Light-harvesting Units Research Articles

Tuning Photoinduced Electron Transfer in POM-Bodipy Hybrids by Controlling the Environment: Experiment and Theory.

The optical and electrochemical properties of a series of polyoxometalate (POM) oxoclusters decorated with two bodipy (boron-dipyrromethene) light-harvesting units were examined. Evaluated here in this polyanionic donor-acceptor system is the effect of the solvent and associated counterions on the intramolecular photoinduced electron transfer. The results show that both solvents and counterions have a major impact upon the energy of the charge-transfer state by modifying the solvation shell around the POMs. This modification leads to a significantly shorter charge separation time in the case of smaller counterion and slower charge recombination in a less polar solvent. These results were rationalized in terms of Marcus theory and show that solvent and counterion both affect the driving force for photoinduced electron transfer and the reorganization energy. This was corroborated with theoretical investigations combining DFT and molecular dynamics simulations.

A Nano-Enzymatic Photoelectrochemical L-Cysteine Biosensor Based on Bi2MoO6 Modified Honeycomb TiO2 Nanotube Arrays Composite

Improving light harvesting behavior and recognition sites of sensor is an effective way to achieve highly sensitive and selective detection of nano-enzymatic photoelectrochemical (PEC) L-cysteine (Cyst). In this work, the Bi2MoO6-TiO2 composite (BMO-HTNTs) with honeycomb TiO2 nanotube arrays (HTNTs) as light harvesting unit and Bi2MoO6 nanoparticles (BMO) as recognition unit was prepared. The typical honeycomb-nanoparticle heterostructure between HTNTs and BMO improves the separation efficiency of the electron-hole pairs. Moreover, BMO nanoparticles fully dispersed on HTNTs with large specific surface area provide more sites for Cyst recognition. The composite exhibited the enhanced light absorption and higher photocurrent density at 0.2 V (vs. Ag/AgCl), which was 4 times than that of HTNTs under simulated light. Ingeniously, Cyst can not only be specifically recognized through the Bi-S bonds but also act as electron donor to scavenge the photogenerated holes of BMO-HTNTs, resulting in the increase of PEC responses. The PEC sensor showed superior analytical performance for Cyst detection with two linear regression equations in the range of 500 nM to 500 μM and a detection limit of 150 nM. The results of the enzyme-free sensor on practical urine and serum samples demonstrated its promising application in biological monitoring.

Colocalization of light harvesting and catalytic units in a ‘soft’ coordination polymer hydrogel toward visible-light driven photocatalytic hydrogen production

An anthracene based coordination polymer gel (CPG) material has been prepared which acted as a stable visible light driven photocatalyst without adding any co-catalyst for hydrogen evolution from water with the maximum rate of 0.97 mmol g−1 h−1.

Visible-light-driven CO2 reduction with g-C3N4-based composite: Enhancing the activity of manganese catalysts

A heterogeneous photocatalytic system that consists of a manganese complex and g-C3N4, which mainly act as the catalytic and light-harvesting units, respectively, was developed for the reduction of CO2 to CO. The anchoring group (carboxyl) and the structure of g-C3N4 promote electron transfer from g-C3N4 to the manganese unit and strengthen electronic interactions between the two units. The photocatalytic properties and stability of a tricarbonyl Mn bipyridyl complex were significantly enhanced by anchoring on a g-C3N4 support. The turnover number for CO formation reached 75.7 under the optimal reaction conditions. This photocatalytic system is environmentally friendly and sustainable, and will stimulate the development of potential photocatalytic CO2 transformation methods that use solar energy.

Steady-State Analysis of Light-Harvesting Energy Transfer Driven by Incoherent Light: From Dimers to Networks.

The question of how quantum coherence facilitates energy transfer has been intensively debated in the scientific community. Since natural and artificial light-harvesting units operate under the stationary condition, we address this question via a nonequilibrium steady-state analysis of a molecular dimer irradiated by incoherent sunlight and then generalize the key predictions to arbitrarily complex exciton networks. The central result of the steady-state analysis is the coherence-flux-efficiency relation: η = c∑i≠jFijκj = 2c∑i≠jJijIm[ρij]κj, where c is the normalization constant. In this relation, the first equality indicates that the energy transfer efficiency, η, is uniquely determined by the trapping flux, which is the product of the flux, F, and branching ratio, κ, for trapping at the reaction centers, and the second equality indicates that the energy transfer flux, F, is equivalent to the quantum coherence measured by the imaginary part of the off-diagonal density matrix, that is, Fij = 2JijIm[ρij]. Consequently, maximal steady-state coherence gives rise to optimal efficiency. The coherence-flux-efficiency relation holds rigorously and generally for any exciton network of arbitrary connectivity under the stationary condition and is not limited to incoherent radiation or incoherent pumping. For light-harvesting systems under incoherent light, the nonequilibrium energy transfer flux (i.e., steady-state coherence) is driven by the breakdown of detailed balance and by the quantum interference of light excitations and leads to the optimization of energy transfer efficiency. It should be noted that the steady-state coherence or, equivalently, efficiency is the combined result of light-induced transient coherence, inhomogeneous depletion, and the system-bath correlation and is thus not necessarily correlated with quantum beatings. These findings are generally applicable to quantum networks and have implications for quantum optics and devices.

Construction of TiO2 nanosheets/tetra (4-carboxyphenyl) porphyrin hybrids for efficient visible-light photoreduction of CO2

The design and construction of photocatalysts in converting CO2 into value-added chemicals is of significant importance for addressing energy shortages and environmental pollution problems. In this work, a TiO2 nanosheets/tetra (4-carboxyphenyl) porphyrin (TiO2 NSs/TCPP) hybrid for photoreduction of CO2 was developed using a simple self-assemble approach. The TCPP works as the light-harvesting unit to generate light-induced electron-hole pairs, with the connection between the TCPP and TiO2 facilitating the electron injection to the CB of TiO2 as well as inhibiting the recombination of photo-generated electron-hole pairs, then the highly active (0 0 1) facets of TiO2 NSs serve as the reaction sites and efficiently convert the CO2 molecules adsorbed on the surface of the catalysts into CO and CH4 products. The influence of TCPP content on the photocatalytic activity was investigated. Compared to the pristine TiO2 NSs material, the TiO2 NSs/11.5% TCPP composite displayed a much-enhanced photocatalytic CO2 reduction activity, which is equal to 37-fold enhancements in the CO evolution rate. Furthermore, a possible mechanism for CO2 photoreduction over TiO2 NSs/TCPP hybrids is proposed on the basis of the photocatalytic and photo(electro)chemical results.

Luminescent properties of newly synthesized thioxanthone-polypyridyl derivatives and their metal-organic complexes

Thioxanthones (TXs) are not only important photoinitiators for free radical polymerization but also efficient light-harvesting units for organic light emitting diodes. Here, we reported synthesis and photophysical properties of new TXs with 2,2′-bipyridyl (BPy) and 2,2':6′,2″-terpyridyl (TPy) substituents, TXOBPy and TXOTPy, as well as those of their complexes with some transition metal ion (Zn2+, Fe2+, Ni2+, Eu3+ and Tb3+) solution in diverse solvents and solid powders. Absorption spectra revealed mainly two groups of bands at approximately 250–290 and 366 nm, attributed to the π–π* and n–π* electron transfer of the TXs. A broad luminescent emission was recorded and centered at approximately 422 nm for these TXs and their metal complexes, its relative intensity was solvent and concentration dependent. Further, it was observed that this emission band red shifted to approximately 470 nm in their solid powders. For the TXs and their Zn/Fe/Ni-complexes in the methanol solutions, the quantum efficiency (QE) of TX rings was about 0.04–0.11, and the fluorescent lifetime (τ) was about 0.5–1.2 ns. On the other hand, for the Fe and Ln-complexes, the QE of TX rings was below 0.01, which was attributed to the reason that the excited energy of the TX rings was quenched by ligand-Fe2+ charge transfer or by transferring the energy to the central Ln3+ (Eu3+ and Tb3+) ions. Thus, the Ln-TXOBPy and Ln-TXOTPy complexes gave off strong and sharp Eu3+/Tb3+ emissions at the wavelengths between 480 and 750 nm. The fluorescent emission lifetime of the central Ln3+ ions was about 0.3–0.6 ms. Thus, we can suggest that the TXOBPy and TXOTPy photoinitiators can act as potential candidates for the development of efficient emitters with tunable light emissions and luminescent sensors.

Semiconducting Polymer Nanobiocatalysts for Photoactivation of Intracellular Redox Reactions.

An organic semiconducting polymer nanobiocatalyst (SPNB) composed of a semiconducting polymer core conjugated with microsomal cytochrome P450 (CYP) has been developed for photoactivation of intracellular redox. The core serves as the light-harvesting unit to initiate photoinduced electron transfer (PET) and facilitate the regeneration of dihydronicotinamide adenine dinucleotide phosphate (NADPH), while CYP is the catalytic center for intracellular redox. Under light irradiation, the semiconducting core can efficiently catalyze the generation of NADPH with a turnover frequency (TOF) 75 times higher than the reported nanosystems, ensuring the supply of the cofactor for intracellular redox. SPNB-mediated intracellular redox thus can be efficiently activated by light in living cells to convert the model substrate and also to trigger the bioactivation of anticancer drugs. This study provides an organic nanobiocatalytic system that allows light to remotely control intracellular redox in living systems.

Predictive modeling of broad wavelength light-harvesting performance in assemblies of multiple chromophores

Developing efficient panchromatic light harvesting systems that exploit the energy available from the entire solar spectrum in an economically feasible and scalable fashion is of great importance. Light harvesting by incorporating multiple chromophores into molecular assemblies such as micelles and vesicles is one method for accomplishing this result. In this paper, we describe panchromatic light harvesting in lipid-based vesicle bilayers that contain a random distribution of lipid-bound chromophores. Numerically exact modeling based on Förster theory is developed to establish the criteria for designing a highly efficient panchromatic light-harvesting unit. An approximate modeling method is also developed to greatly reduce the complexity of the modeling problem. Both the exact and approximate models are verified by designing and experimentally testing an efficient three-chromophore light-harvesting system. For the experiments, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(lissamine rhodamine B sulfonyl) (Rhod) as the lowest energy chromophore, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl) (NBD) as an intermediate acceptor, and Marina Blue® 1,2-Dihexadecanoyl-sn-Glycero-3-Phosphoethanolamine (MB) as the highest energy absorber (donor) are selected. From chromophore concentrations and R0 values, modeling predicts an overall efficiency of energy transfer to the terminal acceptor greater than ≈0.6 across a broad excitation wavelength range of ≈250 nm. The predicted transfer efficiency is verified by the experimental results. In addition, comparison of the approximate modeling method with both the numerically exact method and experimental results confirms that the computationally efficient approximate method is sufficiently accurate to guide choices of experimental parameters such as chromophore concentration. Overall, these results show predictive design of panchromatic light-harvesting performance can be performed rapidly and efficiently using an approximate kinetic model for randomly distributed assemblies of multiple chromophores.

Visible light active 2D C3N4-CdS hetero-junction photocatalyst for effective removal of azo dye by photodegradation

A hetero-junction two dimensional photocatalyst that consists of organic semiconductor carbon nitride (C3N4) and inorganic semiconductor CdS, which acts as the light harvesting units and heterogeneous catalyst, was developed for the degradation of azo dye methyl orange (MO). Both materials are visible light active semiconductor. So the effective band gap of this heterojunction materials does not significantly change the visible light activity, but the injection of electrons from excited C3N4 to CdS increases the stability of hole-electron pair and that ultimately enhances the photocatalytic activity. This heterojunction catalyst finally can remove 97% of dyes and that is comparatively higher than individual pure materials. Finally, by using DFT analysis the band structure and the level diagrams of this photocatalyst are also analyzed.

Cryospectroscopy Studies of Intact Light-Harvesting Antennas Reveal Empirical Electronic Energy Transitions in Two Cyanobacteria Species

Understanding of electronic energy transition (EET) mechanisms from the light-harvesting unit to the reaction center in a natural system has been limited by (a) the use of conventional transient time-resolved spectroscopy at room temperature, which result in high signal-to-noise ratio and (b) examining extracts instead of intact light-harvesting units. Here, we report previously unknown differences and new insight in EET of two cyanobacteria species, Acaryochloris marina and Thermosynechoccocus vulcanus, which have been found only after using UV-vis, hole-burning, and fluorescence spectroscopy at ultralow temperature and examining their intact light-harvesting unit, phycobilisomes (PBS). Although the exciton formation is similarly induced by photoexcitation of chromophore assemblies in phycocyanin (PC) and allophycocyanin (APC) in PBSs of both species, the EET mechanisms are totally different, being adiabatic in A. marina and nonadiabatic in T. vulcanus. The PBS of A. marina has only one APC trimer and energy transfer is through coupling of α84 in APC with β84 in adjacent PC. In T. vulcanus, the PBS has three components: coupling between APC core and the entire PC rod and couplings of β-β18 and of LCM to β in the adjacent APC-like trimer. A total of 80% of the excitation energy is trapped in the coupling β-β18 and regulates the flow of energy from the high- to low-level terminal electronic transition emitter β-LCM. All these details cannot be observed at room temperature and in extracted units.

Quantum Redirection of Antenna Absorption to Photosynthetic Reaction Centers.

The early steps of photosynthesis involve the photoexcitation of reaction centers (RCs) and light-harvesting (LH) units. Here, we show that the historically overlooked excitonic delocalization across RC and LH pigments results in a redistribution of absorption amplitudes that benefits the absorption cross section of the optical bands associated with the RC of several species. While we prove that this redistribution is robust to the microscopic details of the dephasing between these units in the purple bacterium Rhodospirillum rubrum, we are able to show that the redistribution witnesses a more fragile, but persistent, coherent population dynamics which directs excitations from the LH toward the RC units under incoherent illumination and physiological conditions. Even though the redirection does not seem to affect importantly the overall efficiency in photosynthesis, stochastic optimization allows us to delineate clear guidelines and develop simple analytic expressions in order to amplify the coherent redirection in artificial nanostructures.

Directly Coupled Versus Spectator Linkers on Diimine PtII Acetylides-Change the Structure, Keep the Function?

Modification of light-harvesting units with anchoring groups for surface attachment often compromises light-harnessing properties. Herein, a series of [donor-acceptor-anchor] platinum(II) diimine (bis-)acetylides was developed in order to systematically compare the effect of conjugated versus electronically decoupled modes of attachment of protected anchoring groups on the photophysical properties of light-harvesting units. The first examples of "decoupled" phosphonate diimine PtII complexes are reported, and their properties are compared and contrasted to those of carboxylate analogues studied by a diversity of methods. Ultrafast time-resolved IR and transient absorption spectroscopy revealed that all complexes have a charge-transfer (CT) lowest excited state with lifetimes between 2 and 14 ns. Vibrational signatures and dynamics of CT states were identified; the assignment of electronic states and their vibrational origin was aided by TDDFT calculations. Ultrafast energy redistribution accompanied by structural changes was directly captured in the CT states. A significant difference between the structures of the electronic ground and CT excited states, as well as differences in the structural reorganisation in the complexes bearing directly attached or electronically decoupled anchoring groups, was discovered. This work demonstrates that decoupling of the anchoring group from the light-harvesting core by a saturated spacer is an easy approach to combine surface attachment with high reduction potential and ten times longer lifetime of the CT excited state of the light-absorbing unit, and retain electron-transfer photoreactivity essential for light-harvesting applications.

Mapping the ultrafast flow of harvested solar energy in living photosynthetic cells

Photosynthesis transfers energy efficiently through a series of antenna complexes to the reaction center where charge separation occurs. Energy transfer in vivo is primarily monitored by measuring fluorescence signals from the small fraction of excitations that fail to result in charge separation. Here, we use two-dimensional electronic spectroscopy to follow the entire energy transfer process in a thriving culture of the purple bacteria, Rhodobacter sphaeroides. By removing contributions from scattered light, we extract the dynamics of energy transfer through the dense network of antenna complexes and into the reaction center. Simulations demonstrate that these dynamics constrain the membrane organization into small pools of core antenna complexes that rapidly trap energy absorbed by surrounding peripheral antenna complexes. The rapid trapping and limited back transfer of these excitations lead to transfer efficiencies of 83% and a small functional light-harvesting unit.

Palladium-directed self-assembly of multi-titanium(IV)-porphyrin arrays on the substrate surface as sensitive ultrathin films for hydrogen peroxide sensing, photocurrent generation, and photochromism of viologen

Multiporphyrin arrays are large, π-conjugated chromophores with high absorption efficiency and strong chemical stability that play an important role in supramolecular and advanced material sciences. Palladium-directed self-assembly of multiporphyrin array ultrathin films was achieved on substrate surfaces using oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium (IV) complex [TiO(TPyP)] as a linker and sodium tetrachloropalladate (Na2PdCl4) as a connector. The Pd-TiOTPyP films as prepared were characterized by using UV–vis absorption and X-ray photoelectron spectroscopy, as well as by atomic force and scanning electron microscopy. The Soret absorption band of TiOTPyP was observed to red shift by 6nm when the Pd-TiOTPyP multilayer-modified quartz substrate was immersed in an aqueous solution containing hydrogen peroxide. This was attributed to the formation of a TiO2TPyP monoperoxo complex. This oxidation reaction could be accelerated in an acidic solution. Furthermore, the immobilized Pd-TiOTPyP multilayers could act as light-harvesting units for photocurrent generation and photochromism of viologens, with strong stability, reproducibility, and recyclability. The photocurrent density could be enhanced in electrolyte solutions containing electron donors such as triethanolamine, or electron acceptors such as viologens. Finally, photoinduced reduction (photochromism) of viologens was investigated using the Pd-TiOTPyP multilayers as light sensitizers and EDTA as the electron donors.

Aggregation-Induced Energy Transfer in a Decanuclear Os(II)/Ru(II) Polypyridine Light-Harvesting Antenna Dendrimer

Summary Self-assembly of light-harvesting antenna (multichromophoric) systems is a typical feature of natural photosynthetic organisms, aimed at maximizing light absorption and solar energy conversion. Inspired by this concept, self-assembly strategies for integrating light-harvesting units are highly desirable objectives in supramolecular chemistry. Here, we demonstrate that self-assembly of light-harvesting dendrimers based on Ru(II) and Os(II) polypyridine complexes leads to aggregation-induced energy transfer. This phenomenon is proposed to be a result of inter-dendrimer electronic interactions involving electronic energy donors and acceptors of different dendrimers and suggests that the title dendrimer shows features reminiscent of the energy migration patterns occurring among LH1 and LH2 assemblies of natural systems. Even in consideration of the reported use of similar dendrimers for photochemical water oxidation, the aggregation-induced energy transfer reported here, as well as the self-assembly of the light-harvesting dendrimers itself, can be useful for designing new integrated systems for solar fuel production.

(Nanocarbons Division Richard E. Smalley Research Award Address) Artificial Photosynthesis Utilizing Nanocarbons

Sustainable and clean energy resources using solar energy alternative to fossil fuels are urgently required in order to stop global warming and solve global energy and environmental issues. This award lecture focuses on our long-term developments in artificial photosynthesis for solar fuel production and its usage by utilizing nanocarbon materials. We have developed a number of photosynthetic reaction center models composed of metalloporphyrins and fullerenes with comparable charge-separated state lifetimes with that of the natural photosynthetic reaction center.[1-3] The light-harvesting unit and the charge-separation unit have been combined by utilizing coordination bonds, hydrogen bond, electrostatic interactions and p-p interactions.[4,5] The efficient photosynthetic reaction center models have been successfully combined with the catalytic water reduction unit to attain the most efficient photocatalytic hydrogen evolution system.[6-8] The activation of hydrogen has also been achieved by developing the first structural and functional model of hydrogenases,[9] which enables to replace precious Pt catalyst by much more earth-abundant metal catalyst for hydrogen evolution.[10] With regard to water oxidation, we have developed efficient and robust water oxidation catalysts using earth-abundant metal oxides nanoparticles.[11] We have also clarified the significant role of redox-inactive metal ions on enhancement of electron-transfer reactions of high-valent metal-oxo complexes, which is classified as metal ion-coupled electron transfer,[12,13] in relation with the pivotal role of Ca2+ in the oxygen evolving complex (OEC) in Photosystem II.[14,15] By combination of the catalytic four-electron water oxidation and the photocatalytic two-electron reduction of O2 using solar energy, we have succeeded in production of hydrogen peroxide (H2O2) as a solar fuel from water and O2 in the air.[16,17] We have also achieved efficient photocatalytic production of H2O2 from the most earth abundant seawater instead of precious pure water and O2 in the air using a two-compartment photoelectro-chemical cell with WO3 as a photocatalyst for water oxidation and a cobalt chlorin complex supported on a glassy-carbon substrate for the selective two-electron reduction of O2.[18] The highest solar energy conversion efficiency was determined to be 6.6% under simulated solar illumination adjusted to 0.05 sun after 1 h photocatalytic reaction (0.89% under 1sun illumination) when WO3 was replaced by the surface modified BiVO4 with iron(III) oxide(hydroxide) (FeO(OH)) as a water oxidation catalyst in the photoanode.[20] We have also developed one-compartment H2O2 fuel cells using H2O2 produced in seawater as a solar fuel and earth-abundant metal catalysts.[18,20,22] Thus, the combination of the photocatalytic H2O2 production from seawater and O2 using solar energy with one-compartment H2O2 fuel cells provides on-site production and usage of H2O2 as a more useful and promising solar fuel than H2.[18] References [1] Fukuzumi, S.; Ohkubo, K.; Suenobu, T. Acc. Chem. Res. 2014, 47, 1455-1464. [2] Fukuzumi, S. Phys. Chem. Chem. Phys. 2008, 10, 2283. [3] Fukuzumi, S.; Ohkubo, K. J. Mater. Chem. 2012, 22, 4575. [4] Fukuzumi, S.; Ohkubo, K.; D’Souza, F.; Sessler, J. L. Chem. Commun. 2012, 48, 9801-9815. [5] Yamada, M.; Ohkubo, K.; Shionoya, M.; Fukuzumi, S. J. Am. Chem. Soc. 2014, 136, 13240-13248. [6] Fukuzumi, S.; Yamada, Y.; Suenobu, T.; Ohkubo, K.; Kotani, H, Energy Environ. Sci. 2011, 4, 2754-2766. [7] Fukuzumi, S.; Yamada, Y. J. Mater. Chem. 2012, 22, 24284-24296. [8] Fukuzumi, S. Curr. Opinion Chem. Biol. 2015, 25, 18-26. [9] Ogo, S.; Kabe, R.; Uehara, K.; Kure, B.; Nishimura, T.; Menon, S. C.; Harada, R.; Fukuzumi, S.; Higuchi, Y.; Ohhara, T.; Tamada, T.; Kuroki, R. Science 2007, 316, 585-587. [10] Yamada, Y.; Miyahigashi, T.; Kotani, H.; Ohkubo, K.; Fukuzumi, S. Energy Environ. Sci. 2012, 5, 6111-6118. [11] Hong, D.; Yamada, Y.; Nagatomi, T.; Takai, Y.; Fukuzumi, S. J. Am. Chem. Soc. 2012, 134, 19572-19575. [12] Fukuzumi, S. Prog. Inorg. Chem. 2009, 56, 49-153. [13] Fukuzumi, S.; Ohkubo, K.; Lee, Y.-M.; Nam, W. Chem.–Eur. J. 2015, 21, 17548-17559. [14] Fukuzumi, S.; Morimoto, Y.; Kotani, H.; Naumov, P.; Lee, Y.-M.; Nam, W. Nat. Chem. 2010, 2, 756-759. [15] Bang, S.; Lee, Y.-M.; Hong, S.; Nishida, Y.; Seo, M. S.; Sarangi, R.; Fukuzumi, S.; Nam, W. Nat. Chem. 2014, 6, 934-940. [16] Kato, S.; Jung, J.; Suenobu, T.; Fukuzumi, S. Energy Environ. Sci. 2013, 6, 3756-3764. [17] Isaka, Y.; Kato, S.; Hong, D.; Suenobu, T.; Yamada, Y.; Fukuzumi, S. J. Mater. Chem. A 2015, 3, 12404-12412. [18] Mase, K.; Yoneda, M.; Yamada, Y.; Fukuzumi, S. Nat. Commun. 2016, 7, 11470. [19] Mase, K.; Yoneda, M.; Yamada, Y.; Fukuzumi, S. ACS Energy Lett. 2016, 1, 913-919. [20] Yamada, Y.; Yoneda, M.; Fukuzumi, S. Energy Environ. Sci. 2015, 8, 1698-1701. [21] Fukuzumi, S.; Yamada, Y. ChemElectroChem 2016, 3, in press.

Biocompatible D-A Semiconducting Polymer Nanoparticle with Light-Harvesting Unit for Highly Effective Photoacoustic Imaging Guided Photothermal Therapy.

The development of nanotheranostic agents that integrate diagnosis and therapy for effective personalized precision medicine has obtained tremendous attention in the past few decades. In this report, biocompatible electron donor-acceptor conjugated semiconducting polymer nanoparticles (PPor-PEG NPs) with light-harvesting unit is prepared and developed for highly effective photoacoustic imaging guided photothermal therapy. To the best of our knowledge, it is the first time that the concept of light-harvesting unit is exploited for enhancing the photoacoustic signal and photothermal energy conversion in polymer-based theranostic agent. Combined with additional merits including donor-acceptor pair to favor electron transfer and fluorescence quenching effect after NP formation, the photothermal conversion efficiency of the PPor-PEG NPs is determined to be 62.3%, which is the highest value among reported polymer NPs. Moreover, the as-prepared PPor-PEG NP not only exhibits a remarkable cell-killing ability but also achieves 100% tumor elimination, demonstrating its excellent photothermal therapeutic efficacy. Finally, the as-prepared water-dispersible PPor-PEG NPs show good biocompatibility and biosafety, making them a promising candidate for future clinical applications in cancer theranostics.

CuAAC-based assembly and characterization of a ruthenium-copper dyad containing a diimine-dioxime ligand framework.

The design of molecular dyads combining a light-harvesting unit with an electroactive centre is highly demanded in the field of artificial photosynthesis. The versatile Copper-catalyzed Azide-Alkyne Cycloaddition (CuAAC) procedure was employed to assemble a ruthenium tris-diimine unit to an unprecedented azide-substituted copper diimine-dioxime moiety. The resulting RuIICuII dyad 4 was characterized by electrochemistry, 1H NMR, EPR, UV-visible absorption, steady-state fluorescence and transient absorption spectroscopies. Photoinduced electron transfer from the ruthenium to the copper centre upon light-activation in the presence of a sacrificial electron donor was established thanks to EPR-monitored photolysis experiments, opening interesting perspectives for photocatalytic applications.

Synthesis and Properties of Axially Symmetrical Rigid Visible Light-Harvesting Systems Containing [60]Fullerene and Perylenebisimide.

Two visible light-harvesting perylenebisimide (PDI)-[60]fullerene (C60) systems, dyad P1 with one C60 unit and triad P2 with two C60 units, have been synthesized. Both systems are axially symmetrical with a rigid biphenyl linker, ensuring a relatively fixed spatial distance between the donor and acceptor, preventing through-space interaction, and enhancing energy transfer. Steady-state and transient spectroscopy, electrochemistry, as well as theoretical calculations have been used to investigate the electrochemical and photophysical properties of the two systems. Steady-state and time-resolved spectroscopy demonstrate that the excited state is featured by an efficient intramolecular energy transfer from PDI to C60. Then, the high efficient intrinsic intersystem crossing of C60 eventually leads to the production of the triplet C60. The extensive visible light absorption of PDI in the range of 400-650 nm and the final localization of the excited energy at the triplet C60 make these compounds ideal singlet oxygen inducers. Further investigation shows that the photooxidation capability for both compounds is significantly enhanced with respect to either PDI or C60 and even better than that of the commonly used triplet photosensitizer methylene blue (MB). The double C60 moieties in P2 display a better result, and the photooxidation efficiency of P2 increases 1.3- and 1.4-fold compared to that of P1 and MB, respectively. The combination of a light-harvesting unit with an intersystem crossing unit results in a highly efficient photooxidation system, which opens up a new way to triplet photosensitizer design.