tetraphenylporphine and zinc-hematoporphyrin

Two X-shaped, cruciform electron donor(2)-acceptor-acceptor'(2) (D(2)-A-A'(2)) molecules, 1 and 2, in which D = zinc 5-phenyl-10,15,20-tripentylporphyrin (ZnTPnP) or zinc 5,10,15,20-tetraphenylporphyrin (ZnTPP), respectively, A = pyromellitimide (PI), and A' = perylene-3,4:9,10-bis(dicarboximide) (PDI), were prepared to study self-assembly motifs that promote photoinitiated charge separation followed by electron and hole transport through π-stacked donors and acceptors. PDI secondary electron acceptors were chosen because of their propensity to form self-ordered, π-stacked assemblies in solution, while the ZnTPnP and ZnTPP donors were selected to test the effect of peripheral substituent steric interactions on the π-stacking characteristics of the cruciforms. Small- and wide-angle X-ray scattering measurements in toluene solution reveal that 1 assembles into a π-stacked structure having an average of 5 ± 1 molecules, when [1] =/~ 10(-5) M, while 2 remains monomeric. Photoexcitation of the π-stacked structure of 1 results in formation of ZnTPnP(•+)-PI-PDI(•-) in τ(CS1) = 0.3 ps, which is nearly 100-fold faster than the formation of ZnTPnP(•+)-PI(•-) in a model system lacking the PDI acceptor. The data are consistent with a self-assembled structure for 1 in which the majority of the intermolecular interactions have the ZnTPnP donor of one monomer cofacially π-stacked with the PDI acceptor of a neighboring monomer in a crisscrossed fashion. In contrast, 2 remains monomeric in toluene, so that photoexcitation of ZnTPP results in the charge separation reaction sequence: (1*)ZnTPP-PI-PDI → ZnTPP(•+)-PI(•-)-PDI → ZnTPP(•+)-PI-PDI(•-), where τ(CS1) = 33 ps and τ(CS2) = 239 ps. The perpendicular orientation of ZnTPnP and ZnTPP relative to PDI in 1 and 2 is designed to decrease the porphyrin-PDI distance without greatly decreasing the overall number of bonds linking them. This serves to decrease the Coulomb energy penalty required to produce D(•+)-PI-PDI(•-) relative to the corresponding linear D-PI-PDI array, while retaining the weak electronic coupling necessary to achieve long-lived charge separation, as evidenced by τ(CR) = 24 ns for ZnTPP(•+)-PI-PDI(•-).

Topics: Electron Transport; Electrons; Imides; Metalloporphyrins; Perylene; Porphyrins; Scattering, Small Angle; X-Ray Diffraction

Beta-nitroalkenyl meso-tetraphenylporphyrins [beta-TPPCHC(NO(2))R)], as free-bases and Zn(II) complexes, were studied by electrospray mass spectrometry (ESI-MS). Under this ionisation condition the [M + H](+) ions are formed. The fragmentation pattern of the resulting [M + H](+) ions were studied by electrospray tandem mass spectrometry (ESI-MS/MS). The ESI-MS/MS of beta- nitroalkenylporphyrins, either as free-bases or as Zn(II) complexes, show several interesting features, distinct from the typical behaviour of nitro compounds. For the studied compounds, common main fragmentation patterns are observed, namely characteristic losses of NO(2), HNO(2), 2OH, RNO(2), RCNO, RCNO(2), RCH(2)NO(2), C(6)H(5) plus NO(2) and the formation of the protonated macrocycle, [TPP + H](+) or [ZnTPP + H](+). However, depending on the presence or absence of the metal and the nature of the R substituent, important differences are observed on the relative abundances of the ions formed by the same fragmentation pathway. The presence of bromine in the alkenyl group leads to a peculiar behaviour, since the main fragmentation pattern corresponds to the combined elimination of the bromine atom with the typical nitro group fragments. When R = Br, the loss of the nitro group occurs in low relative abundance (11-16%). However, when R = CH(3), the relative abundance of the ion due to the loss of HNO(2) changes drastically from 100%, observed for the free-base porphyrin, to 29% in the case of the Zn(II) complex. These variations of the relative abundance of the fragment corresponding to the loss of the nitro moiety (typically considered as a diagnostic fragment) can induce to an erroneous interpretation of their MS/MS spectra. Some fragmentations are observed only for the free-base porphyrins, namely the loss of CH(NO(2)R and HNO(2) plus C(2)H(2), while the loss of OH, H(2)O, OH plus H(2)O and RCCH plus H(2)O is observed only for the complexes. Unusual and unexpected fragmentations are also observed, namely the losses of RCNO, RCNO(2) and HNO(2) plus C(2)H(2). This work demonstrates that valuable structural information about the beta-nitroalkenyl substituents linked to meso- tetraarylporphyrins can be achieved using MS/MS. These results can also be useful for the interpretation of the mass spectra of other nitroalkenyl substituted compounds.

Topics: Alkenes; Drug Design; Humans; Metalloporphyrins; Nitrogen; Porphyrins; Spectrometry, Mass, Electrospray Ionization

Covalent cavitand Zn(II)-porphyrins 17-20 were prepared via multistep syntheses. These host molecules show moderate to excellent binding affinities to N-methylimidazole and pyridine guests. The complexing behavior strongly depends on the spacer's length, number, and rigidity, in addition to the guest size. Cavitand capping and strapping of porphyrins strongly influence the complex formation and result in a 10-700-fold enhancement of the binding strength compared to tetraphenyl Zn(II)-porphyrin.

Topics: Imidazoles; Indicators and Reagents; Magnetic Resonance Spectroscopy; Metalloporphyrins; Models, Molecular; Porphyrins; Pyridines; Spectrophotometry, Ultraviolet