singlet states are based on photoinduced energy- and/or electron transfer processes between H2P/ZnP and C60, mediated through the molecular spacers. The fluorescence intensity decreases and the fluorescence lifetimes shorten as the spacer length decreases and as the spacer substitution changes. With the help of transient absorption spectroscopy, the formation of charge-separated states involving oxidized H2P/ZnP and reduced C60 was confirmed. Lifetimes of the corresponding charge-separated states, which ranged from ∼400 picoseconds to 165 nanoseconds, depend on the spacer length, the spacer substitution, and the solvent polarity. Interestingly, D-π-A conjugates containing the longest linkers did not necessarily exhibit the longest charge-separated state lifetimes. The distances between the electron donors and the acceptors were calculated by molecular modelling. The longest charge-separated state lifetime corresponded to the D-π-A conjugate with the longest electron donor-acceptor distance. Likewise, EPR measurements in frozen media revealed charge separated states in all the D-π-A conjugates investigated. A sharp peak with g values ∼2.000 was assigned to reduced C60, while a broader, less intense signal (g ∼ 2.003) was assigned to oxidized H2P/ZnP. On-off switching of the formation and decay of the charge-separated states was detected by EPR at 77 K by repeatedly turning the irradiation source on and off.

3-(4-Bromo-phen-yl)-N,N-dimethyl-3-oxopropan-1-aminium chloride.

The title compound, C(11)H(15)BrNO(+)·Cl(-), was obtained as a precursor within our current program for the synthesis of new ß-amino-alcohols via a Mannich-type reaction. The protonated amino N atom is hydrogen bonded to the chloride anion. With exception of one methyl group, the cation is approximately planar (r.m.s. deviation for all non H-atoms = 0.069 Å).