Splitting Of Soret Band Research Articles

Polymeric Ladderphanes

A new class of polymers, which have a double-stranded polybinorbornene skeleton with multilayer planar oligoaryl linkers, defined as polymeric ladderphanes, are synthesized. The structures of these ladderphanes are determined by spectroscopic means. Photophysical studies and time-resolved fluorescence spectroscopic investigations reveal that there is a strong interaction between the chromophore linkers. Thus, Soret band splitting in the absorption spectrum of the polymer with porphyrin linker (12e), significant fluorescence quenching with oligoaryl linkers (12b-d), and excimer emission with a terphenylene-diethynylene linker (12a) are characteristic photophysical properties of these polymers. Scanning tunneling microscopy shows that polymers 12b and d exhibit a ladder-like morphology and form a supramolecular assembly leading to a two-dimensional ordered array on a highly oriented pyrolytic graphite surface.

Tunable Soret‐Band Splitting of an Amphiphilic Porphyrin by Surface Pressure

Porphyrin aggregates, that is, Jand H-aggregates, have attracted much attention because of their peculiar structural and photophysical properties, which make them potential candidates for applications in nonlinear optics, nanometer-sized photoconductors, light-harvesting systems, and catalysis. Porphyrin aggregation can be detected through spectrum changes of the degenerated Soret band. For freebase porphyrins with D2h symmetry, the degeneracy is theoretically lost. However, the absorption is not detectably split and a sole increased bandwidth is apparent with respect to porphyrins with D4h symmetry. [2] Such splitting can be detected for densely packed porphyrins as a function of the molecular organization. Thus, the Soret band of freebase porphyrins can be described in terms of two mutually perpendicular oscillators (namely, Bx, By). Soret-band splitting of porphyrins has been described before. However, controlling this phenomenon is difficult because of the high tendency of porphyrins to autoaggregate. A tunable Soret-band splitting is described in this communication for the first time in the same experiment. A novel amphiphilic porphyrin, namely, (OD)3TPPS3 (see Figure 1)—with a selected balance between three meso-phenyl groups possessing hydrophilic sulfonato moieties and one meso-phenyl group bearing three long hydrophobic alkoxy chains—is synthesized. The used patterns are known to produce ordered array structures in porphyrins and fullerenes. Figure 1 shows the p–A isotherm of (OD)3TPPS3 as well as the ellipsotherm (dD–A isotherms) on the basic subphase (pH 11, NaOH). The monolayer stability is analyzed by means of area–time diagrams and compression–expansion cycles (see the Supporting Information). The analysis reveals the formation of a stable monomolecular layer of (OD)3TPPS3 at the air–water interface. Moreover, from the ellipsometric study (see the Supporting Information), we calculate a thickness of 3.17 nm (A= 0.9 nm), which corresponds to a monolayer of upright porphyrins with perpendicular alkyl chains at the air–water interface for such a full-packing phase. Reflection spectroscopy of monolayers can selectively detect molecules at the air–water interface because of the reflectionenhanced effect that originates from absorption. Figure 2 shows reflection spectra (DR) of monolayers of (OD)3TPPS3 on Figure 1. Molecular structure of 5,10,15-tris(4-sulfonatophenyl)-20-(3,4,5-trin-octadecyloxyphenyl)porphyrin (OD)3TPPS3. p–A isotherm (c) and ellipsotherm, dD–A (g) of a monolayer of (OD)3TPPS3 at the air–water interface with basic subphase (pH 11, NaOH).

Synthesis and electronic properties of trimeric octaethylporphyrin (OEP) derivative connected with diacetylene linkage. A comparative study with vinylene-group connected OEP trimer

A new trimeric octaethylporphyrin (OEP) derivative was synthesized, in which each porphyrin ring is connected with diacetylene linkage. Its electronic absorption spectrum was examined, proving that the diacetylene linkage induces splitting of Soret band of OEP into two main bands with clear maxima at 429 and 481 nm and more bathochromic shift of Q band to appear in such a longer wavelength region atλmax=670 nm in chloroform, in contrast with that of the corresponding vinylene-group connected OEP trimer. It was shown that the spectrum of the present diacetylene-group connected OEP derivative drastically changed in pyridine, suggesting a coordination of pyridine molecule as the fifth ligand onto Ni(II) metal of the central ring. Furthermore, Vilsmeier formylation, a typical electrophilic substitution on the aromatic compounds, was examined for further oligomerization of OEP, proving that it takes place at the central ring exclusively.

Effects of a thiolate axial ligand on the pi-->pi* electronic states of oxoferryl porphyrins: a study of the optical and resonance Raman spectra of compounds I and II of chloroperoxidase.

Optical absorption and resonance Raman spectra have been investigated for enzymatic intermediates, compounds I and II, of chloroperoxidase (CPO) which contains a thiolate-ligated iron porphyrin. Compound I of CPO (CPO-I), an oxoferryl porphyrin pi cation radical, gave an apparently asymmetric single-peaked Soret band at 367 nm, for which band fitting analyses revealed the presence of two transition bands around 365 and 415 nm. Compound II of CPO (CPO-II), an oxoferryl neutral porphyrin, gave a split Soret spectrum with two bands (blue and red Soret bands) at 373 and 436 nm. Thus both CPO-I and CPO-II can be categorized as hyperporphyrins. The maximum extinction coefficients (epsilon(b) and epsilon(r)) and energies (Eb and Er) of the blue and red Soret bands of CPO-II were found to fall on an epsilon(b)/epsilon(r) versus Eb-Er correlation line derived from data reported for six-coordinate ferrous derivatives of cytochrome P450 and CPO. Corresponding data for CPO-I did not fall on the correlation line. Resonance enhancement of the FeIV=O stretching (vFeO) Raman band was found for CPO-I when Raman scattering was excited at wavelengths within both transition bands around 365 and 415 nm, while the vFeO Raman band was not identified for CPO-II at any of the excitation wavelengths examined here. These findings suggest that the thiolate axial ligand causes Soret band splitting of CPO-II through configuration interaction between the sulfur-->porphyrin e(g)* charge transfer and porphyrin a1u,a2u-->e(g)* transitions, while the FeO portion is important in determining the shape of the Soret band of CPO-I.

Molecular Organization of Porphyrin-Metal Complexes

Abstract Tetraethyltetramethylporphyrin substituted at two facing meso positions by N-methylimidazolyl groupings and its metal complexes were prepared. The absorption spectra of Zn and Mg complexes showed a characteristic splitting of Soret band and red-shifts of Q-bands indicating the exciton interaction of porphyrins in a slipped cofacial arrangement, where each imidazolyl group in one metal porphyrin is coordinated to metals in the other porphyrin skeleton. Typical upfield shifts in the 1H NMR spectra arising from such the stacking structure elucidated Zn and Mg complexes as a dimer and an oligomeric mixture, respectively. Bis(imidazolyl)substituted tetraethyltetramethyl-porphyrin was also prepared. It suggested the hydrogen bonded oligomer formation through imidazolyl-imidazolyl interactions in a columnar orientation. Electric conductivities of films prepared from these compounds werecharacterized. In a same line with behaviors in solution, samples capable of π-stacking interaction with adjacent porph...

Probing protein-cofactor interactions in the terminal oxidases by second derivative spectroscopy: study of bacterial enzymes with cofactor substitutions and heme A model compounds.

Second derivative absorption spectra are reported for the aa3-cytochrome c oxidase from bovine cardiac mitochondria, the aa3-600 ubiquinol oxidase from Bacillus subtilis, the ba3-cytochrome c oxidase from Thermus thermophilis, and the aco-cytochrome c oxidase from Bacillus YN-2000. Together these enzymes provide a range of cofactor combinations that allow us to unequivocally identify the origin of the 450-nm absorption band of the terminal oxidases as the 6-coordinate low-spin heme, cytochrome a. The spectrum of the aco-cytochrome c oxidase further establishes that the split Soret band of cytochrome a, with features at 443 and 450 nm, is common to all forms of the enzyme containing ferrocytochrome a and does not depend on ligand occupancy at the other heme cofactor as previously suggested. To test the universality of this Soret band splitting for 6-coordinate low-spin heme A systems, we have reconstituted purified heme A with the apo forms of the heme binding proteins, hemopexin, histidine-proline-rich glycoprotein and the H64V/V68H double mutant of human myoglobin. All 3 proteins bound the heme A as a (bis)histidine complex, as judged by optical and resonance Raman spectroscopy. In the ferroheme A forms, none of these proteins displayed evidence of Soret band splitting. Heme A-(bis)imidazole in aqueous detergent solution likewise failed to display Soret band splitting. When the cyanide-inhibited mixed-valence form of the bovine enzyme was partially denatured by chemical or thermal means, the split Soret transition of cytochrome a collapsed into a single band at 443 nm.(ABSTRACT TRUNCATED AT 250 WORDS)

The excited states of covalently linked dimeric porphyrins: I: The excited singlet states

The ground state absorbance and emission properties of a series of covalently linked biporphyrins were studied, in both their neutral and dicationic forms. The fluorescence quantum yields determined are comparable in value with that obtained from haematoporphyrin IX. Soret band splitting is observed for porphyrin rings separated by a hydrocarbon chain containing 0–3 carbons joined at the β,β′ ring positions. The biporphyrin linked directly at the meso position shows considerable steric hindrance and behaves like two independent chromophores.