A Cruciform Electron Donor-Acceptor Semiconductor with Solid-State Red Emission: 1D/2D Optical Waveguides and Highly Sensitive/Selective Detection of H2S Gas

In this paper, a new cruciform donor–acceptor molecule 2,2'-((5,5'-(3,7-dicyano-2,6-bis(dihexylamino)benzo[1,2-b:4,5-b']difuran-4,8-diyl)bis(thiophene-5,2-diyl))bis (methanylylidene))dimalononitrile (BDFTM) is reported. The compound exhibits both remarkable solid-state red emission and p-type semiconducting behavior. The dual functions of BDFTM are ascribed to its unique crystal structure, in which there are no intermolecular face-to-face π–π interactions, but the molecules are associated by intermolecular CN…π and H-bonding interactions. Firstly, BDFTM exhibits aggregation-induced emission; that is, in solution, it is almost non-emissive but becomes significantly fluorescent after aggregation. The emission quantum yield and average lifetime are measured to be 0.16 and 2.02 ns, respectively. Crystalline microrods and microplates of BDFTM show typical optical waveguiding behaviors with a rather low optical loss coefficient. Moreover, microplates of BDFTM can function as planar optical microcavities which can confine the emitted photons by the reflection at the crystal edges. Thin films show an air-stable p-type semiconducting property with a hole mobility up to 0.0015 cm2V−1s−1. Notably, an OFET with a thin film of BDFTM is successfully utilized for highly sensitive and selective detection of H2S gas (down to ppb levels).

Electrogenic light reactions in photosystem I: resolution of electron-transfer rates between the iron-sulfur centers.

Flash-induced voltage changes (electrogenic events) in photosystem I particles from spinach, oriented in a phospholipid layer, have been studied at room temperature on a time scale ranging from 1 micros to several seconds. A phospholipid layer containing photosystem I particles was adsorbed to a Teflon film separating two aqueous compartments. Voltage changes were measured across electrodes immersed in the compartments. In the absence of added electron donors and acceptors, a multiphasic voltage increase, associated with charge separation, was followed by a decrease, associated with charge recombination. Several kinetic phases were resolved: a rapid (<1 micros) increase, ascribed to electron transfer from the primary electron donor P700 to the iron-sulfur electron acceptor FB, was followed by a slower, biphasic increase with time constants of 30 and 200 micros. The 30-micros phase is assigned to electron transfer from FB to the iron-sulfur center FA. The voltage decrease had a time constant of 90 ms, ascribed to charge recombination from FA to P700. Upon chemical prereduction of FA and FB the 30- and 200-micros phases disappeared and the decay time constant was accelerated to 330 micros, assigned to charge recombination from the phylloquinone electron acceptor (A1) or the iron-sulfur center FX to P700.

Theoretical insights on electron donor-acceptor interactions involving carbon dioxide

Electron donor-acceptor (EDA) interactions are widely involved in chemistry and their understanding is essential to design new technological applications in a variety of fields ranging from material sciences and chemical engineering to medicine. In this work, we study EDA complexes of carbon dioxide with ketones using several ab initio and Density Functional Theory methods. Energy contributions to the interaction energy have been analyzed in detail using both variational and perturbational treatments. Dispersion energy has been shown to play a key role in explaining the high stability of a non-conventional structure, which can roughly be described by a cooperative EDA interaction.

光合放氧结构与机理的理论探索

光合放氧研究近十年来已有重要进展，但在该领域仍有很多重要问题待研究。本论文工作主要是对光系统氧化侧与光合放氧密切相关的组分的结构和性能进行理论和模拟研究，工作可概括如下： (一)、放氧中心结构和性能的探索。 1、对放氧中心Mn202单元与配体组氨酸、H2O和Cl等结合方式的理论研究显示：(a)、组氨酸和H20分子均可能与Mn202平面垂直，彼此保持较大的距离，且结合在不同的Mn离子上;(b)、2个H2O分子可能结合在不同Mn202单元上。 2、对Mn簇核心骨架的理论研究显示有必要引入新的Ca、Cl结合方式，以防止因两个Mn202单元线性化而导致2个H2O分子结合位点远离。 (二)、次级电子给体Tyr_z和Tyr_D的结构与功能。 对次级电子给体Tyr_z和Tyr_D进行精确量子化学研究显示：(a)、在中性条件下，Tyr_D和Tyr_z均只与组氨酸通过氢键作用;(b)、当失去电子后，结构发生明显变化，导致正电荷主要集中在组氨酸上，自由基主要集中在Tyr上;(c)、第三组分(H_20分子或羧基等)的引入使中性体系不容易给出电子;(d)、结合最新文献报导，推测Tyr_D~+和Tyr_z~+除与组氨酸作用外还可能分别与水和羧基作用。 (三)、原初电子给体的理论和模拟研究。 1、对紫细菌原初电子给体P_(870)的理论研究显示：(a)、双分子结构比单分子结构稳定;(b)、电荷分离之后，原初电子给体原有的空间结构不再是稳定的构型，它会向能量和化学活性均更低的构型转变。在光合细菌的原初电子给体P870中，这种转变可通过C3位的乙酰基旋转使其氧原子与另一个细菌叶绿素分子的镁原子相互作用使P870+•的总能量和化学活性明显降低。推测这种构型转变对于防止原初反应过程中的电荷重组、维持光能的高效转化有重要意义。提出了原初反应过程中结构动态变化的新观点，利用这一观点可对光合细菌原初反应动力学研究所观测到的慢过程及蛋白质微环境对原初电子给体和原初反应都有重要影响等实验现象给予较好的解释。 2、对光系统II原初电子给体P680的结构进行理论探讨，提出了两个叶绿素a分子平面间夹角为50.0±2.5°时能量最低的夹角模型。 3、采用N-甲基咪唑(C4H6N2)模拟生物体内的组氨酸，通过观测CCL4中的Chla与C4H6N2反应的吸收、CD和MCD光谱得到以下结论：(a)、在纯CCL4中，每个Chla处于5配位状态，Chla形成不对称的双聚体，彼此之间存在较强的偶合作用。提出两个Chla通过不等价的2个Mg-O配位键(O分别来自于C131位的酮基和C17位酯基的C=O)连接为紧密双体结构;(b)、当C4H6N2／Chla = 0.5和1时，其吸收、CD和MCD光谱均发生明显变化，两个Chla之间的偶合作用明显减弱，但此时仍为双聚体。推测C4H6N2首先取代原紧密双体结构中Mg-O酯键，进而取代Mg-O酮键，最后两个Chla分子通过两个Mg…O弱相互作用连接为松弛的双体结构，该模型与理论获得的P_(680)的结构相似。 在上述研究的基础上，提出了包括放氧中心外围配体和TyrZ在内的放氧中心结构新模型。在新结构模型中，2个H2O分子不对称地结合于“C”形结构开口端两个低价的Mn1II和Mn4III上，并保持较大距离;两个组氨酸的咪唑环通过N原子与两个高价的Mn2IV、Mn3IV结合;Cl结合于MB4TM，并与Ca相连;Ca通过O桥和COO-相连使两个Mn202单元保持特定空间构型。TyrZ通过组氨酸(D1-His190)与Mn簇作用。此外，新模型尝试着在O桥上引入质子。放氧中心结构及其邻近环境(包括TyrZ和TyrD)整体处于中性状态。 同时还提出了新的放氧机理，认为电子和质子的释放非同步进行，并首次明确提出两个水分子的不对称氧化和结构动态变化等观点。认为Ca在维持放氧中心的结构方面担负重要作用，C1与Mn离子之间的亲核作用变化是放氧中心结构变化的关键。

The nature of the excited state of the reaction center of photosystem II of green plants: A high-resolution fluorescence spectroscopy study

We studied the electronically excited state of the isolated reaction center of photosystem II with high-resolution fluorescence spectroscopy at 5 K and compared the obtained spectral features with those obtained earlier for the primary electron donor. The results show that there is a striking resemblance between the emitting and charge-separating states in the photosystem II reaction center, such as a very similar shape of the phonon wing with characteristic features at 19 and 80 cm−1, almost identical frequencies of a number of vibrational modes, a very similar double-Gaussian shape of the inhomogeneous distribution function, and relatively strong electron-phonon coupling for both states. We suggest that the emission at 5 K originates either from an exciton state delocalized over the inactive branch of the photosystem or from a fraction of the primary electron donor that is long-lived at 5 K. The latter possibility can be explained by a distribution of the free energy difference of the primary charge separation reaction around zero. Both possibilities are in line with the idea that the state that drives primary charge separation in the reaction center of photosystem II is a collective state, with contributions from all chlorophyll molecules in the central part of the complex.

The electron transfer complex between nitrous oxide reductase and its electron donors

J Biol Inorg Chem (2011) 16:1241–1254 DOI 10.1007/s00775-011-0812-9

Effect of the Addition of a Fused Donor-Acceptor Ligand on a Ru(II) Complex: Synthesis, Characterization, and Photoinduced Electron Transfer Reactions of Ru(TTF-dppz)(2)(Aqphen) (2+)

The synthesis and the photophysical properties of the complex [Ru(TTF-dppz)(2)(Aqphen)](2+) (TTF = tetrathiafulvalene, dppz = dipyrido-[3,2-a:2',3'-c]phenazine, Aqphen = anthraquinone fused to phenanthroline via a pyrazine bridge) are described. In this molecular triad excitation into the metal ligand charge transfer bands results in the creation of a long-lived charge separated state with TTF acting as electron donor and anthraquinone as terminal acceptor. The lifetime of the charge-separated state is 400 ns in dichloromethane at room temperature. A mechanism for the charge separation involving an intermediate charge-separated state is proposed based on transient absorption spectroscopy.

Enhancement of excess electron transfer efficiency in DNA containing a phenothiazine donor and multiple stable phenanthrenyl base pairs

EET grown ohm: Excess electron transfer (EET) was observed within a DNA duplex containing π-stacked phenothiazine as an electron donor, phenanthrenes as electron carriers and 5-bromouracil as an electron trap. Increasing the number of phenanthrenyl base pairs increased EET efficiency.

Microsomal Electron Transfer in Higher Plants: Cloning and Heterologous Expression of NADH-Cytochrome b5 Reductase from Arabidopsis

AtCBR, a cDNA encoding NADH-cytochrome (Cyt) b5 reductase, and AtB5-A and AtB5-B, two cDNAs encoding Cyt b5, were isolated from Arabidopsis. The primary structure deduced from the AtCBR cDNA was 40% identical to those of the NADH-Cyt b5 reductases of yeast and mammals. A recombinant AtCBR protein prepared using a baculovirus system exhibited typical spectral properties of NADH-Cyt b5 reductase and was used to study its electron-transfer activity. The recombinant NADH-Cyt b5 reductase was functionally active and displayed strict specificity to NADH for the reduction of a recombinant Cyt b5 (AtB5-A), whereas no Cyt b5 reduction was observed when NADPH was used as the electron donor. Conversely, a recombinant NADPH-Cyt P450 reductase of Arabidopsis was able to reduce Cyt b5 with NADPH but not with NADH. To our knowledge, this is the first evidence in higher plants that both NADH-Cyt b5 reductase and NADPH-Cyt P450 reductase can reduce Cyt b5 and have clear specificities in terms of the electron donor, NADH or NADPH, respectively. This substrate specificity of the two reductases is discussed in relation to the NADH- and NADPH-dependent activities of microsomal fatty acid desaturases.

A non-fullerene electron acceptor based on fluorene and diketopyrrolopyrrole building blocks for solution-processable organic solar cells with an impressive open-circuit voltage

A novel solution-processable non-fullerene electron acceptor 6,6′-(5,5′-(9,9-dioctyl-9H-fluorene-2,7-diyl)bis(thiophene-5,2-diyl))bis(2,5-bis(2-ethylhexyl)-3-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (DPP1) based on fluorene and diketopyrrolopyrrole conjugated moieties was designed, synthesized and fully characterized. DPP1 exhibited excellent solubility and high thermal stability which are essential for easy processing. Upon using DPP1 as an acceptor with the classical electron donor poly(3-hexylthiophene), solution processable bulk-heterojunction solar cells afforded a power conversion efficiency of 1.2% with a high open-circuit voltage (1.1 V). As per our knowledge, this value of open circuit voltage is one of the highest values reported so far for a bulk-heterojunction device using DPP1 as a non-fullerene acceptor.

Use of electronic portal imaging devices for electron treatment verification

This study aims to help broaden the use of electronic portal imaging devices (EPIDs) for pre-treatment patient positioning verification, from photon-beam radiotherapy to photon- and electron-beam radiotherapy, by proposing and testing a method for acquiring clinicallyuseful EPID images of patient anatomy using electron beams, with a view to enabling and encouraging further research in this area. EPID images used in this study were acquired using all available beams from a linac configured to deliver electron beams with nominal energies of 6, 9, 12, 16 and 20 MeV, as well as photon beams with nominal energies of 6 and 10 MV. A widely-available heterogeneous, approximately-humanoid, thorax phantom was used, to provide an indication of the contrast and noise produced when imaging different types of tissue with comparatively realistic thicknesses. The acquired images were automatically calibrated, corrected for the effects of variations in the sensitivity of individual photodiodes, using a flood field image. For electron beam imaging, flood field EPID calibration images were acquired with and without the placement of blocks of water-equivalent plastic (with thicknesses approximately equal to the practical range of electrons in the plastic) placed upstream of the EPID, to filter out the primary electron beam, leaving only the bremsstrahlung photon signal. While the electron beam images acquired using a standard (unfiltered) flood field calibration were observed to be noisy and difficult to interpret, the electron beam images acquired using the filtered flood field calibration showed tissues and bony anatomy with levels of contrast and noise that were similar to the contrast and noise levels seen in the clinically acceptable photon beam EPID images. The best electron beam imaging results (highest contrast, signal-to-noise and contrast-to-noise ratios) were achieved when the images were acquired using the higher energy electron beams (16 and 20 MeV) when the EPID was calibrated using an intermediate (12 MeV) electron beam energy. These results demonstrate the feasibility of acquiring clinically-useful EPID images of patient anatomy using electron beams and suggest important avenues for future investigation, thus enabling and encouraging further research in this area. There is manifest potential for the EPID imaging method proposed in this work to lead to the clinical use of electron beam imaging for geometric verification of electron treatments in the future.

Molecular Interactions Chlorin Assemblies and NMR Separations

Photosynthesis is a chemical process in which the energy of the light quanta is transformed into chemical energy. Chlorophyll (Chl) molecules play a key role in photosynthesis; they function in the antennae systems and in the photosynthetic reaction center where the primary charge separation (CS) takes place. Bio-inspired mimicry of the CS is an essential unit in dye-sensitized solar cells. Aim of this study was to design and develop electron donor-acceptor (EDA) pairs from Chls and fullerenes (C60) or carbon nanotubes (CNT). The supramolecular approach was chosen, as long synthetic sequences required by the covalent approach lead to long reaction schemes and low yields. Here, a π-interaction between soluble CNTs and Chl was used in EDA construction. Also, a beta-face selective two-point bound Chl-C60 EDA was introduced. In addition, the photophysical properties of the supramolecular EDA dyads were analyzed. In organic chemistry, nuclear magnetic resonance (NMR) spectroscopy is the most vital analytical technique in use. Multi-dimensional NMR experiments have enabled a structural analysis of complex natural products and proteins. However, in mixture analysis NMR is still facing difficulties. In many cases overlapping signals can t be resolved even with the help of multi-dimensional experiments. In this work, an NMR tool based on simple host-guest chemistry between analytes and macromolecules was developed. Diffusion ordered NMR spectroscopy (DOSY) measures the mobilities of compounds in an NMR sample. In a liquid state NMR sample, each of the analytes has a characteristic diffusion coefficient, which is proportional to the size of the analyte. With normal DOSY experiment, provided that the diffusion coefficients of the analytes differ enough, individual spectra of analytes can be extracted. When similar sized analytes differ chemically, an additive can be introduced into the sample. Since macromolecules in a liquid state NMR sample can be considered practically stationary, even faint supramolecular interaction can change the diffusion coefficient of the analyte sufficiently for a successful resolution in DOSY. In this thesis, polyvinylpyrrolidone and polyethyleneglycol enhanced DOSY NMR techniques, which enable mixture analysis of similar in size but chemically differing natural products, are introduced.

Study of the electronic structures of high Tc cuprate superconductors by electron energy loss and secondary electron emission spectroscopies

Energy loss spectra of superconducting YBa2Cu3O6.9' Bi1.5Pb0.5Ca2.5Sr1.5Cu3O10+δ and Tl2CaBa2Cu3O8 obtained at primary electron energies in the 170–310 eV range show features reflecting the commonalities in their electronic structures. The relative intensity of the plasmon peak shows a marked drop across the transition temperature. Secondary electron emission spectra of the cuprates also reveal some features of the electronic structure.