A study on the energy transfer and migration in the molecules of polymeric triplet sensitizers: (2) A study on delay fluorescence and polarization spectra

The triplet energy migration of polymers and copolymers of vinyl benzophenone (VBP) and vinyl naphthalene (VN) has been studied by measuring delayed fluorescence and polarization spectra in glassy dilute solution at 77 K. Strong delayed fluorescence of PVN proves the existence of triplet energy migration and T-T annihilation in the polymer chain. Efficient intersystem crossing of “BP” and efficient energy migration and transfer between chromophores along the polymer chain result in the absence of delayed fluorescence for copolymer P (VN-VBP) studied in this work. The order of benzophenone phosphorescence intensity: BP>Co (VBP-St)>PVBP indicates the T-T annihilation decreasing the phosphorescence of PVBP. Fluorescence and phosphorescence polarization data of polymers are smaller than that of their model compounds. It is evident that energy migration exists in the polymer chain.     

Triplet-triplet absorption spectra of phenanthrene and azaanalogues

Triplet-triplet (T-T) absorption spectra of phenanthrene and several azaanalogues were measured in the spectral range from 25000 to 17000 cm⁻¹ at 83 K. For the first time a vibrational structure of the main band systems in the T-T spectra could be detected. The vibrational modes producing these progressions are associated with the lower T₁ state. The assignment of the vibrational structure to the T₁ state has been confirmed by computation of the T-T spectra with the help of a lineshape function. Furthermore, in the spectra of the azaanalogues an additional absorption band appears which is assigned to a T-T transition from the T₂ state.     

Effect of macromolecules and Triton X-100 on the triplet of aggregated chlorophyll in aqueous solution

Chlorophyll a (Chla) in aqueous solution (2-6% acetone) is present as mono- and dihydrated aggregated forms which are characterized by specific ground state absorption spectra. The amount of dihydrated form is larger in the presence of macromolecules, such as bovine serum albumin (BSA), lysozime and polyvinyl alcohol (PVA), increasing from BSA to lysozime and PVA. Chla in aqueous acetone with and without macromolecules is characterized by low fluorescence and the absence of triplet-triplet (T-T) absorption. The ratio of dihydrated to monohydrated forms is significantly influenced by triton X-100. For lower triton X-100 concentrations, i.e. smaller than the critical micelle concentration of 0.26 mM (cmc), dihydrated forms are converted into monohydrated in both aqueous acetone and the presence of BSA or lysozime. In the presence of PVA dihydrated forms appeared to be resistant to triton X-100 action. Moreover, for triton X-100 concentrations of 2-3 times higher than cmc the amount of these forms is increased with time. T-T absorption of both mono- and dihydrated Chla aggregates was not detected in the presence of [triton X-100] < cmc. The lack of T-T absorption in aqueous acetone solution as well as in the presence of macromolecules implies that the triplet lifetime of the chlorophyll aggregates is short (tauT<10 ns) and/or the quantum yield of intersystem crossing is small (<5 x 10(-3)). The Chla monomers start to be formed as solubilized in the micelle for [triton X-100] larger than cmc, showing substantial fluorescence and T-T absorption.     

Triplet-triplet absorption spectra of meso-tetraphenyl-2,3-tetranaphtho-2,3-tetraphenanthroporphins

Flash photolysis has been used to measure triplet-triplet (T-T) absorption spectra of meso-tetrapheny1-2,3-tetranaphthorphin and its zinc complex, and also zinc complexes of two isomers of meso-tetrapheny1-2,3-tetraphenanthrenopurphin. An analysis has been made of the inf Iuence of structural changes on the T-T absorption spectra.Institute of Physics, Academy of Sciences of the Belorussian SSR, Minsk. Scientific-Research Institute of Organic Intermediates and Dyestuffs, Moscow. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 1, pp. 105–108, January–February, 1991. Original article submitted February 24, 1989.     

Application of radiochemical neutron activation and flame atomic absorption spectrometry for the determination of manganese in blood

The triplet-triplet absorption spectra of various aromatic compounds in benzene solution were studied by pulse radiolysis. It has been found that methylation of naphthalene characteristic absorption band in this group of compounds at 430±10 nm (naphthalene, 2-methylnaphthalene, 2,6-dimethylaphthalene, anthracene, phenanthrene, pyrene and fluorene); new bands appeared with phenanthrene and pyrene at 495 and 525 nm respectively. The decay remains of the first order in the whole group with similar rate constant values. Diphenyl and 1,1-dinaphthyl show significant changes in their T-T spectra in comparison with the preceding group of compounds. T-T spectrum of o-terphenyl differs significanly from those of p-and m-isomers, which can be caused by greater overlapping of electron orbitals in o-isomer molecule. Aromatic ketones show a complex picture both in spectra and decay kinetics.     

Photophysical processes in dimers of thiacarbocyanine cations

The results of quantum-chemical calculations of absorption, fluorescence, and induced T-T absorption spectra and the rate constants of photophysical processes for the monomer and dimers of the 3,3′-diethylthiacarbocyanine cation are presented. It has been shown that the formation of the dimers leads to a substantial reduction in the efficiency of the radiative pathways and enhancement of the efficiency of the non-radiative pathways of deactivation of the fluorescent state, thereby resulting in a decrease in the quantum yield of fluorescence. The fluorescence quantum yield depends in this case on the relative orientation of the molecules in the dimer with respect to each other. The calculation results satisfactorily describe experimental data on the spectral and luminescent properties of the dimers of the 3,3′-diethylthiacarbocyanine cation and their photophysical processes.     

Anisotropy of the T-T absorption spectra of naphthalene and phenanthrene

The naphthalene absorption in the spectral region of 3500–4100 Å consists of two perpendicularly polarized band systems. This can be shown by polarization measurements. The arguments given do not allow a decision as to whether or not the short axis polarized band is the ³A_g⁻ ← ³B_iu⁺ transition or an induced vibronic band of the ³B_3g⁻ ← ³B_iu⁺ transition generated by a b_3g vibration mode. The T-T polarization of phenanthrene as a function of the excitation wavenumber is quantitatively compared with the equivalent S₁ ← S₀ fluorescence polarization. There is a good agreement between the calculated and the measured curve.     

Stokes and anti-Stokes Raman scattering of 5H-dibenzo(a,d)cyclohepten-5-ol

The ultraviolet absorption and emissions as well as Stokes and anti-Stokes Raman scatterings of spectroscopically pure 5H-dibenzo(a,d)cycloheptene-5-ol were investigated by flash and laser-flash photolysis technique in solution at room temperature and at 77K. The whole spectrum, absorption, excitation, prompt and delayed fluorescence, T-T absorption spectra were recorded photographically and photoelectrically in the ultraviolet and visible region and phosphorescence spectrum, Stokes, anti-Stokes scatterings were recorded at 77K.     

Effects of temperature on the triplet behavior of the styrylphenanthrene isomers

The properties of the triplet state of five styrylphenanthrene (StPh) trans isomers were studied in 2-methyltetrahydrofuran (MTHF) as a function of temperature. At room temperature the T-T absorption was observed only for 4- and 9-StPh, while under these conditions 1-, 2-, and 3-StPh have too low a quantum yield of triplet formation (Φ_T <0.02); their T-T absorption spectra were obtained at low temperature. Φ_T of 1- and 2-StPh increases more than tenfold on going from 293 to 77 K, and the triplet lifetime (τ_T) increases by four orders of magnitude and approaches values of 5–40 ms at 77 K. The change in τ_T is explained in terms of an equilibrium between trans and perpendicular (perp) conformations of the lowest triplet state in fluid solution and temperature and viscosity effects on the trans → perp rotation. Evidence is presented for the existence of two conformeric trans triplet states of 3-StPh at 77 K. Semi-empirical calculations were performed to obtain the energy of the triplet state, the wavelengths of several T-T absorption maxima (λ_T), and the oscillator strength. The calculated λ_T values coincide with those measured in n-hexane.     

The radicals formed by photoinduced electron transfer from hypocrellins to electron acceptors

The photoinduced electron transfer from excited singlet and triplet states of hypocrellins to three electron acceptors, namely, methyl viologen chloride (MV), tetrachloro-p-benzoquinone (TCQ) and 2,3-dichloro-5,6-dicyan-p-benzoquinone (DDQ), has been investigated by fluorescence and time-resolved transient absorption spectra. In acetonitrile solution, DDQ and TCQ quenched the fluorescence and T-T absorption of hypocrellins (HA and HB) efficiently, while neither fluorescence nor T-T absorption of them could be quenched by MV. The quenching resulted from the electron transfer between excited hypocrellins and the electron acceptors was controlled by diffusion. The rate constants of electron transfer from excited singlet and triplet of HA to DDQ are 9.20×10¹⁰ dm³ mol^?1 s^?1 and 1.28×10⁹ dm³ mol^?1 s^?1, respectively. The transient absorption spectra of the formed radical cations of hypocrellins are reported.     

Photochemistry of a crown ether styryl dye adsorbed on silica gel and in acetonitrile solution: a comparative flash photolysis study

The photochemical behaviour of a photochromic crown ether styryl dye (BOB) adsorbed on silica gel has been found by a steady-state technique to be similar to that observed in a fluid solution of high polarity. The intermediate spectra obtained by diffuse reflectance laser flash photolysis of BOB on silica gel in a nitrogen atmosphere have been preliminarily attributed to the triplet-triplet (T-T) absorption of BOB and the absorption of BOB cation radicals. For comparison, the absorption spectrum of BOB triplets with a lifetime of ∼0.8 μs in acetonitrile solution has been obtained using biphenyl as a sensitizer.     

Excited singlet yield in T-T annihilation, a comparative study of naphthalene and anthracene in solution

A method based on the study of both triplet absorption and delayed fluorescence (DF) decays after flash excitation has been developed to determine DF yields. Values of the excited singlet yield in the T-T annihilation process have been obtained for naphthalene and anthracene in solution at room temperature by application of this method. Triplet extinction coefficients and annihilation rate constants for these compounds were also determined. Excited singlet generation is the predominant annihilation channel for naphthalene whereas it is only of minor importance for anthracene. The difference in DF yields is ascribed to differences between these aromatics with respect to the efficiencies of the annihilation channels leading respectively to excited singlet and triplet states. The higher rate of excited singlet formation for naphthalene is qualitatively accounted for by considering the possibility of radiationless transitions from the bimolecular states formed in T-T interaction towards an upper excimer singlet state.     

Thermodynamic scaling of polymer dynamics versus T-T(g) scaling

A thermodynamic scaling law for the relaxation times of complex liquids as a function of temperature and volume has been proposed in the literature: τ(T,V) = f(TV(γ)), where γ is a material-dependent constant. We test this scaling for six materials, linear polystyrene, star polystyrene, two polycyanurate networks, poly(vinyl acetate), and poly(vinyl chloride), and compare the thermodynamic scaling to T-T(g) scaling, where τ = f(T-T(g)). The thermodynamic scaling law successfully reduces the data for all of the samples; however, polymers with similar structures but different glass transition (T(g)) and pressure-volume-temperature (PVT) behavior, i.e., the two polycyanurates, cannot be superposed unless the scaling law is normalized by T(g)V(g) (γ). On the other hand, the T-T(g) scaling successfully reduced data for all polymers, including those having similar microstructures. In addition, the T-T(g) scaling is easier to implement since it does not require knowledge of the PVT behavior of the material. The relationship between T(g)V(g) (γ)∕TV(γ) and T-T(g) scaling is clarified and is found to be weakly dependent on pressure.     

Triplet-triplet absorption of naphthalocyanines and related compounds

Flash photolysis has been used to measure triplet-triplet (T-T) absorption spectra of Pd phthalocyanine, Zn-l,2-naphthalocyanine, Pd-tetra-6-tert-butyl-2,3-naphthalocyanine, and Zn-tetra-2,3-benzo[g]quinoxalinoporphyrazine. On the basis of the results obtained in this work, together with literature data, an analysis has been made of the influence of annelation in a series of metallocomplexes of tetraazaporphin and the influence of aza-substitution in tetraarenoporphins on the T-T-absorption spectra.Translated from Teoreticheskaya i Éksperimental'naya Khimiya Khimiya, Vol. 26, No. 5, pp. 585–590, September–October, 1990.     

Photophysical properties and photochemical rearrangement of single crystal salicylideneaniline in solution

Salicylideneaniline originally crystallized from a solution has lemon yellow color. Irradiation with near ultraviolet causes the color change from yellow to red. The red state changes spontaneously back to yellow in 2ms. This change is accelerated by visible light. Kinetic data are reported in the temperature range between 10 and 60 degrees C, for the dark fading reactions of the colored isomers formed by the near ultraviolet irradiation. Observed the decay kinetics was first order reactions. Activation energies and entropies of activation are reported for ethanol. The observation of T-T absorption and emission were complicated due to the colored isomer formation during the optical pumping.     

Context-dependent photodimerization in isolated thymine-thymine steps in DNA

The effect of 280 nm irradiation on a family of synthetic DNA hairpins possessing an alkane linker connecting a six-base pair stem having a single T-T step located at different positions within the hairpin has been investigated. A single adduct assigned to the product of 2+2 dimerization is obtained except in the case of a T-T step located adjacent to the linker, in which case both 2+2 and 6-4 adducts are obtained. The efficiency of dimerization is similar for three hairpins having a T-T step located within the duplex interior. Lower efficiency is observed for a T-T step located at the open end of the hairpin and in T overhangs, whereas higher efficiency is observed for the T-T step adjacent to the linker and in a single T bulge. The context-dependence of dimerization efficiency is discussed.     

Structural and dynamic variations in DNA hexamers containing T-T and F-F single and tandem internal mispairs

Molecular dynamics simulations of double-helical DNA oligomers have been performed to investigate differences in the structure, dynamics, and hydration of F-F and T-T mispairs. Hexamers containing F-F pairs were found to be more dynamic, especially in the region of the mispair itself. This dynamic variability derives from greater flexibility of F-F pairs. The T-T mispairs, on the other hand, were found to be comparatively tightly bound as wobble pairs. The major and minor groove edges of the T-T pairs were observed to be solvated at exposed carbonyl positions by at least one water molecule, while F-F pairs lacked solvating waters. Stacking interactions were nearly identical for T-T and F-F pairs, leading to similar average structures, even though F stacking was more dynamically variable. Solvation differences between F-F and T-T therefore support the steric exclusion model for nucleotide incorporation in DNA replication. Large differences in the orientation of minor groove functional groups, in addition to differences in solvation, further rationalize why F bases present during DNA extension events induce stalls. Two novel nucleotides are proposed to further elucidate minor groove interactions of DNA with polymerase molecules.Electronic Supplementary Material This Material consists of equilibration protocol, plots of center-of-mass stacking, water radial distribution functions, helical parameter dynamics, and dynamics data for a control AT sequence. Supplementary material is available in the online version of this article at Contribution to the Jacopo Tomasi Honorary Issue     

Transient absorption spectra of 2-hydroxybenzophenone photostabilizers

Transient absorption spectra (400–600 nm) of 2-hydroxybenzophenone and the methyl methacrylate copolymer of 2-hydroxy, 3-allyl, 4,4'-dimethoxybenzophenone following 355 nm excitation (7–480 ps delay) are reported. A short-lived, 435 nm transient (τ ≈ 10 ps in CH₂Cl₂) for both molecules is assigned to the lowest excited singlet before internal proton transfer. Weaker, broad T-T absorption is observed after 480 ps.     

Photophysical properties of a 1,2,3,4,5,6-hexasubstituted fullerene derivative

The photophysical properties of a novel 1,2,3,4,5,6-hexasubstituted fullerene derivative (1) are examined in this study. In addition to the ground state absorption spectrum of 1, we report its triplet-triplet absorption spectrum and molar extinction coefficient (Deltae(T-T)), as well as the triplet quantum yield (PhiT), lifetime (tauT), and energy (ET). The saturation of a single six-member ring on the fullerene cage results in significant changes in the triplet state properties as compared to that of pristine C60. The triplet-triplet absorption spectrum shows a hypsochromic shift in long wavelength absorption, and both the triplet state lifetime and the triplet quantum yield are decreased. The triplet energy was found to be similar to that of C60. In addition, the quantum yield (PHI(delta)) of singlet oxygen generated by 1 was calculated and is found to be significantly less than in the case of C60.     

meso-苯基四苯并卟啉的合成和光谱性能研究(Ⅱ)

本文将meso-苯基四苯并卟啉锌(Zn-P_nTBP n=1～4)在酸性条件下脱锌,获得了不含金属离子的meso-苯基四苯并卟啉(H₂P_nTBP n=1～4)。研究了它们的吸收光谱、荧光光谱及在溶液状态下的瞬态光谱特性,并对照相应的锌卟啉,讨论了两者之间的光谱差异。