Photochemical charge separation in closely positioned donor-boron dipyrrin-fullerene triads

A series of molecular triads, composed of closely positioned boron dipyrrin-fullerene units, covalently linked to either an electron donor (donor(1)-acceptor(1)-acceptor(2)-type triads) or an energy donor (antenna-donor(1)-acceptor(1)-type triads) was synthesized and photoinduced energy/electron transfer leading to stabilization of the charge-separated state was demonstrated by using femtosecond and nanosecond transient spectroscopic techniques. The structures of the newly synthesized triads were visualized by DFT calculations, whereas the energies of the excited states were determined from spectral and electrochemical studies. In the case of the antenna-donor(1)-acceptor(1)-type triads, excitation of the antenna moiety results in efficient energy transfer to the boron dipyrrin entity. The singlet-excited boron dipyrrin thus generated, undergoes subsequent energy and electron transfer to fullerene to produce a boron dipyrrin radical cation and a fullerene radical anion as charge-separated species. Stabilization of the charge-separated state in these molecular triads was observed to some extent.     

Photoinduced energy transfer and charge transfer on squarylium cyanine dyes

A series of squarylium cyanine dyes (Sqs) were synthesized to explore their applications in functional devices.Preliminary investigation on the mechanism involved in these devices was carried out.Spectroscopic behavior of Sqs with porphyrin (P),8-hydroxyquinolium aluminum (Alq) and ruthenium bipyridyl complex (Ru(bipy)) in solution,in film and on nanocrystalline TiO2 was investigated,respectively.A mechanism including photoinduced energy transfer and charge transfer processes was suggested in the corresponding practical devices.By means of doping,a red organic electroluminescent device (ELD) using Sq-doped Alq as the emission layer (EML) has been developed,and the total light to electricity efficiency of nanocrystalline TiO2 electrode based on using Sq-doped Ru(bipy) as photosensitizer has been improved greatly in the whole visible region,particularly in the red area above 600 nm.     

荷移分光光度法测定头孢拉定

采用紫外可见分光光度法研究了头孢拉定与茜素之间的荷移反应,从而建立了一种快速简便测定头孢拉定的荷移分光光度法。实验表明,在乙醇-水介质中,头孢拉定与茜素在30℃水浴中反应45 min后形成稳定的1∶1型荷移络合物,该络合物的λmax=524 nm,表观摩尔吸光系数为2.01×10^4L.mol^-1.cm^-1。头孢拉定药物质量浓度在0.87-87μg/mL范围内服从比尔定律,r=0.9990。相对标准偏差为1.1%（n=7）,加标回收率为91.4%-103.6%。     

Distal charge transport in peptides

Biological systems often transport charges and reactive processes over substantial distances. Traditional models of chemical kinetics generally do not describe such extreme distal processes. In this Review, an atomistic model for a distal transport of information, which was specifically developed for peptides, is considered. Chemical reactivity is taken as the result of distal effects based on two-step bifunctional kinetics involving unique, very rapid motional properties of peptides in the subpicosecond regime. The bifunctional model suggests highly efficient transport of charge and reactivity in an isolated peptide over a substantial distance; conversely, a very low efficiency in a water environment was found. The model suggests ultrafast transport of charge and reactivity over substantial molecular distances in a peptide environment. Many such domains can be active in a protein.     

Acid/base sensitive platinum terpyridyl complex: Switching between metal-to-ligand charge transfer (MLCT), ligand-to-ligand charge transfer (LLCT), and intraligand charge transfer (ILCT) states

A platinum(II) 2,2′:6′,2″-terpyridyl complex (2) with a hydroxylphenyl substituent on the terpyridyl ligand and a dimethylamino substituent on the phenylacetylide ligand was synthesized and characterized. Complex 2 exhibits a metal-to-ligand charge transfer (¹MLCT) absorption band at ca. 410 nm and a ligand-to-ligand charge transfer (¹LLCT) band at ca. 536 nm. It exhibits dual emission at ca. 450 nm and ca. 560 nm at room temperature when excited at 334 nm, which originates from the ¹π,π* state and the ³MLCT/³π,π* state, respectively. Dramatic color change was observed for 2 with addition of acid and base. Its emission at 560 nm was enhanced in acidic solution and quenched in basic solution. The changes in absorption and emission could be attributed to the variation of the nature of the lowest excited state from LLCT to MLCT in acidic solution and to LLCT/ILCT at basic solution. The drastic color and emission intensity changes in acidic and basic solutions suggest that 2 could potentially be a colorimetric and luminescent acid/base sensor.     

Is it common for charge recombination to be faster than charge separation?

Attaining long-lived charge-transfer (CT) states is of the utmost importance for energy science, photocatalysis, and materials engineering. When charge separation (CS) is slower than consequent charge recombination (CR), formation of a CT state is not apparent, yet the CT process provides parallel pathways for deactivation of electronically excited systems. The nuclear, or Franck-Condon (FC), contributions to the CT kinetics, as implemented by various formalisms based on the Marcus transition-state theory, provide an excellent platform for designing systems that produce long-lived CT states. Such approaches, however, tend to underestimate the complexity of alternative parameters that govern CT kinetics. Here we show a comparative analysis of two systems that have quite similar FC CT characteristics but manifest distinctly different CT kinetics. A decrease in the donor-acceptor electronic coupling during the charge-separation step provides an alternative route for slowing down undesired charge recombination. These examples suggest that, while infrequently reported and discussed, cases where CR is faster than CS are not necessarily rare occurrences.     

Dioxastilbenophanes—synthesis and charge transfer complexation studies

Intramolecular McMurry coupling of dialdehydes derived from xylenyl dibromide and 4-hydroxy benzaldehyde afforded cis-stilbenophanes along with cyclophane diols. Stilbenophanes with a large cavity were also synthesized. Charge transfer complexations of the stilbenophanes with TCNE, TCNQ and PQT were studied. Some stilbenophanes form a relatively stronger complex with PQT rather than with TCNE and TCNQ.     

Mechanism of charge separation in DNA by hole transfer through consecutive adenines

To investigate the mechanism of charge separation in DNA with consecutive adenines adjacent to a photosensitizer (Sens), a series of naphthalimide (NI) and 5-bromouracil ((br)U)-modified DNAs were prepared, and the quantum yields of formation of the charge-separated states (Phi) upon photo-excitation of the Sens NI in DNA were measured. The Phi was modulated by the incorporation site of (br)U, which changes the oxidation potential of its complementary A through hydrogen bonding and the hole-transfer rates between adenines. The results were interpreted as charge separation by means of the initial charge transfer between NI in the singlet excited state and the second- and third-nearest adenine to the NI. In addition, the oxidation of the A nearest to NI leads to the rapid charge recombination within a contact ion pair. This suggests that the charge-separation process can be refined to maximize the Phi by putting a redox-inactive spacer base pair between a photosensitizer and an A-T stretch.     

First experimental evaluation of partial charge transfer during anion adsorption

The partial charge transfer during anion adsorption cannot be measured in electrochemical experiments or reliably estimated by ab initio quantum-chemical and DFT calculations. However, it is directly involved in the adsorbate charge that is experimentally accessible by in situ contact electric resistance technique. We present the first quantitative evaluation of charge transfer during halides adsorption on silver from aqueous solutions in dependence on the electrode potential. Partial charge transfer from adsorbed bromide and iodide ions to the silver electrode increases with the positive potential shift and may reach complete charge transfer resulting in adatom creation. Chloride adsorption on silver occurs with much lower charge transfer, but on some stainless superalloys it proceeds with substantial charge transfer owing to their specific electronic structure.     

Impact of bridging units on the dynamics of photoinduced charge generation and charge recombination in donor-acceptor dyads.

We estimate, at a full quantum-chemical level, the various molecular parameters governing the rate of photoinduced charge generation and charge recombination in model organic structures containing a donor and an acceptor unit in view of the possible use of such systems in organic solar cells. The rate of through-space excitation dissociation, as predicted in the framework of the Marcus-Levich-Jortner theory, is found to be low in comparison to intramolecular decay processes when the donor and acceptor molecules are lying in a head-to-tail arrangement and high when the donor and acceptor molecules are superimposed in a cofacial arrangement. The charge separation rates for side-by-side donor-acceptor dyads are significantly increased by promoting through-bond interactions in covalently linked donor and acceptor units. This has motivated a detailed quantitative analysis of the influence of the nature, size, and conformation of the bridging moiety on the calculated transfer rates.     

电化学方法用于分子内电荷转移特性的研究

设计合成一系列具有不同取代基的苯甲酰萘（苯）胺衍生和，测定它们在非极性溶剂环己烷中的荧光发射光谱，发现系列合成产物具有双重荧光，其长滤发射具有电荷转移特性，其长波发射态能量与不同取代基的苯甲酰萘（苯）胺衍生物的失（得）电子能力，即给（受）体的氧化还原电位之间符合Weller方程。     

Metal atom dynamics in a charge transfer complex

Temperature-dependent ⁵⁷Fe Mössbauer spectroscopy over the interval 89 < T < 335 K has been used to study the detailed metal atom dynamics in the charge transfer complex (CT) decamethlferrocene-acenaphthenequinone. The quadrupole splitting, area ratio and recoil-free fraction parameters clearly reflect the phase transition (T_pt) at 257 K. The root-mean-square-amplitude of vibrations of the metal atom in the CT complex have been compared to that determined earlier for decamethyl ferrocene. The vibrational amplitudes are isotropic below T_pt but anisotropic above this temperature.     

Theoretical investigation of charge transfer excitation and charge recombination in acenaphthylene–tetracyanoethylene complex

Ab initio calculations were performed to investigate the charge separation and charge recombination processes in the photoinduced electron transfer reaction between tetracyanoethylene and acenaphthylene. The excited states of the charge‐balanced electron donor–acceptor complex and the singlet state of ion pair complex were studied by employing configuration interaction singles method. The equilibrium geometry of electron donor–acceptor complex was obtained by the second‐order Møller–Plesset method, with the interaction energy corrected by the counterpoise method. The theoretical study of ground state and excited states of electron donor–acceptor complex in this work reveals that the S₁ and S₂ states of the electron donor–acceptor complexes are excited charge transfer states, and charge transfer absorptions that corresponds to the S₀ → S₁ and S₀ → S₂ transitions arise from π–π* excitations. The charge recombination in the ion pair complex will produce the charge‐balanced ground state or excited triplet state. According to the generalized Mulliken–Hush model, the electron coupling matrix elements of the charge separation process and the charge recombination process were obtained. Based on the continuum model, charge transfer absorption and charge transfer emission in the polar solvent of 1,2‐dichloroethane were investigated. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 23–35, 2003     

Solvent effect on the charge transfer complex of oxatomide with 2,3-dichloro-5,6-dicyanobenzoquinone

The charge transfer complex (CT-complex) between oxatomide drug and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was studied spectrophotometrically in 10 solvents at different temperatures. The donor oxatomide is found to form stable 1:1 stoichiometric complex with DDQ and the stoichiometry was unaffected by change in polarity of the solvent studied. The DeltaH degrees, DeltaS degrees and DeltaG degrees values are all negative, so the studied complex is reasonably stable and exothermic in nature. The ionization potential of the drug was determined using the CT-absorption bands of the complex in all the solvents. The dissociation energy of the charge transfer excited state for the CT-complex in different solvents was also determined and is found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the nature of the solvent.     

奈韦拉平与铬天青S的电荷转移反应及其测定

确定了奈韦拉平与铬天青S的电荷转移反应条件,同时建立了测定奈韦拉平的分光光度法。奈韦拉平与铬天青S在水和丙酮混合溶剂中发生电荷转移反应,常温下反应30min后可比色。电荷转移络合物的最大吸收波长是578nm,表观摩尔吸光系数为1.78×104L·mol-1·cm-1。奈韦拉平质量浓度在1～16μg·mL-1范围内服从比耳定律,相关系数为0.9993。当奈韦拉平浓度为6μg·mL-1时,六次测定结果的相对标准偏差为1.61%。测得荷移络合物的组成和稳定常数分别为1∶1和1.73×104。本方法用于测定制剂中奈韦拉平的含量,结果与文献方法一致,回收率在98.0%以上。