Soret Absorption Band Research Articles

Downhill excitation energy flow in reaction centers of purple bacteria Rhodospirillum rubrum G9

Using femtosecond differential spectroscopy, excitation energy transfer in reaction centers (RCs) of the carotenoidless strain of purple bacteria Rhodospirillum rubrum G9 was studied at room temperature. Excitation and probing of the Qy, Qx and Soret absorption bands of the RCs were carried out by pulses with duration of 25–30 fs. Modeling of ΔA (light – dark) kinetics made it possible to estimate the characteristic time of various stages of excitation energy transformation. It is shown that the dynamics of the downhill energy flow in the RCs is determined both by the internal energy conversion Soret→ Qx → Qy in each cofactor and by the energy transfer H* → B* → P* (H – bacteriopheophytin, B – bacteriochlorophyll a, P – bacteriochlorophyll a dimer) between cofactors. The transfer of energy between the upper excited levels (Soret and Qx) of the cofactors accelerates its arrival to the lower exciton level of the P, from where charge separation begins. It turned out that all conversion and energy transfer processes occur within 40–160 fs: the conversion Soret → Qx occurs in 40–50 fs, the conversion Qx → Qy occurs in 100–140 fs, the transfer H* → B* has a time constant of 80–120 fs, and the transfer B* → P* has a time constant of 130–160 fs. The rate of energy transfer between the upper excited levels is close to the rate of transfer between Qy levels.

Excited Charge Separation in a π-Interacting Phenothiazine-Zinc Porphyrin-Fullerene Donor-Acceptor Conjugate.

We have designed, synthesized, and characterized a donor-acceptor triad, SPS-PPY-C60, that consists of a π-interacting phenothiazine-linked porphyrin as a donor and sensitizer and fullerene as an acceptor to seek charge separation upon photoexcitation. The optical absorption spectrum revealed red-shifted Soret and Q-bands of porphyrin due to charge transfer-type interactions involving the two ethynyl bridges carrying electron-rich and electron-poor substituents. The redox properties suggested that the phenothiazine-porphyrin part of the molecule is easier to oxidize and the fullerene part is easier to reduce. DFT calculations supported the redox properties wherein the electron density of the highest molecular orbital (HOMO) was distributed over the donor phenothiazine-porphyrin entity while the lowest unoccupied molecular orbital (LUMO) was distributed over the fullerene acceptor. TD-DFT studies suggested the involvement of both the S2 and S1 states in the charge transfer process. The steady-state emission spectrum, when excited either at porphyrin Soret or visible band absorption maxima, revealed quenched emission both in nonpolar and polar solvents, suggesting the occurrence of excited state events. Finally, femtosecond transient absorption spectral studies were performed to witness the charge separation by utilizing solvents of different polarities. The transient data was further analyzed by GloTarAn by fitting the data with appropriate models to describe photochemical events. From this, the average lifetime of the charge-separated state calculated was found to be 169 ps in benzonitrile, 319 ps in dichlorobenzene, 1.7 ns in toluene for Soret band excitation, and ∼320 ps for Q-band excitation in benzonitrile.

Supramolecular chirality in self-assembly of zinc protobacteriochlorophyll-d analogs possessing enantiomeric esterifying groups

Zinc 3-hydroxymethyl-pyroprotopheophorbides-a esterified with a chiral secondary alcohol at the 17-propionate residue were prepared as bacteriochlorophyll-d analogs. The synthetic zinc 31-hydroxy-131-oxo-porphyrins self-aggregated in an aqueous Triton X-100 micellar solution to give red-shifted and broadened Soret and Qy absorption bands in comparison with their monomeric bands. The intense, exciton-coupled circular dichroism spectra of their self-aggregates were dependent on the chirality of the esterifying groups. The observation indicated that the self-aggregates based on the J-type stacking of the porphyrin cores were sensitive to the peripheral 17-propionate residues. The supramolecular structures of the present J-aggregates as models of bacteriochlorophyll aggregates in natural chlorosomes were remotely regulated by the esterifying groups.Graphical abstract

Linear Extension of Carbaporphyrin Chromophores: Synthesis, Protonation, and Metalation of Anthro[2,3-b]carbaporphyrins: Evidence for 30π-Electron Aromatic Circuits in a Palladium(II) Complex.

Acid-catalyzed condensation of a naphtho[2,3-f]indane dialdehyde with a tripyrrane, followed by an oxidation step, afforded an anthro[2,3-b]-21-carbaporphyrin. The presence of a fused anthracene unit induced minor bathochromic shifts and did not significantly affect the aromatic characteristics of the carbaporphyrin core. Protonation led to the formation of a monocation with similar diatropic properties, but the dication generated in the presence of a large excess of trifluoroacetic acid had a weakened Soret band absorption and a broad absorption at 754 nm. Nucleus-independent chemical shift (NICS) calculations indicate that the dication is only weakly aromatic and possesses a 32-atom 30π electron delocalization pathway. Alkylation with methyl iodide and potassium carbonate gave a 22-methyl derivative that reacted with palladium(II) acetate to afford an aromatic palladium(II) complex. Upon heating, the methyl group migrated from the nitrogen to the internal carbon atom and the resulting complex exhibited diminished aromatic character. A comparison with related carbaporphyrin complexes without ring fusion or with benzo- or naphtho-fused units demonstrated that the diatropic character decreased with increasing conjugation. NICS calculations and anisotropy of induced current density (AICD) plots confirmed this trend and showed that the remaining aromatic properties of the anthrocarbaporphyrin complex were due to a 30π electron circuit that extends around the entire anthracene unit.

Synthesis of C3-substituted chlorophyll-a derivatives fused by a π-conjugated E-ring and their physical properties with unique near-infrared absorption

Chlorophylls (Chls) are one of the most important pigments for the light-harvesting systems in photosynthesis. Methyl pheophorbide-a derivative fused by a π-conjugated E-ring with the C131=C132 double bond was found as a synthetic example of the unique Chl-a derivatives, which showed split Soret absorption bands in the purple and ultraviolet-A regions and a broad absorption band at a near-infrared (NIR) region as its monomeric state, but not its self-aggregated species. The 3-vinyl group of the Chl-a derivative was chemically transformed into ethyl, formyl, hydroxymethyl, and dialkoxymethyl groups. All the resulting chlorins exhibited unique wide bands at a NIR region. The substitution effect on the peaks of their wide NIR bands was similar to that on the sharp redmost Qy maxima at a visible region of the corresponding pheophorbides with the C131–C132 single bond. Protons at the C5-, C10-, and C20-positions as well as of the peripheral C2-, C3-, C7-, and C8-substituents of methyl 3-substituted 131,132-didehydro-131-deoxo-pheophorbides-a were upfield-shifted in 1H nuclear magnetic resonance, compared with those of intact pheophorbides. The shifts were ascribed to the less ring current of the cyclic tetrapyrroles by π-conjugation of the E-ring. The non-fluorescent C3-substituted Chl-a derivatives could be useful as new materials absorbing NIR wavelength light.

Reversible disassembly-reassembly of C-phycocyanin in pressurization-depressurization cycles of high hydrostatic pressure

Hydrostatic pressure can reversibly modulate protein-protein and protein-chromophore interactions of C-phycocyanin (C-PC) from Spirulina platensis. Small-angle X-ray scattering combined with UV–Vis spectrophotometry and protein modeling was used to explore the color and structural changes of C-PC under high pressure conditions at different pH levels. It was revealed that pressures up to 350 MPa were enough to fully disassemble C-PC from trimers to monomers at pH 7.0, or from monomers to detached subunits at pH 9.0. These disassemblies were accompanied by protein unfolding that caused these high-pressure induced structures to be more extended. These changes were reversible following depressurization. The trimer-to-monomer transition proceeded through a collection of previously unrecognized, L-shaped intermediates resembling C-PC dimers. Additionally, pressurized C-PC showed decayed Q-band absorption and fortified Soret-band absorption. This was evidence that the folded tetrapyrroles, which had folded at ambient pressure, formed semicyclic unfolded conformations at a high pressure. Upon depressurization, the peak intensity and shift all recovered stepwise, showing pressure can precisely manipulate C-PC's structure as well as its color. Overall, a protein-chromophore regulatory theory of C-PC was unveiled. The pressure-tunability could be harnessed to modify and stabilize C-PC's structure and photochemical properties for designing new delivery and optical materials.

Photosynthesis under a red Sun: predicting the absorption characteristics of an extraterrestrial light-harvesting antenna

ABSTRACT Here, we discuss the feasibility of photosynthesis on Earth-like rocky planets in close orbit around ultracool red dwarf stars. Stars of this type have very limited emission in the photosynthetically active region of the spectrum (400–700 nm), suggesting that they may not be able to support oxygenic photosynthesis. However, photoautotrophs on Earth frequently exploit very dim environments with the aid of highly structured and extremely efficient antenna systems. Moreover, the anoxygenic photosynthetic bacteria, which do not need to oxidize water to source electrons, can exploit far-red and near-infrared light. Here, we apply a simple model of a photosynthetic antenna to a range of model stellar spectra, ranging from ultracool (2300 K) to Sun-like (5800 K). We assume that a photosynthetic organism will evolve an antenna that maximizes the rate of energy input while also minimizing fluctuations. The latter is the noise cancelling principle recently reported by Arp et al. Applied to the solar spectrum, this predicts optimal antenna configurations in agreement with the chlorophyll Soret absorption bands. Applied to cooler stars, the optimal antenna peaks become redder with decreasing stellar temperature, crossing to the typical wavelength ranges associated with anoxygenic photoautotrophs at ∼3300 K. Lastly, we compare the relative input power delivered by antennae of equivalent size around different stars and find that the predicted variation is within the same order of magnitude. We conclude that low-mass stars do not automatically present light-limiting conditions for photosynthesis, but they may select for anoxygenic organisms.

Laterally Bound Co Porphyrin on CdTe QD: A Long-Lived Charge-Separated Nanocomposite

Cobalt porphyrin (CoP) derivatives are potential compounds for photocatalytic CO2 reduction which must be activated by photoinduced electron transfer from a suitable electron donor. Herein, we have prepared and studied the photophysics of CdTe quantum dots (CQD) coupled with CoP derivatives where CQDs act as the light antenna and the electron donor and CoP acts as the electron acceptor. To facilitate the nanocomposite formation of CoP with CQD, CoP has been equipped with a −COOH anchoring group which leads to strong complexation between CQD and CoP as observed in the absorption spectra by a gradual shift in the Soret absorption band. This is attributed to the lateral binding geometry of CoP through the −COOH anchoring group and Co-center coordination to CQD, which helps to bring CoP close to the CQD. Our DFT calculations have identified that this lateral geometry is more favorable than the upright orientation on the CdTe (110) surface. The redox levels have been determined from cyclic voltammetry which shows that the electron transfer (ET) from CQD to CoP is feasible. The strong luminescence quenching of CQD in the presence of CoP has also suggested quantitative CQD/CoP nanocomposite formation and pointed to the ET from QDs to CoP. The charge carrier dynamics have been monitored using femtosecond transient absorption (TA) spectroscopy. The TA spectral analysis has shown efficient ET in CQD/CoP which proves that our 4 nm CQD acts as an efficient electron donor for the CoP counterpart. The CQD excited state lifetime is shortened along with delayed Soret band bleaching of CoP in this nanocomposite. From the global fitting of TA data, the estimated average ET time constant from CQD to a CoP molecule is approximately 70 ps, and the charge recombination time is ≫5 ns. Also, differences in the TA spectra after ET have been observed which can be associated with the changes in the binding geometry of CoP on the CQD surface, which is lateral in the case of the ground-state complex to the upright orientation after the ET process. Hence, the studied CQD/CoP nanocomposites are promising materials to initiate CO2 reduction through photoexcitation of the CQD that activates the CoP molecular catalyst through the ET.

Label-free imaging of red blood cells and oxygenation with color third-order sum-frequency generation microscopy

Mapping red blood cells (RBCs) flow and oxygenation is of key importance for analyzing brain and tissue physiology. Current microscopy methods are limited either in sensitivity or in spatio-temporal resolution. In this work, we introduce a novel approach based on label-free third-order sum-frequency generation (TSFG) and third-harmonic generation (THG) contrasts. First, we propose a novel experimental scheme for color TSFG microscopy, which provides simultaneous measurements at several wavelengths encompassing the Soret absorption band of hemoglobin. We show that there is a strong three-photon (3P) resonance related to the Soret band of hemoglobin in THG and TSFG signals from zebrafish and human RBCs, and that this resonance is sensitive to RBC oxygenation state. We demonstrate that our color TSFG implementation enables specific detection of flowing RBCs in zebrafish embryos and is sensitive to RBC oxygenation dynamics with single-cell resolution and microsecond pixel times. Moreover, it can be implemented on a 3P microscope and provides label-free RBC-specific contrast at depths exceeding 600 µm in live adult zebrafish brain. Our results establish a new multiphoton contrast extending the palette of deep-tissue microscopy.

Renaturation of Myoglobin Denatured by Sodium Dodecyl Sulfate by Removal of Dodecyl Sulfate Ions Bound to the Protein Using Sodium Cholate.

The secondary and tertiary structures of myoglobin were disrupted by sodium dodecyl sulfate (SDS) but were hardly affected by the bile salt, sodium cholate (NaCho). This disruption was induced by the binding of dodecyl sulfate (DS) ions to the protein. In this study, the removal of DS ions bound to the protein was attempted using NaCho. The extent of removal of DS ions was estimated by the restoration of the secondary and tertiary structures of the protein disrupted by SDS. The secondary structural change was followed by monitoring mean residue ellipticity at 222 nm, [θ]222, which was frequently used as a measure of α-helical content. The tertiary structural change was followed by examining the Soret band absorbance of the protein. Evidently, the magnitude of [θ]222 of myoglobin in the SDS solution initially decreased and then increased back to almost its original value as the NaCho concentration increased. The initial decrease in [θ]222 indicated the cooperation of NaCho and SDS in disrupting the secondary structure at low concentrations of both surfactants. This cooperation was also observed in the tertiary structural change as a shift of the Soret band maximum wavelength, λmax, and a decrease in the molar absorption coefficient, εmax, at λmax. Above a certain NaCho concentration, the position of λmax and the magnitude of εmax were also restored to their original states. The secondary and tertiary structures were simultaneously restored by adding NaCho. These recoveries were attributed to removal of the DS ions bound to the protein. This removal might be due to the ability of cholate anions to strip DS ions bound to the protein. The stripped DS ions are more likely to form SDS-NaCho mixed micelles in bulk than SDS-NaCho mixed aggregates on the protein.

Fluorescence Anisotropy in Radachlorin and Chlorin e6 in Water–Methanol Solutions under One- and Two-Photon Excitation

The fluorescence anisotropy of photosensitizers Radachlorin and chlorin e6 was studied using the time-resolved single photon-counting technique under one- and two-photon excitation within the Soret absorption band. A very small negative anisotropy was observed in both photosensitizers under one-photon excitation in the vicinity of the absorption maximum within the wavelength range of 395–405 nm. Meanwhile, two-photon excitation of the photosensitizers in the same spectral range demonstrated high fluorescence anisotropy with the maximum value of about 0.43. The drastic difference of the fluorescence anisotropy parameters at one- and two-photon excitation modes was suggested to be due to the different symmetries of one- and two-photon absorption tensors when two-photon absorption tensor components have comparable values. The variation of excitation wavelengths in the spectral range of 375–425 nm demonstrated nonlinear wavelength dependence of anisotropy of both Radachlorin and chlorin e6, with opposite tendencies at one- and two-photon excitation. The data obtained suggest that one-photon excitation at about 405 nm often utilized in FLIM experiments is not sensitive to fluorescence anisotropy in Radachlorin and chlorin e6 and therefore cannot be used for the determination of anisotropy/rotational diffusion time in these molecules. Meanwhile, two-photon excitation can provide high fluorescence anisotropy and accurate determination of the rotational diffusion time. At the same time, one-photon excitation at about 405 nm can be used for the accurate evaluation of fluorescence lifetimes within the standard FLIM schematic where fluorescence polarization is not taken into account.

Individual heme a and heme a3 contributions to the Soret absorption spectrum of the reduced bovine cytochrome c oxidase

Bovine cytochrome c oxidase (CcO) contains two hemes, a and a3, chemically identical but differing in coordination and spin state. The Soret absorption band of reduced aa3-type cytochrome c oxidase consists of overlapping bands of the hemes a2+ and a32+. It shows a peak at ∼444 nm and a distinct shoulder at ∼425 nm. However, attribution of individual spectral lineshapes to hemes a2+ and a32+ in the Soret is controversial. In the present work, we characterized spectral contributions of hemes a2+ and a32+ using two approaches. First, we reconstructed bovine CcO heme a2+ spectrum using a selective Ca2+-induced spectral shift of the heme a2+. Second, we investigated photobleaching of the reduced Thermus thermophilus ba3- and bovine aa3-oxidases in the Soret induced by femtosecond laser pulses in the Q-band. The resolved spectra show splitting of the electronic B0x-, B0y-transitions of both reduced hemes. The heme a2+ spectrum is shifted to the red relative to heme a32+ spectrum. The ∼425 nm shoulder is mostly attributed to heme a32+.

A FRET sensor based on quantum dots-porphyrin assembly for Fe(III) detection with ultra-sensitivity and accuracy.

Exploring sensors based on Förster resonance energy transfer (FRET) systems enables the continuous development of biological sensing technologies. Herein, we report the construction of a FRET sensor with dual-emissive quantum dots (QDs) and meso-tetra(4-sulfonatophenyl) porphine (TSPP). The sensor is composed of mesial green-emissive QDs with a thick silica shell (gQD@SiO2) and circumjacent blue-emissive QDs coated with ultra-thin silica spacer, on which is linked TSPP (bQD@SiO2-TSPP). The gQD@SiO2 endows the sensor with a fluorescent background. Due to the ultra-thin silica spacing, coupled with the superior resonance effect of bQD fluorescence and the Soret-band absorption of TSPP, the FRET efficiency is highly sensitive to the chelation state of TSPP. Relying on the absorbance transition of TSPP complexed with Fe(III), the FRET sensor is applied for ultra-sensitive Fe(III) detection. In aqueous solution, the sensor is demonstrated to linearly detect Fe(III) in the range of 0-1μM, with a limit of detection (LOD) of 40nM. More importantly, reliable Fe(III) detection can be achieved via the specific complexation of Fe(III) by TSPP and the ratiometric fluorescent response. As such, the inter-/intra-day precisions in standard samples, as well as the recovery rate in biological matrices, are fully validated. The excellent analytical performance, in combination with the excellent biocompatibility of the FRET sensor, allows semi-quantitative Fe(III) imaging in living cells.

Three-dimensional Cd(ii) porphyrin metal–organic frameworks for the colorimetric sensing of Electron donors

Three MOFs with metalloporphyrin lined, large square 1D channels were used as colorimetric sensors for electron donors. Exposure to amine vapours caused a redshift of the Soret absorption bands of the metalloporphyrin.

Mode of action of the sesquiterpene lactones eupatoriopicrin and estafietin on Trypanosoma cruzi

Background: The sesquiterpene lactones (STLs) eupatoriopicrin (EP) and estafietin (ES), isolated from Stevia alpina Griseb. (Asteraceae) and Stevia maimarensis (Hieron.) Cabrera (Asteraceae) respectively, have previously showed promising trypanocidal activity, both in vitro and in vivo. Purpose: In this work, using biochemical studies and electron microscopy, we aimed at characterizing the mode of action of both STLs on Trypanosoma cruzi. Methods: The interaction of STLs with hemin was examined by measuring modifications in the Soret absorption band of hemin; the thiol groups interaction was determined spectrophotometrically through its reaction with 5,5’-dithiobis-2-nitrobenzoate; the effect on cruzipain activity was also assayed by spectrophotometry. The synthesis of sterols were qualitatively and quantitatively tested by TLC. Mitochondrial functionality was assessed by measuring mitochondrial membrane potential and the activity of NADH-cytochrome c reductase and succinate-cytochrome c reductase enzymes. The status of the antioxidant system was assessed by quantifying the level of free thiols by spectrophotometry, together with the intracellular oxidative state by flow cytometry. Ultrastructural changes were analyzed by transmission electron microscopy. Results: EP and ES were found to impair the functionality and the redox status of the parasite. ES produced a greater decrease in the activity of succinate dehydrogenase than eupatoriopicrin, affecting the functioning of the respiratory chain and the Krebs cycle. EP increased the formation of triglycerides leading to the presence of cytoplasmic lipid droplets. By electron microscopy, alterations in the kinetoplast and the appearance of large translucent vacuoles in the cytoplasm were observed for both compounds. Conclusions: Both sesquiterpenelactones proved to act additively on T. cruzi, supporting the hypothesis that each compound would be acting on different primary targets.. The treatment combining eupatoriopicrin and estafietin could be considered a promising alternative for the treatment of Chagas’ disease.

Difluoroboron complexes of peripheral β-diketonates in cyclopheophorbides: Their syntheses and optical properties

Cyclopheophorbide-a prepared from intramolecular mixed Claisen condensation of methyl pyropheophorbide-a (one of the chlorophyll-a derivatives) was complexed with a difluoroboron species at the β-diketonate moiety on the exo-five-membered ring fusing the core cyclic tetrapyrrole π-skeleton. Its 3-substituted chlorin analogs and the related bacteriochlorin were also synthesized by difluoroboronation of the corresponding (bacterio)chlorins possessing a peripheral diketonate group. In solution, all the synthetic complexes showed broad Qy and redmost Soret absorption bands and an intense bluemost Soret band. Their maxima were dependent on the 3-substitution and the 7,8-dihydrogenation. The boron complexes were non-fluorescent, which was comparable to the boron-free counterparts.

Solvent Effects on the Phosphorescence of Gold(III) Complexes Chelated by β-Multisubstituted Corroles.

A set of gold corrole complexes containing four different β-substituent groups (Br/I/CF3), namely, 4Br-Au, 4I-Au, and 4CF3-Au, were investigated; all showed room temperature phosphorescence. The phosphorescence quantum yields of the corroles were determined using tetraphenylporphyrin as a reference: Φph (4I-Au, 0.75%) > Φph (4Br-Au, 0.64%) > Φph (4CF3-Au, 0.38%). 4CF3-Au exhibited near-IR emission (858 nm, aerobic); absorbance intensity for the Q-band was higher than that for the Soret band. Complex 4I-Au showed a longer phosphorescence lifetime (82 μs) compared to those of 4Br-Au (53 μs) and 4CF3-Au (28 μs; N2, tol). Thermally activated delayed fluorescence (TADF) emission of 4I/Br-Au complexes was observed: stronger emission intensity correlated with increasing temperature. Good negative correlations for 4I/Br-Au were observed between the Soret band absorption energy and the solvent polarizability: excited states of 4I/Br-Au are more polar than their ground states. TD-DFT calculations revealed very fast intersystem crossing (ISC) rate constants, 2.20 × 1012 s-1 (4CF3-Au) > 1.96 × 1011 s-1 (4Br-Au) > 1.15 × 1011 s-1 (4I-Au), and importantly, the reverse intersystem crossing (rISC) rate constants are determined as 1.68 × 107 s-1 (4I-Au) > 2.40 × 103 s-1 (4Br-Au) ≫ 8.09 × 10-8 s-1 (4CF3-Au). The exceptionally low rISC rate constant of 4CF3-Au is attributed to its more steric and deformed structure bearing a larger energy gap between the S1 and T1 states.

High Pressure Treatment Modifies Rigid Structure of Myoglobin and Improves Its Digestibility

Abstract Objectives Myoglobin is a special globular protein composed of a polypeptides chain and a heme group. Our previous in vitro and in vivo studies have shown that myoglobin is less susceptible to digestion because of its rigid structure. High pressure treatment is gaining more and more popularity in meat industry. To improve the digestibility and nutritional value of myoglobin, the effects of high pressure treatment on the structural and nutritional properties of myoglobin were investigated. Methods Myoglobin was treated during 100–400 MPa for 20 min, spectroscopic techniques and an in vitro digestion model were performed. Results High pressure treatment induced unfolding of globin and dissociation of heme, with an increase in the absorbance of Soret band and a reduction in the intensity of intrinsic and synchronous fluorescence spectra. Some certain changes occurred in the dissociated heme group, as the content of heme and metmyoglobin decreased. The gastric and intestinal digestibility of myoglobin increased as the pressure rose. Conclusions The results indicated that high pressure treatment could be a promising technology to improve digestibility of myoglobin by modifying its structure to improve its nutritional value. Funding Sources This work was supported by the grants from NSFC (32072211).

Design of flexible dendritic systems bearing donor-acceptor groups (pyrene-porphyrin) for FRET applications

Herein, we report the synthesis and characterization of a novel series of dendritic compounds, bearing peripheral pyrene groups and a porphyrin core, of zero and first generation with different spacer lengths. These compounds were further metallated with Zn(II) and Mg(II). The optical properties of these dendritic molecules were studied by absorption and fluorescence spectroscopy. After metallation, the dendritic porphyrins exhibited a red shift in the Soret absorption band and a blue shift in the emission band. All compounds exhibited high energy transfer efficiency, reaching values of EFRET above 99%.

Synthesis of 18-formylated B-ring reduced chlorophyll derivative as a heme A analog and effect of the 18-substituent on optical properties

Methyl 17,18-didehydro-pyrobacteriopheophorbides-a possessing the 18-formyl and hydroxymethyl groups as chlorophyllous analogs of hemes A and I, respectively, were prepared by chemically modifying the corresponding 18-methyl counterpart via 17,18-cis-dihydroxylation and successive acidic mono-dehydration. As an increase of the oxidation degree in the 18-substituent (CH3 < CH2OH < CHO), the Soret and Qx absorption bands in dichloromethane were red-shifted, the Qy maxima were blue-shifted, and the relative intensities of the Qy over Soret bands decreased. The 18-formylated chlorin was less fluorescent than the 18-(hydroxy)methylated chlorins. The substitution effect was comparable to that at the 7-position in D-ring reduced chlorins, including chlorophylls-a/b.