Andrei Y. Tauber

Ultrafast charge transfer in phytochlorin-[60]fullerene dyads: influence of the attachment position

Abstract A femtochemistry study has been performed on two phytochlorin–[60]fullerene donor–acceptor dyads, in which the fullerene moiety is linked via a pyrrolidine bridge either to the position 3 or 7 of the phytochlorin ring. Both dyads form an emissive intramolecular exciplex in less than 1 ps, but only the former dyad relaxes to the ground state via a charge transfer (CT) state.

Regioselective oxidation of the phytyl chain of pyrochlorophyll a

Abstract A regioselective oxidation of pyrochlorophyll a is described. Selenium dioxide is introduced for the hydroxylation or carbonylation of the P-4 allylic position in the phytyl chain ofthe phorbin.

Novel Model Compounds for Photoinduced Electron Transfer: Structures of the Folded Conformers of Zinc(II)–Pyropheophytin– Anthraquinone Dyads

The solution structures of the P4‐epimers of Zn(II)–pyropheophytin–anthraquinone dyads (ZnPQ1 and ZnPQ2) were determined using two‐dimensional NMR spectroscopy and molecular modeling. The mutual orientation of the anthraquinone and Zn–pyropheophytin rings was found to be different in the two P4‐epimeric dyads on the basis of the ROESY correlations, observed between the quinone and phorbin protons. The anthraquinone ring is situated below the phorbin macrocycle in both dyads, ZnPQ1 and ZnPQ2. In ZnPQ1, the ring planes show tilting, the anthraquinone ring being in a sloping position below subrings B, C and E of the phorbin macrocycle. In ZnPQ2, the two π‐systems are almost parallel with the anthraquinone ring being located approximately below the center of the phorbin macrocycle.

Synthesis of pyropheophytin-anthraquinone linked molecules as models for the study of photoinduced electron transfer

Abstract The first synthesis of pyropheophytin-anthraquinone compounds with the quinone covalently linked to the P4 allylic position of the phytyl chain is described. The results of preliminary conformational studies are reported for the two P4 stereoisomers obtained. These results suggest differences in the orientation of the anthraquinonyl-phytyl moiety relative to the phorbin macrocycle in the isomers.

Photoinduced energy and electron transfer of covalently linked zinc(II)-pyropheophytin-anthraquinone molecules in monolayers of Langmuir-Blodgett films

Abstract Electron donor-acceptor compounds of optically pure covalently linked Zn(II)-pyropheophytin-anthraquinone (ZnPQ) have been synthesized. These compounds allow one to prepare highly ordered solid samples by means of the Langmuir-Blodgett technique. Monolayer films of the P4( S )-ZnPQ diastereoisomer were prepared in a dioleoyl phosphatidylcholine matrix with the concentration varied from 0.5 to 10 mol.%. The time-resolved fluorescence properties of the films were interpreted in terms of the presence of two types of P4( S )-ZnPQ conformers, the folded one and the opened one. The folded conformer predominated and underwent fast intramolecular electron transfer (rate constant > 10 11 s −1 ) from the Zn-pyropheophytin part to the anthraquinone moiety and was, therefore, not observed directly in the fluorescence study. The open conformer had a relatively long-lived singlet excited state and was quenched by an energy transfer process to the folded conformer at P4( S )-ZnPQ concentrations higher than 2 mol.% with an estimated quenching radius of 5±0.2 nm.

An unexpected wittig reaction of dimethyl 3,3′-(3-formyl-2,7,12,18-tetramethyl-21H, 23H-porphyrin-13,17-diyl)-dipropionate

Abstract Transformation of one or both of the methoxycarbonyl groups of dimethyl 3,3′-(3-formyl-2,7,12,18-tetramethyl-21H,23H-porphyrin-13,17-diyl)-dipropionate (1) to isopropenyl groups was observed when an excess of ylide was used in the Wittig reaction.

Photophysical studies of 1,4-diazabicyclo(2,2,2)octane as a bifunctional ligand to fix the conformation of a flexibly-linked phorbinato-zinc dimer

Abstract The binding of a bifunctional ligand 1,4-diazabicyclo(2,2,2)octane (DABCO) to a phorbin-dimer (PP) in which a phytochlorin is covalently linked with a flexible spacer to a modified phytyl residue of pyropheophytin was studied in order to establish a rigid face-to-face intramolecular dimer. Steady-state and time-resolved fluorescence and absorption spectroscopies were employed to characterize the binding equilibrium in CH 2 Cl 2 and to verify the formation of a 1:1 complex where DABCO is bound between the Zn-phorbin rings of the dimer. The proportion of this complex is highest, about 88%, at the molar ratio of ligand:substrate=1.5:1 while at higher molar ratios, a second DABCO molecule binds to the dimer breaking down the fixed complex.