Carotenoid Moiety Research Articles

Semi‐Synthetic Chlorophyll‐Carotenoid Dyad for Dye‐Sensitized Photocatalytic Hydrogen Evolution

AbstractA chlorin‐carotenoid dyad Dyad‐COOH possessing a C32‐carboxylic acid group and a carotenoid moiety at the terminal end of C17‐substituent is synthesized from naturally occurring chlorophyll‐a as a new sensitizer for photocatalytic hydrogen evolution (PHE). Under the same experimental conditions, a maximum turnover number (TON) of PHE based on Dyad‐COOH/Pt/TiO2 is much higher than those of Pt/TiO2‐based photocatalysts sensitized by the corresponding chlorin carboxylic acid (Chl‐COOH) without carotenoid side chain, sole carotenoic acid (Car‐COOH), or their 1:1 (mol/mol) mixture. By co‐adsorbing different types of carboxylic acid, the TON of Chl‐COOH is found to be increased probably due to the suppression of chlorin aggregates on the TiO2 surface. The Dyad‐COOH/Pt/TiO2 exhibits excellent photocatalytic performance with the hydrogen evolution of 9147 µmol g−1 h−1 with TON of 425 when 43 µmol g−1 of dye is loaded on the Pt/TiO2 catalyst, while a better TON of 556 is achieved by preparing the photocatalyst with 10 µmol g−1 of Dyad‐COOH. This study provides new ideas for utilizing traditional photosynthetic dyes to a low‐cost and highly‐efficient photosensitizer for PHE.

Carotenoids as electron or excited-state energy donors in artificial photosynthesis: an ultrafast investigation of a carotenoporphyrin and a carotenofullerene dyad

Photophysical investigations of molecular donor-acceptor systems have helped elucidate many details of natural photosynthesis and revealed design principles for artificial photosynthetic systems. To obtain insights into the factors that govern the partition between excited-state energy transfer (EET) and electron transfer (ET) processes among carotenoids and tetrapyrroles and fullerenes, we have designed artificial photosynthetic dyads that are thermodynamically poised to favor ET over EET processes. The dyads were studied using transient absorption spectroscopy with ∼100 femtosecond time resolution. For dyad , a carotenoporphyrin, excitation to the carotenoid S2 state induces ultrafast ET, competing with internal conversion (IC) to the carotenoid S1 state. In addition, the carotenoid S1 state gives rise to ET. In contrast with biological photosynthesis and many artificial photosynthetic systems, no EET at all was detected for this dyad upon carotenoid S2 excitation. Recombination of the charge separated state takes place in hundreds of picoseconds and yields a triplet state, which is interpreted as a triplet delocalized between the porphyrin and carotenoid moieties. In dyad , a carotenofullerene, excitation of the carotenoid in the S2 band results in internal conversion to the S1 state, ET and probably EET to fullerene on ultrafast timescales. From the carotenoid S1 state EET to fullerene occurs. Subsequently, the excited-state fullerene gives rise to ET from the carotenoid to the fullerene. Again, the charge separated state recombines in hundreds of picoseconds. The results illustrate that for a given rate of EET, the ratio of ET to EET can be controlled by adjusting the driving force for electron transfer.

Controls on distributions of methylphenanthrenes in sedimentary rock extracts: Critical evaluation of existing geochemical data from molecular modelling

The thermodynamic stability of methylphenanthrene isomers and the kinetics of reactions involved in their natural destruction/formation have been studied via molecular modelling. The results were combined with published methylphenanthrene abundances in extracts of rocks containing Type III kerogen of a wide maturity range, to evaluate the utility of methylphenanthrene maturity parameters. These parameters track the isomer evolution toward equilibrium, leading to enrichment in the stable 2- and 3-methyl isomers relative to the less stable 9-, 1- and 4-methylisomers. The pathways from kinetically to thermodynamically controlled distributions remain unclear but probably involve isomerisation, transmethylation and demethylation reactions. To understand the importance of each pathway, ab initio quantum chemical calculations (DFT) have been performed, leading to the identification of possible transition states and to the determination of activation energies for reactions in aqueous solutions. Acid catalysis significantly lowers modelled reaction barriers to an extent consistent with the changes observed in nature. The equilibration can start at very low maturation with acid catalysed 1,2-methyl shifts (isomerisations) regarding low energy barriers: 15.1 kcal/mol from 4- to 3-, 22.5 kcal/mol from 1- to 2- and 30.2 kcal/mol from 3- to 2-methylphenanthrene. Alternative isomerisation pathways through tertiary carbon centres are ineffective. For example the isomerisation between the 9- and 1-isomer requires 39.7 kcal/mol, which is ca. 7 kcal/mol more than for demethylation coupled with methyl transfer to another molecule (transmethylation). A reverse transmethylation, e.g. modelled methylations of phenanthrene with either a terpenoid alcohol with a gem-dimethyl or polymethyl aryl carotenoid moiety can preferentially lead to 9-methylphenanthrene due to a relatively lower energy barrier. The appearance of 9-methylphenanthrene at very early maturation stages suggests effective heterogenic catalysis by the mineral matrix. The reaction is however reversible, which means that 9-methylphenanthrene tends to demethylate with much higher rates than the other isomers but only when suitable methyl acceptors are available. In turn, free radical demethylation which is likely at advanced levels of maturity would not significantly influence relative proportions of the isomers due to very similar barriers for all the isomers. However the reverse reaction would produce all isomers thus equalising all isomer concentrations. The discussed reactions are only a few of many reactions in which phenanthrene and methylphenanthrenes are potentially involved in nature to mention only biotic (biodegradation) and abiotic methylphenanthrene demethylation, and that there is no a single reaction that determines the fate of these molecules. Therefore, the commonly applied maturity index MPI-1 does not entirely reflect thermal maturity but is instead a molecular expression of complex processes and is dependent partly on catalytic effects of the mineral matrix. Analysis of the published data on methylphenanthrene abundance in rocks containing Type III kerogens indicates that there is no inversion of the MPI-1 trend above R r = 1.35% as has been suggested previously. The maturity parameter MPR, defined as the 2-/1-MP ratio seems more closely dependant on thermal maturity than MPI-1.

Carotenoids in a Corynebacterineae,Gordonia terraeAIST-1: Carotenoid Glucosyl Mycoloyl Esters

We isolated a strain of Corynebacterineae from surface seawater from the Inland Sea of Japan. This strain, AIST-1, was determined to be a strain of Gordonia terrae based on its 16S rRNA gene sequence. The colony was red-colored, and the pigments were identified to be carotenoid derivatives. The structures of two major carotenoids were (2'S)-deoxymyxol 1'-glucoside, a dihydroxyl derivative of gamma-carotene with 12 conjugated double bonds, and (2'S)-4-ketodeoxymyxol 1'-glucoside. Their glucosyl acyl esters and mycoloyl esters were also identified. While these carotenoid moieties have been found in only a few other bacteria, the carotenoid mycoloyl esters are novel carotenoid derivatives. The type strain of G. terrae NBRC 10016T also contained the same carotenoids, but the composition of the two carotenoid glucosides was low and the total carotenoid content was less than one tenth of that of strain AIST-1.

A dye-sensitized solar cell using pheophytin–carotenoid adduct: Enhancement of photocurrent by electron and singlet-energy transfer and by suppression of singlet–triplet annihilation due to the presence of the carotenoid moiety

Titania-based solar cells were fabricated by the use of a pheophytin derivative and a pheophytin–carotenoid adduct. The addition of the carotenoid moiety increased the photocurrent ( J sc = 3.7 → 6.0 mA cm −2), reduced the photovoltage ( V oc = 0.53 → 0.46 V), and enhanced the solar energy-to-electricity conversion efficiency ( η = 1.4 → 1.8%). The increase in photocurrent was explained in terms of electron and singlet-energy transfer from the carotenoid to the chlorin moiety as well as the prevention of the chlorin aggregate by the bulky carotenoid moiety and the resultant suppression of the singlet–triplet annihilation reaction.

Charge separation and energy transfer in a caroteno—C60 dyad: photoinduced electron transfer from the carotenoid excited states

We have designed and synthesized a molecular dyad comprising a carotenoid pigment linked to a fullerene derivative (C-C(60)) in which the carotenoid acts both as an antenna for the fullerene and as an electron transfer partner. Ultrafast transient absorption spectroscopy was carried out on the dyad in order to investigate energy transfer and charge separation pathways and efficiencies upon excitation of the carotenoid moiety. When the dyad is dissolved in hexane energy transfer from the carotenoid S(2) state to the fullerene takes place on an ultrafast (sub 100 fs) timescale and no intramolecular electron transfer was detected. When the dyad is dissolved in toluene, the excited carotenoid decays from its excited states both by transferring energy to the fullerene and by forming a charge-separated C.+ -C(60).- . The charge-separated state is also formed from the excited fullerene following energy transfer from the carotenoid. These pathways lead to charge separation on the subpicosecond time scale (possibly from the S(2) state and the vibrationally excited S(1) state of the carotenoid), on the ps time scale (5.5 ps) from the relaxed S(1) state of the carotenoid, and from the excited state of C(60) in 23.5 ps. The charge-separated state lives for 1.3 ns and recombines to populate both the low-lying carotenoid triplet state and the dyad ground state.

Tetrapyrrole Singlet Excited State Quenching by Carotenoids in an Artificial Photosynthetic Antenna

Two artificial photosynthetic antenna models consisting of a Si phthalocyanine (Pc) bearing two axially attached carotenoid moieties having either 9 or 10 conjugated double bonds are used to illustrate some of the function of carotenoids in photosynthetic membranes. Both models studied in toluene, methyltetrahydrofuran, and benzonitrile exhibited charge separated states of the type C*+-Pc*- confirming that the quenching of the Pc S1 state is due to photoinduced electron transfer. In hexane, the Pc S1 state of the 10 double bond carotenoid-Pc model was slightly quenched but the C*+-Pc*- transient was not spectroscopically detected. A semiclassical analysis of the data in hexane at temperatures ranging from 180 to 320 K was used to demonstrate that photoinduced electron transfer could occur. The model bearing the 10 double bond carotenoids exhibits biexponential fluorescence decay in toluene and in hexane, which is interpreted in terms of an equilibrium mixture of two isomers comprising s-cis and s-trans conformers of the carotenoid. The shorter fluorescence lifetime is associated with an s-cis carotenoid conformer where the close approach between the donor and acceptor moieties provides through-space electronic coupling in addition to the through-bond component.

Artificial Photosynthetic Reaction Centers with Carotenoid Antennas.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Electrochemical and EQCM investigation of a selenium derivatized carotenoid in the self-assembled state at a gold electrode

Abstract 1-(β-Apo-8′-carotenoyl)-2-(7-selenaoctanoyl)-glycerol was attached to the gold electrode surface by chemisorption from an acetonitrile solution and the surface layer was investigated by electrochemical methods and piezoelectric nanogravimetry in aqueous solutions. The adsorbate binds to the gold surface by the selenium end group and adopts a roughly perpendicular orientation to the electrode surface. The carotenoid moiety in the adsorbate undergoes an anodic reaction (peak potential, 0.78 V vs. Ag∣AgCl (1 M KCl) electrode) which occurs via an electron transfer followed by the uptake of two hydroxyls. Hydrogen radicals also form and initiate a polymerization process which leads to a more compact and rigid structure of the surface layer. At more positive potentials, the product of these reactions undergoes a slow oxidative desorption which is accompanied by gold oxidation and partial oxidation of organic selenium to SeO 3 2 - . Redox probe investigations revealed that the anodic reaction at 0.78 V results in major changes in the film structure and morphology. At a moderate coverage degree, electrochemically generated O2H radicals cause the fragmentation of the conjugated system by addition to the double bonds but do not induce a cross-linking reaction. No cathodic desorption of the CSeOG generated layer occurred in a 0.5 M KOH solution.

Artificial photosynthetic reaction centers with carotenoid antennas

Two reaction center-antenna models based on a purpurin macrocycle linked to a C 60 and to a carotenoid polyene have been synthesized. In these systems the C 60 moiety is the primary electron acceptor, the purpurin is the primary electron donor and the carotenoid moiety acts both as an antenna and secondary electron donor. Formation of the initial charge separated state, C–Pur + –C 60 − , following excitation with light absorbed by either the purpurin or C 60 takes place on the 10 ps time scale. The final charge separated state, C + –Pur–C 60 − , is formed in one of the compounds with a quantum yield of 32% based upon light absorbed by the carotenoid. In order to function as an antenna, the carotenoid pigment must be electronically coupled to the purpurin. The purpurin C ring provides an excellent framework for locating a carotenoid polyene in partial conjugation with the macrocycle, leading to a relatively strong electronic communication between the chromophores; functionalization of a meso position of the purpurin provides a site for the covalent attachment of C 60.

Artificial Photosynthetic Reaction Centers: Mimicking Sequential Electron and Triplet‐Energy Transfer

An artificial photosynthetic reaction center consisting of a carotenoid (C), a dimesitylporphyrin (P), and a bis(heptafluoropropyl)porphyrin (P(F)), C-P-P(F) , and the related triad in which the central porphyrin has been metalated to give C-P(Zn)-P(F) have been synthesized and characterized by transient spectroscopy. These triads are models for amphipathic triads having a carboxylate group attached to the P(F) moiety; they are designed to carry out redox processes across lipid bilayers. Triad C-P-P(F) undergoes rapid singlet-singlet energy transfer between the porphyrin moieties, so that their excited states are in equilibrium. In benzonitrile, photoinduced electron transfer from the first excited singlet state of P and hole transfer from the first excited singlet state of P(F) yield the initial charge-separated state C-P(.) (+)-P(F) (.) (-). Subsequent hole transfer to the carotenoid moiety generates the final charge-separated state C(.) (+)-P-P(F) (.) (-), which has a lifetime of 1.1 mus and is formed with a quantum yield of 0.24. In triad C-P(Zn)-P(F) energy transfer from the P(Zn) excited singlet to the P(F) moiety yields C-P(Zn)-(1)P(F) . A series of electron-transfer reactions analogous to those observed in C-P-P(F) generates C(.) (+)-P(Zn)-P(F) (.) (-), which has a lifetime of 750 ns and is formed with a quantum yield of 0.25. Flash photolysis experiments in liposomes containing an amphipathic version of C-P(Zn)-P(F) demonstrate that the added driving force for photoinduced electron transfer in the metalated triad is useful for promoting electron transfer in the low-dielectric environment of artificial biological membranes. In argon-saturated toluene solutions of C-P-P(F) and C-P(Zn)-P(F) , charge separation is not observed and a considerable yield of triplet species is generated upon excitation of the porphyrin moieties. In both triads triplet energy localized in the P(F) moiety is channeled to the carotenoid chromophore by a triplet energy-transfer relay mechanism. Certain photophysical characteristics of these triads, including the sequential electron transfer and the triplet energy-transfer relay mechanism, are reminiscent of those observed in natural reaction centers of photosynthetic bacteria.

Bioinspired energy conversion

Abstract Artificial photosynthetic antenna systems have been synthesized based on carotenoid polyenes and polymer-polyenes covalently attached to tetrapyrroles. Absorption of light in the blue/green region of the spectra excites the polyenes to their S2 state, and ultrafast singlet energy transfer to the tetrapyrroles occurs when the chromophores are in partial conjugation. The additional participation of other excited states of the polyene in the energy-transfer process is a requirement for perfect antenna function. Analogs of photosynthetic reaction centers consisting of tetrapyrrole chromophores covalently linked to electron acceptors and donors have been prepared. Excitation of these constructs results in a cascade of energy transfer/electron transfer which, in selected cases, forms a final charge-separated state characterized by a giant dipole moment (>150 D), a quantum yield approaching unity, a significant fraction of the photon energy stored as chemical potential, and a lifetime sufficient for reaction with secondary electron donors and acceptors. A new antenna-reaction center complex is described in which a carotenoid moiety is located in partial conjugation with the tetrapyrrole π-system allowing fast energy transfer (<100 fs) between the chromophores. In this assembly, the energy transduction process can be initiated by light absorbed by the polyene.

Electroconductive Langmuir-Blodgett films containing a carotenoid amphiphile for sugar recognition.

Fabrication of electroconductive molecules has attracted the most interest in nanotechnology. To date, molecules bearing a long conjugated bond have been synthesized, and they exhibited electric conduction. If molecular recognition sites could be attached to the conducting molecules, the conducting molecules can be connected with each other or wired to the desired joints, and further be applied to the chemical sensors or the nanoscale electric circuits. In this study, we synthesized a carotenoid amphiphile, which bears both the conducting part, a carotenoid moiety, and the molecular recognition site, a boronic acid moiety for specific binding of sugars. The carotenoid amphiphile was mixed with a polymerizable amphiphile, spread at the air-water interface to form a monolayer, and then polymerized by light. The resulting polymerized monolayer was deposited on gold electrodes. The electric conduction and the molecular recognition ability of the monolayer on the electrode were studied by cyclic voltammetry. The electrode responded preferentially to the redox-active sugar derivative in the solution. The electric conduction was also microscopically confirmed by the AFM-current imaging technique. This manuscript has demonstrated a key step for designing molecular electronic devices based on molecular assembling, by which molecules are orientated spontaneously.

Correlation of fluorescence quenching in carotenoporphyrin dyads with the energy of intramolecular charge transfer states. Effect of the number of conjugated double bonds of the carotenoid moiety

The electrochemistry of a series of non-symmetric synthetic carotenoids, with different conjugated double bounds chain lengths (5 to 11) is reported. The values of the first oxidation potentials of the carotenoids were evaluated by digital simulation of the experimental cyclic voltammograms. There is a clear relationship between calculated (AM1) HOMO energies of neutral carotenoids with their conjugated chain length, indicating that the change of solvation energy of carotenoids is small throughout the series, and that the electron-donating ability of carotenoids increases with the length of the conjugated chain. Carotenoids had been previously used to design carotenoporphyrin (C–P) molecular dyads. Carotenoid oxidation potentials and the reduction potential of the porphyrin moiety were used in order to calculate the energy of intramolecular charge transfer state in C–P dyads. Correlation of porphyrin fluorescence quenching of these dyads with the energy of the charge transfer state is reported, showing that effective quenching is only possible for carotenoids with more than eight conjugated double bonds.

Ultrafast Energy Transfer from a Carotenoid to a Chlorin in a Simple Artificial Photosynthetic Antenna

A model photosynthetic antenna system consisting of a carotenoid moiety covalently linked to a purpurin has been prepared to study singlet-singlet energy transfer from a carotenoid to a cyclic tetrapyrrole. Ultrafast fluorescence upconversion measurements of the carotenopurpurin dyad and an unlinked reference carotenoid demonstrate that the fluorescent S 2 excited state of the carotenoid model has a lifetime of 150 ′ 3 fs, whereas the corresponding excited state of the carotenoid in the carotenopurpurin dyad is quenched to 40 ′ 3 fs. This quenching is assigned to energy transfer from the S 2 state to the purpurin with a 73 ′ 6% efficiency, which is in accord with the 67 ′ 4% quantum yield obtained by steady-state fluorescence excitation measurements. Concomitant with the decay of the carotenoid S 2 excited state, a single-exponential rise of the excited S 1 state of the purpurin moiety was observed at 699 nm with a time constant of 64 fs. However, the decay of the fluorescence anisotropy was faster at this wavelength (40 fs) and isotropic rise times as short as 44 fs were determined at other emission wavelengths. The lifetime of the Si state of the carotenoid (7.8 ps) was the same in both the carotenoid model and the dyad. Taken together, these results unequivocally demonstrate that the S 2 state of the carotenoid moiety is the sole donor state in this efficient singlet-singlet energy transfer process. The simple dyad described in this work mimics the ultrafast energy transfer kinetics found in certain naturally occurring pigment protein complexes and is thus able to reproduce the high electronic coupling needed for efficient energy transfer from an extremely short-lived energy donor state.

High-density lipoprotein associated with secondary vitellogenesis in the hemolymph of the crayfish Cherax quadricarinatus

The high-density lipoproteins LPI and LPII were isolated from the hemolymph of the crayfish Cherax quadricarinatus by gradient ultracentrifugation and high-performance liquid chromatography (HPLC). Both lipoproteins contained a carotenoid moiety. LPI is comprised of a single polypeptide with an approximate molecular mass of 96 kDa. LPII was composed of two similar native components, LPIIa and LPIIb, both having polypeptides of 80 and 177 kDa. Both under natural conditions and after endocrine manipulations, LPI was present in males and in females, regardless of the female reproductive stage. LPII was present only in secondary-vitellogenic females, but not during the winter reproductive arrest period. LPII was also absent from young females that had received androgenic gland implants. LPII also appeared in the hemolymph of intersex individuals from which the androgenic gland had been removed. It is therefore suggested that LPII serves as a marker indicating the onset of secondary vitellogenesis in C. quadricarinatus females.

Photophysical characteristics of two model antenna systems: a fucoxanthin–pyropheoporbide dyad and its peridinin analogue

Photophysical investigations of a fucoxanthin–pheophorbide- a dyad and its peridinin analogue have revealed that the efficiency of carotenoid-to-pheophorbide transfer of singlet excitation and of pheophorbide-to-carotenoid transfer of triplet excitation depend markedly both on the solvent and on the dyad. Furthermore, the carotenoid moiety, whose first excited singlet state lies higher than that of its pheophorbide partner, is able to quench the fluorescence of the latter; such indirect quenching, which must entail a process other than the transfer of electronic excitation, might provide a channel for the dissipation of excess energy in some natural antenna systems.

Carotenohematoporphyrins as Tumor‐Imaging Dyes. Synthesis and In Vitro Photophysical Characterization*

Multichromophoric dyes for use in tumor imaging have been synthesized and photophysically characterized. Structurally, these dyes are dyads and triads that consist of one or two carotenoid polyenes covalently attached to hematoporphyrin (HP) or hematoporphyrin dimethyl ester (HPDME) moieties via ester linkages. The ground-state absorption of each compound shows that the electronic interaction between the chromophores is small. The fluorescence quantum yield for the dyad monocaroteno-HPDME is 0.033 and the dicaroteno-HPDME triads have yields between 0.016 and 0.007, all of which are reduced with respect to the parent compound HPDME (0.09). Global analysis of the transient fluorescence decays of the dyads and triads requires two exponential components (approximately 5-6 ns and approximately 1-2 ns) to fit the data, while a single exponential component with a lifetime of 9.3 ns describes the decay data of the parent HPDME. Possible mechanisms for the observed porphyrin fluorescence quenching by the nearby carotenoid are discussed. Nanosecond transient absorption reveals a carotene triplet with maximum absorption at 560 nm and a 5.0 microsecond lifetime. No transient was detected at 450 nm, indicating rapid (< or = 10 ns) triplet energy transfer from the hematoporphyrin to the carotenoid moieties in fluid as well as in rigid media. The yield of triplet energy transfer from the porphyrin to the carotenoid moiety is unity. Singlet oxygen (O2(1 delta g), studies support the transient absorption data, as none of these compounds is capable of sensitizing O2(1 delta g). Liposome vesicles were used to study the photophysical characteristics of the dyes in phospholipid membranes. Singlet oxygen was not sensitized by the dyads and triads in liposomes. Transient absorption measurements suggest that the triads are substantially aggregated within the phospholipid bilayer, whereas aggregation in the dyads is less severe.

Carotenohematoporphyrins as Tumor-Imaging Dyes. Synthesis and In Vitro Photophysical Characterization

Multichromophoric dyes for use in tumor imaging have been synthesized and photophysically characterized. Structurally, these dyes are dyads and triads that consist of one or two carotenoid polyenes covalently attached to hematoporphyrin (HP) or hematoporphyrin dimethyl ester (HPDME) moieties via ester linkages. The ground-state absorption of each compound shows that the electronic interaction between the chromophores is small. The fluorescence quantum yield for the dyad monocar-oteno- HPDME is 0.033 and the dicaroteno-HPDME triads have yields between 0.016 and 0.007, all of which are reduced with respect to the parent compound HPDME (0.09). Global analysis of the transient fluorescence decays of the dyads and triads requires two exponential components (˜5–6ns and ˜1–2ns) to fit the data, while a single exponential component with a lifetime of 9.3 ns describes the decay data of the parent HPDME. Possible mechanisms for the observed porphyrin fluorescence quenching by the nearby carotenoid are discussed. Nanosecond transient absorption reveals a carotene triplet with maximum absorption at 560 nm and a 5.0 μs lifetime. No transient was detected at 450 nm, indicating rapid (10 ns) triplet energy transfer from the hematoporphyrin to the carotenoid moieties in fluid as well as in rigid media. The yield of triplet energy transfer from the porphyrin to the carotenoid moiety is unity. Singlet oxygen, O2(1δg), studies support the transient absorption data, as none of these compounds is capable of sensitizing O2(1δg). Liposome vesicles were used to study the photophysical characteristics of the dyes in phospholipid membranes. Singlet oxygen was not sensitized by the dyads and triads in liposomes. Transient absorption measurements suggest that the triads are substantially aggregated within the phospholipid bilayer, whereas aggregation in the dyads is less severe.

Model systems for observing photoredox reactions of carotenoids

Abstract