Photoinduced intramolecular electron transfer between fluorescein and carbazole

Several dyads consisting of a fluoreseein covalently linked with a carhazole at site 2 or site 6 have been synthesized and characterized.Studies of absorption spectra,emission spectra and fluorescence lifetime quern hing Indicate that the ground-state interaction between fluorescein and carhazole in dyads is negligible and the intramolecular electron transfer (ET) reactions are mainly of dynamic process.Moreover,the efficiency and raie conslam of lectron transfer reactions in ZFO4 (carbazole linked at site 2'of fluorescein) are larg er than those in 4FOZ (carbazole linked at site 6 of fluorescein) 0 74; KET 11×108S-1),because the mutual orientation of donor and acceptor in ZFO4 is nearly face-to-face,which is more favorable to the process than the shoulder-to-shoulder mutual orientation in 4FOZ.Estimations are also formed of the free energy change of the photomduced electron transfer and the back reactions in the dyads.     

Photoinduced intramolecular electron transfer and triplet energy transfer in a steroid-linked norbornadiene-carbazole dyad

Bichromophoric compound 3 beta-((2-(methoxycarbonyl)bicyclo[2.2.1]hepta-2,5-diene-3-yl)carboxy)androst-5-en-17 beta-yl-[2-(N-carbazolyl)acetate] (NBD-S-CZ) was synthesized and its photochemistry was examined by fluorescence quenching, flash photolysis, and chemically induced dynamic nuclear polarization (CIDNP) methods. Fluorescence quenching measurements show that intramolecular electron transfer from the singlet excited state of the carbazole to the norbornadiene group in NBD-S-CZ occurs with an efficiency (Phi SET) of about 14 % and rate constant (kSET) of about 1.6 x 10(7) s-1. Phosphorescence and flash photolysis studies reveal that intramolecular triplet energy transfer and electron transfer from the triplet carbazole to the norbornadiene group proceed with an efficiency (TET + TT) of about 52 % and rate constant (kTET + kTT) of about 3.3 x 10(5) s-1. Upon selective excitation of the carbazole chromophore, nuclear polarization is detected for protons of the norbornadiene group (emission) and its quadricyclane isomer (enhanced absorption); this suggests that the isomerization of the norbornadiene group to the quadricyclane proceeds by a radical-ion pair recombination mechanism in addition to intramolecular triplet sensitization. The long-distance intramolecular triplet energy transfer and electron transfers starting both from the singlet and triplet excited states are proposed to proceed by a through-bond mechanism.     

Intermolecular and intramolecular electron transfer from eosin ester to viologen

The covalently -(CH2)10- linked eosin-butylviologen compound has been synthesized. The photoinduced electron transfer of eosin ester and butylviologen as well as the influence of addition of cyclodextrin or amylose into the solution of linked compound on the system have been studied by the absorption spectra, fluorescence spectra and fluorescence lifetime. The results indicated that the intramolecular electron transfer is much more efficient than the intermolecular one. Due to the formation of inclusion complex, the process of intramolecular electron transfer was changed after adding cydodextrin or amylose.     

Photoinduced electron transfer dynamics in porphyrin donor dyads

Intramolecular photoinduced electron transfer (PET) processes occurring in dyads with a free base porphyrin-tetraazaanthracene donor (P) and either a tetracyanonaphthoquinidodimethane (TCQ) or benzoquinone (BQ) acceptor linked by a rigid six σ-bond polynorbornane bridge ([6]) have been investigated. For P[6]BQ, PET in the polar solvent benzonitrile (_s = 25.9) occurs with a rate constant (k_PET) of 1.6 × 10⁸ s⁻¹ but is not evident in solvents less polar than tetrahydrofuran (_s = 7.52). For P[6]TCQ, highly efficient forward PET occurs in both polar and non-polar solvents (k_PET > 2 × 10¹⁰ s⁻¹). For P[6]TCQ the lifetime of the resulting charge-separated state decreases markedly with increasing solvent polarity. The results are discussed in the context of the likely mechanisms for electronic coupling and current theories for PET processes in such linked molecular systems.     

Photoinduced intramolecular electron transfer of fluorescein and violgen, carbazole

A series of polyads consisting of covalently-(CH2)4-linked fluorescein with carbazole and violger.Live been synthesized and characterized The studies of absorption,emission spectra and fluorescence lifetime quenching indicated that the intramolecular fluorescence quenching of fluorescein by violgen is mainly a static process through the formation of non emission complex (fluorescence quenching efficiency φQ=0.97,lifetime quenching efficiency φH 0,quenching efficiency of formation of non-emission complex φC=0.97); while the quenching by carbazole is mainly a dynamic electron transfer process (φQ=0.63,φET=0.63,φC=0).In the violgen-fluorescein-carbazole triads,φQ=0.97,Q ET=0.65,φC=0.32,which suggests that the photoinduced interaction of fluorescein-carbazole pair and that of violgen-fluorescein pair are in a competitive process,the dynamic electron transfer from carbazole to fluorecein is dominant in the process The free energy change of the photoinduced electron transfer and the back reac-tiorns i     

Photoinduced intramolecular electron transfer and charge separation in zinc phthalocyanine-viologen linked system

Photoinduced electron transfer and charge separation processes in zinc phthalocya-nine-viologen linked system have been studied and the distance effect of donor/acceptor on electron transfer reaction is discussed. It is indicated that the fluorescence from the zinc phthalocyanine moiety is appreciably quenched and the life-time of singlet excited state is reduced by the pendant viologen. Time-resolved transient absorption spectra measurements show that intramolecular quenching of the triplet state of zinc phthalocyanine by the attached viologen results in charge separation giving reduced viologen radical alive for a rather long period with hundred microsecond duration. The effect of the carbon chain length on the electron transfer rate constant and charge separation efficiency suggests that upon excitation, the zinc phthalocyanine and viologen groups tend to take closer conformation with the increase of the carbon chain examined. The rate constant for the intramolecular electron transfer ket with n = 3     

光捕获树枝形聚合物体系能量传递和电子转移研究进展

树枝形聚合物是一类围绕着中心核,外围链段和官能团呈指数增长的支化高分子.合成方法的发展使发色团可被精确地置于树枝形聚合物的核心、外围甚至支化节点处.树枝形聚合物的特殊结构使其作为模拟光捕获体系被广泛研究.光诱导电子转移和能量传递是光合作用中的重要过程,研究树枝形聚合物体系中的电子转移和能量传递对未来树枝形聚合物在光电器件中的应用有着重要意义.本文综述了近年来光捕获树枝形聚合物体系的研究进展,并重点介绍光捕获树枝形聚合物体系中的能量传递和电子转移过程研究.     

Photoinduced electron transfer in alpha-cyclodextrin-based supramolecular dyads: a free-energy-dependence study

Photoinduced electron transfer (PET) between alpha-cyclodextrin-appended pyrene (PYCD) and a few acceptor molecules was studied in aqueous solutions. The pyrene moiety in PYCD is located above the narrower rim of the alpha-CD and is fully exposed to water. The acceptors are monocyclic organic molecules and, upon dissolution in water in the presence of PYCD, a fraction of the donor-acceptor systems is present as supramolecular dyads and the remaining fraction as free molecules. Free-energy-dependence studies showed that electron transfer in the supramolecular dyads follows the Marcus equation. The donor-acceptor coupling and the reorganization energy were determined from fits of the data to the Marcus equation. The electronic coupling was found to be similar to those reported for hydrogen-bonded systems. It appears that the actual lambdaout values are somewhat lower than values calculated with the continuum model. The experimental design has also allowed, for the first time, a visual demonstration of the inverted region on the basis of the raw fluorescence lifetime data.     

Contrasting photodynamics between C60-dithiapyrene and C60-pyrene dyads

The photodynamics of a C60-dithiapyrene donor-acceptor conjugate were compared with the corresponding C60-pyrene conjugate. The photoinduced charge separation and subsequent charge recombination processes were examined by time-resolved fluorescence measurements on the picosecond timescale and transient absorption measurements on the picosecond and microsecond timescales with detection in the visible and near-infrared regions. We have observed quite long lifetimes (i.e., up to 1.01 ns) for the photogenerated charge-separated state in a C60-dithiapyrene dyad without the need for i) a long spacer between the two moieties, or ii) a gain in aromaticity in the radical ion pair.     

卟啉-噁二唑二元体系光诱导能量及电子传递研究

以5-对氨基苯基-10,15,20-三苯基卟啉及2-苯基-5-(对氨基苯基)-1,3,4-噁二唑为原料合成了系列卟啉-噁二唑二元化合物, 其结构通过¹H NMR, ESI-MS, IR, UV-Vis确定. 对合成化合物进行光谱性能测定, 结果表明, 在卟啉与噁二唑混合体系中, 存在着卟啉激发态分子向噁二唑基态分子的分子间电子传递过程, 导致卟啉激发态的荧光猝灭; 在卟啉-噁二唑二元体系中, 315 nm激发下发生了由激发态噁二唑基团至卟啉基团的能量传递, 导致噁二唑基团荧光猝灭, 卟啉基团荧光增强. 420 nm激发下不存在分子内卟啉基团向噁二唑基团的电子回传竞争; 电化学性能测定进一步表明从噁二唑基团向卟啉基团的电子传递是可能的. 因此卟啉-噁二唑二元化合物可能作为一种模型, 模拟光合作用中电子给体至叶绿素之间的电子传递过程.     

Photoinduced Energy- and Electron-Transfer Processes in a Side-to-Face RuII-Porphyrin/Perylene-bisimide Array

A side-to-face array DPy-gPBI[Ru(4-tBuTPP)(CO)]₂, based on a “green” perylene bisimide chromophore sandwiched between two Ru^II-porphyrins, has been prepared by self-assembly. Its photophysical properties have been characterized in detail by a combination of steady-state and time-resolved techniques upon selective excitation of the two different components. Different photoinduced processes are observed as a function of the excitation wavelength. Electron transfer quenching is attained upon “red light” excitation of the perylene unit, whilst an energy transfer pathway is followed upon “green light” excitation of the metallo-porphyrin moiety. Regardless of the excitation wavelength efficient population of the triplet excited state of the perylene chromophore is achieved. The photophysical results are discussed within the framework of classical electron transfer theory and compared with those of a previously reported system.     

Intermolecular interaction between squarylium cyanine and porphyrin

In this paper, the interaction between squarylium cyanine and porphyrin in chloroform is investigated by absorption and fluorescence spectroscopy. Emphasis has been put on the mechanism of intermolecular energy transfer. The overlap integral J between the absorption spectrum of squarylium cyanine and the fluorescence spectrum of porphyrin was calculated, which reveals that the singlet-singlet energy transfer may occur from porphyrin to squarylium cyanine in solution. In comparison of the observed rate constant [kqII=6.1 ×1013 (mol/L)-1·s-1] for fluorescence quenching of porphyrin by squarylium cyanine with the diffusion rate constant in chloroform [kdif=1.1×1010 (mol/L)-1·s-1] and the rate of energy transfer [ket≤6.7×104 (mol/L)-1·s-1 in the experimentally dilute solutions] estimated from Forster formula, the possibility of energy transfer by electron exchange or/and coulombic mechanism could be excluded. So it has been definitely convinced that the intermolecuiar energy transfer between them is     

Photoinduced Electron and Energy Transfer in Dyads of Porphyrin Dimer and Perylene Tetracarboxylic Diimide

Two compounds containing a porphyrin dimer and a perylene tetracarboxylic diimide (PDI) linked by phenyl ( 1 ) or ethylene groups ( 2 ) are prepared. The photophysical properties of these two compounds are investigated by steady state electronic absorption and fluorescence spectra and lifetime measurements. The ground state absorption spectra reveal intense interactions between the porphyrin units within the porphyrin dimer, but no interactions between the porphyirn dimer and PDI. The fluorescence spectra suggest efficient energy transfer from PDI to porphyrin accompanied by less efficient electron transfer from porphyrin to PDI. The energy transfer is not affected by the dimeric structure of porphyrin or the linkage between the porphyrin dimer and PDI. However, the electron transfer from porphyrin to PDI is significantly affected by either the linkage between the donor and the acceptor or the polarity of the solvents. The dimeric structure of the porphyrin units in these compounds significantly promotes electron transfer in nonpolar, but not in polar solvents.     

Photoinduced Electron Transfer Reaction between N,N-Dimethylaniline and 7,7-Dichloronorcarane

OxidativedealkylationoftertiarytaineshasattractedconsiderableattentionduetoitsrelevancetoenzymahcN-dealkylationandasamodelreactionofcytochromeP-450oxidation_1.IthasbeenreportedthattheoxidativedemethylationofN,N-dimethylaniline(DMA)couldbeaccomplishedchendcally_2,electrochemically_3andphotochemically_4.Ingeneral,anelectronacceptivesensitizerorinitiatormustbeusedtoinitiatethephotochemicalreaction,andthereactionproductsandmechanismsdependonthesensitizerorinitiatorused.Forinstance,whendicyanona…     

四氯化苯醌-二苯撑体系的光诱导电子转移研究

用从头算方法对四氯化苯醌-二苯撑体系分子间相互作用进行了理论计算研究.用MP2/6-31G^**方法,分别优化电子给体二苯撑,受体四氯化苯醌的稳定构型,用同样的方法优化配合物的层间距得到其最稳定构型,并计算了BSSE校正后的电子给受体配合物的稳定化能.用CIS/6-31++G^**方法,计算了给体、受体及配合物的电子激发态.理论计算验证了给体和受体间能形成稳定的电子给受体配合物,该配合物受光激发能直接产生电荷转移态.在球孔穴近似和点偶极近似下,对电荷转移吸收的理论计算结果进行了非平衡溶剂化能校正.经非平衡溶剂化能校正的电荷转移跃迁能与实验值符合较好.     

Dendronized perylenetetracarboxdiimides with peripheral triphenylamines for intramolecular energy and electron transfer

Novel perylene-3,4,9,10-tetracarboxdiimides (PDI) dyes functionalized with polyphenylene dendrimers attached at the bay region are reported. Derivatives of PDI bearing polyphenylene dendrimers up to the second generation, substituted with an increasing number of triphenylamine (TPA) moieties at the periphery, as well as a related nondendronized model compound were prepared. Intramolecular energy transfer was demonstrated by the observation of PDI emission on excitation of the triphenylamines, and electron transfer was detected by comparing photoluminescence quenching in solvents of different polarity.     

痂囊腔菌素A与咔唑化合物间的光致电子转移

研究了咔唑、咔唑-9-乙酸、3-溴-咔唑-9-乙酸在缺氧条件下对天然苝醌化合物痂囊腔菌素A(简记为EA)的荧光猝灭行为;由竹红菌甲素(HA)和乙素(HB)的荧光寿命估算了EA在乙腈中的荧光寿命,并进而计算了三个咔唑化合物的双分子猝灭速度常数.结果表明,三个咔唑化合物在EA的可见光吸收区无光吸收,据此推测其对EA的荧光猝灭作用归因于咔唑化合物作为电子给体而EA作为电子受体的光致电子转移作用.三个咔唑化合物的Stern-Volmer猝灭常数分别为698、704和1 063L·mol-1;乙酸基对咔唑环的光致电子转移速率几乎没有影响,而溴原子取代能够增加咔唑化合物对EA的荧光猝灭程度和光致电子转移速率.此外,EA在乙腈中的荧光寿命为1.98ns,而三个咔唑化合物的双分子猝灭速率常数分别为3.52×1011,3.56×1011和5.37×1011 L·mol-1·s-1.     

Photoinduced electron transfer between the interlocked components of porphyrin catenanes: effect of the presence of nonequivalent reduction sites on the charge recombination rate

[2]Catenanes made up of several polyether-strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat-p-phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro-active subunits. The redox patterns represent useful "fingerprints" that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with tau=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge-separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41+/-4 ps. Comparison of the electron transfer rates CS and CR in the host-guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two-step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination.