Photoinduced electron transfer of chlorophyll in lipid bilayer system

Photoinduced electron transfer from chlorophyll-a throughtheinterface of dipalmitoylphosphatidylcholine (DPPC) headgroup of the lipid bilayers was studied with electron magnetic resonance (EMR). The photoproduced radicals were identified with electron spin resonance (ESR) and radical yields of chlorophyll-a were determined by double integration ESR spectra. The formation of vesicles was identified by changes in measured λ_max values from diethyl ether solutions to vesicles solutions indirectly, and observed directly with SEM and TEM images. The efficiency of photosynthesis in model system was determined by measuring the amount of chlorophyll-a radical yields which were obtained from integration of ESRspectra.     

Photoinduced Electron Transfer in an Amine–Corrole–Perylene Bisimide Assembly: Charge Separation over Terminal Components Favoured by Solvent Polarity

An assembly has been synthesised that consists of four units: a meso‐substituted corrole (C3), perylene bisimide (PI), and two electron‐rich triphenylamine (DPA) units. PI is connected through a 1,4‐phenylene bridge to C3, whereas the two DPA units are linked to C3 through a diphenyl ether linkage, which is used for the first time to connect the various moieties. Various synthetic strategies were elaborated, and the chosen one afforded the final system in six steps in an overall yield of 6 %. The resulting assembly, made of three different units, was named a “triad”. Excitation of the corrole (C3) or perylene bisimide (PI) units led to the charge‐separated state DPA‐C3⁺‐PI^? with a rate k>10¹¹ s^?1 in benzonitrile and dichloromethane (CH₂Cl₂) or with k of the order of 10¹⁰ s^?1 in toluene. The latter charge‐separated state decayed to the ground state with a rate k=1.8×10⁹ s^?1 in toluene. In the polar solvents benzonitrile and dichloromethane, recombination to the ground state competes with a charge shift to form the distal charge‐separated state, DPA⁺‐C3‐PI^?, the formation of which occurs with a yield of 50 %. Recombination to the ground state of DPA⁺‐C3‐PI^? occurs with a rate k=5×10⁷ s^?1 in CH₂Cl₂ and k=2×10⁷ s^?1 in benzonitrile.     

Remarkable Dependence of the Final Charge Separation Efficiency on the Donor–Acceptor Interaction in Photoinduced Electron Transfer

The unprecedented dependence of final charge separation efficiency as a function of donor–acceptor interaction in covalently‐linked molecules with a rectilinear rigid oligo‐p‐xylene bridge has been observed. Optimization of the donor–acceptor electronic coupling remarkably inhibits the undesirable rapid decay of the singlet charge‐separated state to the ground state, yielding the final long‐lived, triplet charge‐separated state with circa 100 % efficiency. This finding is extremely useful for the rational design of artificial photosynthesis and organic photovoltaic cells toward efficient solar energy conversion.     

Intramolecular Charge Transfer‐Enhanced BODIPY Photosensitizer in Photoinduced Electron Transfer and Its Application to Photoxidation under Mild Condition

Photoinduced electron transfer process is a crucial step in photooxidation to obtain synthetic chemicals. However, the driving forces of electron transfer as priority in all have been rarely studied in stepwise detail. Herein, we report a series of BODIPY derivatives with an emphasis on the intramolecular charge transfer, enhancing the key step of photoinduced electron transfer process and photooxidation performances. A series of novel BODIPY photosensitizers ( B‐1 – B‐5 ) were prepared, wherein diethylamine amino of B‐3 as charge injection group was conjugated to the 2,6‐diiodo‐styryl‐BODIPY, and the electron transfer impetus was enhanced 1.6 times due to its more negative redox potentials. These results were also confirmed by the DFT/TDDFT calculation. Without pure oxygen, B‐3 still can exhibit an exceptional performance in photoxidative aromatization of 1,4‐DHP under mild condition. After irradiation for 28 min, the conversion rate came to 98.2%.     

Charge-Transfer in Panchromatic Porphyrin-Tetracyanobuta-1,3-Diene-Donor Conjugates: Switching the Role of Porphyrin in the Charge Separation Process

Using a combination of cycloaddition-retroelectrocyclization reaction, free-base and zinc porphyrins (H₂P and ZnP) are decorated at their β-pyrrole positions with strong charge transfer complexes, viz., tetracyanobuta-1,3-diene (TCBD)-phenothiazine ( 3 and 4 ) or TCBD-aniline ( 7 and 8 ), novel class of push-pull systems. The physico-chemical properties of these compounds (MP-Donor and MP-TCBD-Donor) have been investigated using a range of electrochemical, spectroelectrochemical, DFT as well as steady-state and time-resolved spectroscopic techniques. Ground-state charge transfer interactions between the porphyrin and the electron-withdrawing TCBD directly attached to the porphyrin π-system extended the absorption features well into the near-infrared region. To visualize the photo-events, energy level diagrams with the help of free-energy calculations have been established. Switching the role of porphyrin from the initial electron acceptor to electron donor was possible to envision. Occurrence of photoinduced charge separation has been established by complementary transient absorption spectral studies followed by global and target data analyses. Better charge stabilization in H₂P derived over ZnP derived conjugates, and in phenothiazine derived over aniline derived conjugates has been possible to establish. These findings highlight the importance of the nature of porphyrins and second electron donor in governing the ground and excited state charge transfer events in closely positioned donor-acceptor conjugates.     

Photoinduced Charge Separation in a Donor–Spacer–Acceptor Dyad with N‐Annulated Perylene Donor and Methylviologen Acceptor

The first donor–acceptor species in which a strongly emissive N‐annulated perylene dye is connected to a methylviologen electron acceptor unit via its macrocyclic nitrogen atom, is prepared by a stepwise, modular procedure. The absorption spectra, redox behavior, spectroelectrochemistry and photophysical properties of this dyad and of its model species are investigated, also by pump–probe fs transient absorption spectroscopy. Photoinduced oxidative electron transfer from the excited state of the dyad, centered on the N‐annulated perylene subunit, to the appended methyviologen electron acceptor takes place in a few ps. The charge‐separated species recombines in 19 ps. Our results indicate that N‐annulated perylene can be connected to functional units by taking advantage of the macrocyclic nitrogen, an option never used until now, without losing their properties, so opening the way to new designing approaches.     

Photoinduced Intramolecular Charge Transfer in Donor-acceptor Dyad and Donor-bridge-acceptor Triad

The ground and excited state properties of the 60fullerene, diphenylbenzothiadiazole-triphenylamine (PBTDP-TPA) dyad and fullerene-diphenylbenzothiadiazole-triphenylamine (fullerene-PBTDP-TPA) triad were investigated theoretically using density functional theory with B3LYP functional and 3-21G basis et and time-dependent density functional theory with B3LYP functional and STO-3G basis set as well as 2D and 3D real space analysis methods. The 2D site representation reveals the electron-hole coherence on excitation. The 3D transition density shows the orientation and strength of the transition dipole moment, and the 3D charge difference density gives the orientation and result of the intramolecular charge transfer. Also, photoinduced intermolecular charge transfer (ICT) in PBTDP-TPA-fullerene triad are identified with 2D and 3D representations, which reveals the mechanisms of ICT in donor-bridge-acceptor triad on excitation. Besides that we also found that the direct superexchange ICT from donor to acceptor (tunneling through the bridge) strongly promotes the ICT in the donor-bridge-acceptor triad.     

Improving the Photoinduced Charge Separation Parameters in Corrole–Perylene Carboximide Dyads by Tuning the Redox and Spectroscopic Properties of the Components

A couple of corrole–perylene carboximide dyads ( C2‐PIa and C2‐PIx ) have been synthesized and their photoreactivity has been evaluated. We aimed at obtaining better performances for photoinduced charge separation, both in terms of efficiency and in terms of lifetime, with respect to formerly studied systems. The energy level of the charge‐separated state was tuned by selecting perylene and corrole components with diverse redox and spectroscopic properties. High spectroscopic energy levels of the perylene carboximide derivatives (PIs) allow a fast charge separation to be maintained in competition with an energy‐transfer process from the PI to the corrole unit. Yields and lifetimes of charge separation in toluene are, respectively, 75 % and 2.5 μs for C2‐PIa and 65 % and 24 ns for C2‐PIx . The results and the effect of solvent polarity are discussed in the framework of current energy‐ and electron‐transfer theories.     

Unambiguous Diagnosis of Photoinduced Charge Carrier Signatures in a Stoichiometrically Controlled Semiconducting Polymer‐Wrapped Carbon Nanotube Assembly

Single‐walled carbon nanotube (SWNT)‐based nanohybrid compositions based on (6,5) chirality‐enriched SWNTs ([(6,5) SWNTs]) and a chiral n‐type polymer (S‐PBN(b)‐Ph₄PDI) that exploits a perylenediimide (PDI)‐containing repeat unit are reported; S‐PBN(b)‐Ph₄PDI‐[(6,5) SWNT] superstructures feature a PDI electron acceptor unit positioned at 3 nm intervals along the nanotube surface, thus controlling rigorously SWNT–electron acceptor stoichiometry and organization. Potentiometric studies and redox‐titration experiments determine driving forces for photoinduced charge separation (CS) and thermal charge recombination (CR) reactions, as well as spectroscopic signatures of SWNT hole polaron and PDI radical anion (PDI^?.) states. Time‐resolved pump–probe spectroscopic studies demonstrate that S‐PBN(b)‐Ph₄PDI‐[(6,5) SWNT] electronic excitation generates PDI^?. via a photoinduced CS reaction (τ_CS≈0.4 ps, Φ_CS≈0.97). These experiments highlight the concomitant rise and decay of transient absorption spectroscopic signatures characteristic of the SWNT hole polaron and PDI^?. states. Multiwavelength global analysis of these data provide two charge‐recombination time constants (τ_CR≈31.8 and 250 ps) that likely reflect CR dynamics involving both an intimately associated SWNT hole polaron and PDI^?. charge‐separated state, and a related charge‐separated state involving PDI^?. and a hole polaron site produced via hole migration along the SWNT backbone that occurs over this timescale.     

Effect on Charge Transfer and Charge Recombination by Insertion of a Naphthalene‐Based Bridge in Molecular Dyads Based on Borondipyrromethene (Bodipy)

The photophysical properties of two related dyads based on a N,N‐dimethylaniline donor coupled to a fully‐alkylated boron dipyrromethene (Bodipy) acceptor are described. In one dyad, BD1 , the donor unit is attached directly to the Bodipy group, whereas in the second dyad, BD2 , a naphthalene spacer separates the two units. Cyclic voltammograms recorded for the two dyads in deoxygenated MeCN containing a background electrolyte are consistent with the reversible one‐electron oxidation of the N,N‐dimethylaniline group and the reversible one‐electron reduction of the Bodipy nucleus. There is a reasonable driving force (ΔG_CT) for photoinduced charge transfer from the N,N‐dimethylaniline to the Bodipy segment in MeCN. The charge‐transfer state is formed for BD1 extremely fast (1.5 ps), but decays over 140 ps to partially restore the ground state. On the other hand, the charge‐transfer state for BD2 is formed more slowly, but it decays extremely rapidly. Charge recombination for both dyads leads to a partial triplet formation on the Bodipy group. The naphthalene spacer group is extremely efficient at promoting back electron transfer.     

Light‐Driven Charge Separation in Isoxazolidine–Perylene Bisimide Dyads

A series of arrays for light‐driven charge separation is presented, in which perylene tetracarboxylic bisimide is the light‐absorbing chromophore and electron acceptor, whereas isoxazolidines are colourless electron donors, the electron‐releasing properties of which are increased with respect to the amino group by means of the α‐effect. Charge separation (CS) in toluene over a distance ranging from ≈10 to ≈16 Å, with efficiencies of ≈95 to ≈50 % and CS lifetimes from 300 ps to 15 ns, are demonstrated. In dichloromethane the charge recombination reaction is faster than charge separation, preventing accumulation of the CS state. The effects of solvent polarity and molecular structure are discussed in the frame of current theories.     

Photosynthetic Antenna‐Reaction Center Mimicry with a Covalently Linked Monostyryl Boron‐Dipyrromethene–Aza‐Boron‐Dipyrromethene–C60 Triad

An efficient functional mimic of the photosynthetic antenna‐reaction center has been designed and synthesized. The model contains a near‐infrared‐absorbing aza‐boron‐dipyrromethene (ADP) that is connected to a monostyryl boron‐dipyrromethene (BDP) by a click reaction and to a fullerene (C₆₀) using the Prato reaction. The intramolecular photoinduced energy and electron‐transfer processes of this triad as well as the corresponding dyads BDP‐ADP and ADP‐C₆₀ have been studied with steady‐state and time‐resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge‐separated states. Such calculations show that electron transfer from the singlet excited ADP (¹ADP*) to C₆₀ yielding ADP^.+‐C₆₀^.? is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from ¹BDP* to ADP in the dyad BDP‐ADP and electron transfer from ¹ADP* to C₆₀ in the dyad ADP‐C₆₀. Sequential energy and electron transfer have also been clearly observed in the triad BDP‐ADP‐C₆₀. By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10¹¹ s^?1). The dynamics of electron transfer through ¹ADP* has also been studied by monitoring the formation of C₆₀ radical anion at 1000 nm. A fast charge‐separation process from ¹ADP* to C₆₀ has been detected, which gives the relatively long‐lived BDP‐ADP^.+C₆₀^.? with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge‐separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP‐ADP and ADP‐C₆₀, and the triad BDP‐ADP‐C₆₀ are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems.     

Ultrafast Photoinduced Charge Separation in Wide‐Band‐Capturing Self‐Assembled Supramolecular Bis(donor styryl)BODIPY–Fullerene Conjugates

A new series of self‐assembled supramolecular donor–acceptor conjugates capable of wide‐band capture, and exhibiting photoinduced charge separation have been designed, synthesized and characterized using various techniques as artificial photosynthetic mimics. The donor host systems comprise of a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) containing a crown ether entity at the meso‐position and two styryl entities on the pyrrole rings. The styryl end groups also carried additional donor (triphenylamine or phenothiazine) entities. The acceptor host system was a fulleropyrrolidine comprised of an ethylammonium cation. Owing to the presence of extended conjugation and multiple chromophore entities, the BODIPY host revealed absorbance and emission well into the near‐IR region covering the 300–850 nm spectral range. The donor–acceptor conjugates formed by crown ether–alkyl ammonium cation binding of the host–guest system was characterized by optical absorbance and emission, computational, and electrochemical techniques. Experimentally determined binding constants were in the range of 1–2×10⁵ M ^?1. An energy‐level diagram to visualize different photochemical events was established using redox, computational, absorbance, and emission data. Spectral evidence for the occurrence of photoinduced charge separation in these conjugates was established from femtosecond transient absorption studies. The measured rates indicated ultrafast charge separation and relatively slow charge recombination revealing their usefulness in light‐energy harvesting and optoelectronic device applications. The bis(donor styryl)BODIPY‐derived conjugates populated their triplet excited states during charge recombination.     

Conformational Dynamics of Monomer‐ versus Dimer‐like Features in a Naphthalenediimide‐Based Conjugated Cyclophane

The design and synthesis of an enantiomeric pair of 1,8‐diethynylanthracene‐bridged naphthalenediimide (NDI)‐based cyclophanes ( Cyclo‐NDI s) are reported. Each enantiomer of Cyclo‐NDI exhibits a circularly polarized luminescence signal with a relatively large luminescence dissymmetry factor (g_lum=±8×10^?3). We have further investigated the modulation of through‐space electronic communication between co‐facially oriented NDIs in a discrete Cyclo‐NDI with changes in the temperature. Tuning of the electronic communication results from the conformational transformation of monomer‐ versus dimer‐like features of Cyclo‐NDI , as confirmed by UV/Vis, fluorescence, circular dichroic, and NMR spectroscopic analysis. The temperature‐dependent optical response in the Cyclo‐NDI through the conformational transformation could be utilized as a highly sensitive and reversible optical thermometer in a wide temperature range (100 to ?80 °C).     

Evidence of Photoinduced Charge Separation in the Metal–Organic Framework MIL‐125(Ti)‐NH2

Herein, we describe the photochemical behavior of the porous metal–organic framework MIL‐125(Ti)‐NH₂, built up from cyclic Ti₈O₈(OH)₄ oxoclusters and 2‐aminoterephthalate ligands. While MIL‐125(Ti)‐NH₂ does not emit upon excitation at 420 nm, laser flash photolyses of dry samples (diffuse reflectance) or aqueous suspensions (transmission) of the solid have allowed detecting a transient characterized by a continuous absorption from 390 to 820 nm decaying in the sub‐millisecond timescale, which is quenched by oxygen. This transient has been attributed to the charge‐separation state. Firm evidence for this assignment was obtained by lamp irradiation of aqueous suspensions of MIL‐125(Ti)‐NH₂ in the presence of electron‐donor (N,N,N′N′‐tetramethyl‐p‐phenylenediamine) or electron‐acceptor (methylviologen) probe molecules, which has allowed the visual detection of the corresponding radical ions, in agreement with the occurrence of photoinduced charge separation in MIL‐125(Ti)‐NH₂.     

Stimuli‐Responsive Reversible Fluorescence Switching in a Crystalline Donor–Acceptor Mixture Film: Mixed Stack Charge‐Transfer Emission versus Segregated Stack Monomer Emission

We report on a molecularly tailored 1:1 donor–acceptor (D‐A) charge‐transfer (CT) cocrystal that manifests strongly red‐shifted CT luminescence characteristics, as well as noteworthy reconfigurable self‐assembling behaviors. A loosely packed molecular organization is obtained as a consequence of the noncentrosymmetric chemical structure of molecule A1 , which gives rise to considerable free volume and weak intermolecular interactions. The stacking features of the CT complex result in an external stimuli‐responsive molecular stacking reorganization between the mixed and demixed phases of the D‐A pair. Accordingly, high‐contrast fluorescence switching (red?blue) is realized on the basis of the strong alternation of the electronic properties between the mixed and demixed phases. A combination of structural, spectroscopic, and computational studies reveal the underlying mechanism of this stimuli‐responsive behavior.     

环双(百草枯对苯撑)-双2-萘甲酸三缩四乙二醇酯二元超分子给受体体系光诱导电子转移研究

本文利用核磁氢谱、吸收光谱和荧光光谱证明了环双(百草枯对苯撑)(CBPQT)与双2-萘甲酸三缩四乙二醇(N-P₄-N)在乙腈溶液中能够形成1:1的二元超分子给受体体系.瞬态吸收光谱的研究表明该超分子体系中光诱导电子转移的速率k_CS>1.0×10⁸s^-1,电子回传的速率k_CR=1.26×10³s^-1,光诱导电子转移所生成电荷分离态的寿命长达794μs.     

Mechanism of Back Electron Transfer in an Intermolecular Photoinduced Electron Transfer Reaction: Solvent as a Charge Mediator

Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine the BET reaction of pyrene (Py) and 1,4‐dicyanobenzene (DCB) in acetonitrile (ACN) by using time‐resolved near‐ and mid‐IR spectroscopy. The Py dimer radical cation (Py₂^.+) and DCB radical anion (DCB^.?) generated after photoexcitation of Py show asynchronous decay kinetics. To account for this observation, we propose a reaction mechanism that involves electron transfer from DCB^.? to the solvent and charge recombination between the resulting ACN dimer anion and Py₂^.+. The unique role of ACN as a charge mediator revealed herein could have implications for strategies that retard charge recombination in dye‐sensitized solar cells.     

表面电性可控的磁性微球的制备、表征及其在基因组DNA萃取中的应用

运用水热法、St?ber法制备了具有核壳型结构的超顺磁性Fe3 O4@SiO2微球,运用氨丙基三乙氧基硅烷( APTES)对Fe3 O4@SiO2微球表面进行修饰,得到表面电性可控的氨基化Fe3 O4@SiO2磁性微球,运用透射、扫描电镜表征微球形貌,采用Zeta电位研究微球表面的荷电特性。将氨基化Fe3 O4@SiO2微球用于人类全血中基因组脱氧核糖核酸( DNA)的萃取,开发了固相萃取方法,并探究微球与DNA的作用机理,对提取产物进行凝胶电泳和PCR实验。结果表明,自制的微球成功地从全血中提取出纯度较高的基因组DNA,提取率约70%,微球对基因组DNA的饱和吸附量约为40 ng/μg,提取液可直接用于进一步的生物分析。