Combined Transient Spectra and Semiempirical Calculation of [60]Fullerenes Attached with Piperidinodithiocarboxylate and 7-Chloro-phenazine

[60]Fullerenes attached with piperidinodithiocarboxylate dyad （1） and 7-chloro-1,2,3,4-tetrahydrophenazine （2） were efficiently synthesized through Diels-Atder cycloaddition with dienes. The physical properties of the triplet states of these compounds, in which strong electron acceptor moieties were covalently attached to C60 cores, were investigated by nanosecond laser flash photolysis. The excited triplet states in benzonitrite have been evaluated by observing the transient absorption bands in the near-IR region. The HOMO and LUMO were calculated by semiempirical methods AM1, which could predict the intramolecular photoinduced electron transfer in 1 and 2, and the nanosecond transient absorption spectra observed experimentally in solution were in excellent agreement with the calculated ones.     

Quantum chemical study on excited states and charge transfer of oxazolo[4,5-b]-pyridine derivatives

The excitedstate intramolecular charge transfer of four oxazolo[4,5-b]pyridine derivatives with different electron donating and electron withdrawing groups was investigated using the time-dependent density functional theory. The vertical excitation energies and the electronic structures were explored. Their distinct properties of absorption and fluorescence spectra in solvent phase were explained according to the electronic coupling matrix elements calculated by the Mulliken-Hush theory. The sub-stituent on the oxazolo[4,5-b]pyridines will remarkably change their spectra properties and increase the first excited-state dipole moments. The effect of protonation on the absorption and fluorescence spectra was also investigated systematically. Our study suggests that the present method is feasible to explain charge transfer excitation and predict the properties of absorption and emission spectra in the studied systems.     

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     

Solvent effects on competitive intramolecular electron transfer and energy transfer in a covalently linked porphyrin-phthalocyanine heterodimer

Photophysical properties of a porphyrin-phthalocyanine heterodimer covalently linked with a dipentoxy chain have been studied.Absorption spectra show that there is weak exciton coupling between the two chromophores in the ground state.Fluorescence spectra show that intramolecular energy transfer from porphyrin to phthalocyanine moiety occurs in competition with electron transfer.The efficiency of these two processes depends upon the mutual orientation of the two chromophores.The effect of solvent polarity on the intramolecular processes is also discussed.     

Fluorescence Quenching Study of Zinc Bisporphyrins by Fulleropyrrolidines and Their N-Oxides

Novel phenylene-bridged zinc bisporphyrins （1-4）, fulleropyrrolidines （C60-m, C60-h） and their N-oxides （C60-mo, C60-ho） were synthesized. The fluorescence quenching processes of bisporphyrins in toluene solution by fulleropyrrolidines and their N-oxides were investigated by steady-state fluorescence spectra. The fluorescence quenching constants proved that the fluorescence quenching ability was decreased as reduction of the pyrrolidine functional groups of fullerene surface： C60-h〉C60-m〉C60, and the fluorescence quenching ability was increased about 1.3-7.4 times by utilizing fulleropyrrolidine N-oxides （C60-mo, C60-ho） compared to fulleropyrrolidine compounds （C60-m, C60-h）. The results revealed photoinduced electron transfer （PET） efficiency between bispor-phyrin and fullerene derivatives could be tunable by change of functional groups on fullerene surface.     

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.     

Charge Transfer Properties of Organic Semiconductor Molecules of Perylene Derivatives

The charge transfer rates of perylene and its four derivatives were studied at the level of B3LYP/6-31G** by density functional theory. The results showed that the perylene and its four derivatives belonged to the semiconductor molecules, which released energy when electron was injected. Therefore, they were suitable to be used as the electron injection material. The introduction of OH group can improve the electron transfer rate significantly. The formations of intramolecular hydrogen bonds were unfavorable to the hole transfer, but conducive to the electron transfer. The perylene derivatives, 2,5-3,4,5-(trifluorophenyl)ethynyl-8,11-3,4,5-trihydroxyphenyl ethynyl, designed in this article had the hole transfer rate of 1.57 cm2/V·s-1. Therefore, this kind of material will be potential hole transfer material with high transfer efficiency.     

Research on the Synthesis and Optical Properties of Isomeric Bichromophoric Compounds --3-or 4- Phenyl 7-Coumarin ω-9-Anthracene-Poly-methene Carboxylate

Six bichromophoric compounds-substituted coumarin ω -9-anthra-cene-poly-methene carboxylate and five model compounds were synthesized. Among them, eight compounds are new ones. Intramolecular singlet energy transfer has been demonstrated in the bichromophoric compounds 1? and studied in some detail. The absorption spectra of the compounds 1-6 bear evidence that the π-electron systems of coumarin and anthracene ring do not overlap appreciably. The coumarin moiety of the bichromophoric compounds molecule was excited at 314nm and the resulting fluorescence was characteristic of the anthracene group. The efficiency of transfer of singlet excitation from coumarin moiety to the anthracene grou is about 100% in both calculation and observation and the rate of the singlet energy transfer is about 1014 sec in the compounds 4-6. A possible mechanism of intramolecular energy transfer was suggested. The difference between 4-phenyl compounds 1-3 and 3-phenyl compounds 4-6 in spectra was com -pared.     

Photoinduced intermolecular and intramolecular actions between eosin and porphyrin

Two dyads of eosin and porphyrin linked with a semi-rigid (-CH2phCH2-) or flexible (-(CH2)4-) bridge and their reference model compounds were synthesized and characterized The intermoleccular interaction and intramolecular photoinduced singlet energy transfer and electron transfer were studied by their absorp tion spectra,fluorescence emission,excitation spectra and fluorescence lifetime The model compounds,ethyl ester of eosm (EoEt) and porphyrin (PorEt),could form complexes in the ground state.When the eosin moieties in dyads were excited,they could transfer some singlet energy to the porphyrins; in the meantime,they could also ndsce electron transfer between two chromophores.Exciting the porphyrin moieties in dyads could induce electron transfer from eosin moieties to porphyrin moieties.The efficiencies (EnT,ET) and rate constants (kEnT,kET) were related to the polarity of solvents and mutual orientation of the two chromophores in dyads.     

A One-pot Procedure to Prepare Ethynylferrocene and Iodoethynylferrocene

IntroductionFerrocene-containing compounds have been widely used as important probes to investigate the electron transfer/transport properties of the molecular materials1. Recently, this technique was employed in molectronics research, where the ferrocenes were incorporated on the ends of conjugated molecular wires, and the electron transfer/transport abilities of the molecular wires were conveniently studied by electrochemical method2. Ethynylferrocene and iodoethynylferrocene were two import…     

Synthesis, charge-separated state characterization of N-methyl-2-(4′-N-ethylcarbozole)-3-fulleropyrrolidine and its derivatives

N-Methyl-2-(N-ethylcarbozole)-fulleropyrro lidine and N-methyl-2-(4′-N,N-diphenylaminophenyl)-fulleropyrrolidine were synthesized by 1,3-dipolar cycloaddition under microwave irradiation, which were characterized by MS, ¹H NMR, IR and UV-Vis. Photoinduced intramolecular electron transfer process from C₆₀ moiety to carbazole moiety has been studied by nanosecond laser flash photolysis. The charge-separated state C₆₀ ^•−-Cz^•+ was observed in the near-IR region with a lifetime of 0.28 μs. The electronic spectrum of the C₆₀-TPA was studied by using ZINDO method on the basis of the optimized geometrics with B3LYP/6-31G* program. The results show that the calculated absorption was beyond 440nm, essentially consistent with the experimental value 433 nm. __________ Translated from Acta Chimica Sinica, 2005,63(17)(in Chinese)     

N-甲基-2-(4'-N-乙基咔唑基)-[60]富勒烯吡咯烷及其衍生物的合成, 电荷分离态特征

通过1,3-偶极环加成方法在微波照射下合成了N-甲基-2-(4'-N-乙基咔唑基)-富勒烯吡咯烷(C₆₀-Cz)和N-甲基-2- (4'-N,N-二苯基氨基)-富勒烯吡咯烷(C₆₀-TPA), 用质谱, ¹H NMR, IR等对其结构进行了表征. 用激光光解时间分辨瞬态谱研究了N-甲基-2-(4'-N-乙基咔唑基)-富勒烯吡咯烷的分子内电荷转移过程, 在近红外区观测到了长寿命电荷分离态C₆₀^•--C_Z^•+的存在, 其寿命为0.28 μs. 运用Gaussian 98量子化学程序包, 利用密度泛函的方法对N-甲基-2-(4'-N,N-二苯基氨基)-富勒烯吡咯烷几何构型进行了优化, 并在优化基础上用ZINDO方法计算了化合物C₆₀-TPA的电子光谱, 计算结果表明, 光谱吸收峰在440 nm, 与实验值433 nm基本一致.     

Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C60 and Triphenylamine–Corrole‐C60 Donor–Acceptor Conjugates

Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C₆₀ , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C₆₀) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C₆₀ . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from ¹ TPA* to the corrole and subsequent electron transfer from ¹corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor^?+ in Cor‐C₆₀ and TPA‐Cor^?+ in TPACor‐C₆₀ ) and fullerene radical anion (C₆₀^??), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k_CS, was found to be about 10¹¹ s^?1, suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k_CS, the rate of charge recombination, k_CR, was also found to be rapid (k_CR≈10¹⁰ s^?1), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of ³corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of ³corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.     

Spectra of optical phonons and low-energy electronic transitions in C60/TMPD and C60/TPA single crystals

Single Crystals of C₆₀/TMPD and C₆₀/TPA have been grown from a chlorobenzene solution. Optical transmission spectra of single crystals of fullerene complexes withN,N,N,N-tetramethyl-p-phenylenediamine (TMPD) and triphenylamine (TPA) are studied in the spectral range from 600 to 16000 cm^–1. Splitting of the intramolecular vibration of C₆₀ is observed at 1428 cm^–1, which is likely caused by freezing of the rotation of the C₆₀ molecules due to their interaction with amines. Single crystals of C₆₀/TMPD differ from those of C₆₀/TPA by a decrease in the vibration frequency at 1428 cm^–1, vibrations of the C-C bonds of the TMPD molecule, and the redistribution of the forces of the oscillators of the vibrations of the C-N bonds. These peculiarities are interpreted to be the result of partial electron transfer from TMPD to C₆₀ in the C₆₀/TMPD single crystals. The electron transfer in the C₆₀/TPA system is less pronounced.Translated fromIzvestiya akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1459–1464, June, 1996     

Photoinduced Energy and Electron Transfer in Phenylethynyl‐Bridged Zinc Porphyrin–Oligothienylenevinylene–C60 Ensembles

Donor–bridge–acceptor triad (Por‐2TV‐C₆₀) and tetrad molecules ((Por)₂‐2TV‐C₆₀), which incorporated C₆₀ and one or two porphyrin molecules that were covalently linked through a phenylethynyl‐oligothienylenevinylene bridge, were synthesized. Their photodynamics were investigated by fluorescence measurements, and by femto‐ and nanosecond laser flash photolysis. First, photoinduced energy transfer from the porphyrin to the C₆₀ moiety occurred rather than electron transfer, followed by electron transfer from the oligothienylenevinylene to the singlet excited state of the C₆₀ moiety to produce the radical cation of oligothienylenevinylene and the radical anion of C₆₀. Then, back‐electron transfer occurred to afford the triplet excited state of the oligothienylenevinylene moiety rather than the ground state. Thus, the porphyrin units in (Por)‐2TV‐C₆₀ and (Por)₂‐2TV‐C₆₀ acted as efficient photosensitizers for the charge separation between oligothienylenevinylene and C₆₀.     

Structure‐Dependent Photoinduced Electron Transfer in Fullerodendrimers with Light‐Harvesting Oligophenylenevinylene Terminals

Oligophenylenevinylene (OPV)‐terminated phenylenevinylene dendrons G1 – G4 with one, two, four, and eight “side‐arms”, respectively, were prepared and attached to C₆₀ by a 1,3‐dipolar cycloaddition of azomethine ylides generated in situ from dendritic aldehydes and N‐methylglycine. The relative electronic absorption of the OPV moiety increases progressively along the fullerodendrimer family C₆₀G1 – C₆₀G4 , reaching a 99:1 ratio for C₆₀G4 (antenna effect). UV/Vis and near‐IR luminescence and transient absorption spectroscopy was used to elucidate photoinduced energy and electron transfer in C₆₀G1 – C₆₀G4 as a function of OPV moiety size and solvent polarity (toluene, dichloromethane, benzonitrile), taking into account the fact that the free‐energy change for electron transfer is the same along the series owing to the invariability of the donor–acceptor couple. Regardless of solvent, all the fullerodendrimers exhibit ultrafast OPV→C₆₀ singlet energy transfer. In CH₂Cl₂, the OPV→C₆₀ electron transfer from the lowest fullerene singlet level (¹C₆₀*) is slightly exergonic (ΔG_CS≈0.07 eV), but is observed, to an increasing extent, only in the largest systems C₆₀G2 – C₆₀G4 with lower activation barriers for electron transfer. This effect has been related to a decrease of the reorganization energy upon enlargement of the molecular architecture. Structural factors are also at the origin of an unprecedented OPV→C₆₀ electron transfer observed for C₆₀G3 and C₆₀G4 in apolar toluene, whereas in benzonitrile, electron transfer occurs in all cases. Monitoring of the lowest fullerene triplet state by sensitized singlet oxygen luminescence and transient absorption spectroscopy shows that this level is populated through intersystem crossing and is not involved in photoinduced electron transfer.     

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.     

Transient Absorption Spectral characterization of Electron Transfer between Fullerenes（C60／C70）and N,N,N’，N’—Tetra（p—methylphenyl）—4,4’—diamino—1,1’—diphenyl Sulphide（TPDAS）

In search of new systems with a photoexcited redox pair which exhibits a strong and stable photoinduced absorption band to understand the photophyscial and photochemical properties of electron transfer between fullernes (C60/C70) and organic donor[N,N,N’，N’-tetra(p-methylphenyl)-4,4’-diamino-1,1’-diphenyl sulphide(TPDAS)],we studied characteristic absorption spectra in the near-IR region obtained from 532nm nanosecond laser flash photolysis of a mixture of the fullerenes (C60/C70) and TPDAS in polar solvents.When fullerenes (C60/C70)were photoexcithed,the rise of the radical anion of fullerenes (C60/C70)with the rapid decay of their excited triplet states were observed in benzonitrile.It can be deduced that the electron transfer reaction does take place from TPDAS to excithed triplet state of rullerens(C60/C70).The rate consants(ket)and quantum yiekls(φet) of this process have been also evaluated.     

A Supramolecular [10]CPP Junction Enables Efficient Electron Transfer in Modular Porphyrin–[10]CPP⊃Fullerene Complexes

Efficient photoinduced electron transfer was observed across a [10]cycloparaphenylene ([10]CPP) moiety that serves as a rigid non‐covalent bridge between a zinc porphyrin and a range of fullerenes. The preparation of iodo‐[10]CPP is the key to the synthesis of a porphyrin–[10]CPP conjugate, which binds C₆₀, C₇₀, (C₆₀)₂, and other fullerenes (K_A>10⁵ m ^?1). Fluorescence and pump–probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge‐separated states. The advantage of this approach towards electron donor–acceptor dyads is evident in the case of dumbbell‐shaped (C₆₀)₂, which gave intricate charge‐transfer behavior in 1:1 and 2:1 complexes. These results suggest that [10]CPP and its cross‐coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.