Triplet State Characteristics Research Articles

Activity-Based Photosensitizers with Optimized Triplet State Characteristics Toward Cancer Cell Selective and Image Guided Photodynamic Therapy.

Activity-based theranostic photosensitizers are highly attractive in photodynamic therapy as they offer enhanced therapeutic outcome on cancer cells with an imaging opportunity at the same time. However, photosensitizers (PS) cores that can be easily converted to activity-based photosensitizers (aPSs) are still quite limited in the literature. In this study, we modified the dicyanomethylene-4H-chromene (DCM) core with a heavy iodine atom to get two different PSs (DCMO-I, I-DCMO-Cl) that can be further converted to aPS after simple modifications. The effect of iodine positioning on singlet oxygen generation capacity was also evaluated through computational studies. DCMO-I showed better performance in solution experiments and further proved to be a promising phototheranostic scaffold via cell culture studies. Later, a cysteine (Cys) activatable PS based on the DCMO-I core (DCMO-I-Cys) was developed, which induced selective photocytotoxicity along with a fluorescence turn-on response in Cys rich cancer cells.

Quenching of meso-tetramethylpyridyl porphyrin excited triplet state by inorganic salts: Exciplex formation

The effects of LiCl, LiBr, LiI, NaCl, NaBr, NaI, KCl, KBr and KI salts on the excited triplet state characteristics of meso-tetramethylpyridyl porphyrin (TMPyP) in aqueous solutions were studied. It was demonstrated that inorganic salts in concentrations below 0.1 M effectively quench the TMPyP T1* triplet state. The logarithm of the quenching constant decreases linearly with the increase of the salt anion ionization potential, the effect of the cation nature being negligible. Triplet state quenching was explained by partial electron transfer from the salt anion to TMPyP in its triplet state (exciplex formation). This hypothesis was confirmed by the phosphorescence detection. The analysis of the singlet oxygen phosphorescence at λ = 1270 nm demonstrates that the quantum yield of the singlet oxygen increases in the presence of salts. Besides, the characteristic time of the singlet oxygen formation and its lifetime increase in the salt presence. These effects occur, probably, via energy transfer from the exciplex to the oxygen molecule. Moreover, a new phosphorescence at λ = 1200 nm appeared in the presence of salts has been observed, which we associate with that of the exciplex.The exciplex formation is accompanied by reversible short-lived optical absorption. On the other hand, salts in concentrations below 0.1 M do not induce any significant changes in the TMPyP S0→S1* absorption spectrum. Moreover, due to complete dissipation of the exciplex the salts in these concentrations do not influence the TMPyP photostability.

Effects of NaCl upon TPPS 4 triplet state characteristics and singlet oxygen formation

The quantum yield ( φ T) and lifetime ( τ T) of the triplet state (T) of water-soluble meso-tetrasulphonatophenyl porphyrin (TPPS 4) and the kinetic profile and quantum yield ( φ O 2 1 ) of the singlet oxygen 1O 2, produced due to the energy transfer from T to molecular oxygen, were investigated for biprotonated (pH 4.0) and non-protonated (pH 7.0) TPPS 4 forms as a function of the NaCl concentration. The study was performed with the help of flash-photolysis technique compared with the data obtained by optical absorption spectroscopy. The 1O 2 characteristics were monitored by kinetics and spectrum of its infrared phosphorescence. As shown, for biprotonated TPPS 4 the addition of NaCl reduces both φ T and τ T due to two processes: “quenching” by Na + and/or Cl − ions and successive formation of H and J TPPS 4 aggregates. The triplet state formation for the porphyrin J aggregates was detected. For non-protonated TPPS 4, no aggregation in the presence of salt occurs and the observed reduction of φ T and τ T was due to the interaction with Na + and/or Cl − ions. The reduction of φ T was accompanied by the simultaneous reduction of ( φ O 2 1 ) . No NaCl effects on the quenching constant of T by O 2 and on the 1O 2 lifetime were observed.

The Triplet State of a N-Phenylphthalimidine with High Intersystem Crossing Efficiency: Characterization by Transient Absorption Spectroscopy and DNA Sensitization Properties

The detailed triplet state characteristics of 2-(4-acetylphenyl)isoindolin-1-one (kINP), a N-phenylphthalimidine (PPI) derivative, have been studied in fluid solution at room temperature. The attac...

Triplet-State Characteristics and Photoionization Behavior of 2,2‘- and 4,4‘-Biphenyldiol Studied by 248 nm Laser Flash Photolysis in Aqueous Solutions

Triplet-state characteristics and the photoionization behavior of 2,2'- and 4,4'-biphenyldiol have been investigated in aqueous solutions using the 248 nm nanosecond laser flash photolysis (LFP) technique. For 2,2'-biphenyldiol, the neutral form of the triplet state is mainly produced following the laser excitation in aqueous solutions for the pH conditions in which the ground state of the diol exists in its neutral form (pK a G = 7.5). In aqueous alkaline solutions, in which the diol exists in its monoanionic form, photoexcitation leads to the formation of the anionic form of the triplet state along with phenoxyl radical and hydrated electron (e a q - ), Under similar conditions, the 4,4'-biphenyldiol behaves somewhat differently. Unlike 2,2'-biphenyldiol, the LFP of its 4,4'-analogue not only produces the neutral form of the triplet state but also gives phenoxyl radical, even when the ground state of the diol exists in its neutral form in solution (pK a G = 9.4). In alkaline solutions (pH ≥ 11), though, like its 2,2'-analogue, the 4,4'-biphenyldiol also produces the anionic form of its triplet state along with the phenoxyl radical and e a q , the photoionization (PI) yield is higher for 4,4'-biphenyldiol. Further, it is interesting to observe that the mechanism of PI in the two diols is different, monophotonic for the 4,4'-analogue and biphotonic for the 2,2'-analogue. The differences in the above results on the two diols have been explained on the basis of the presence and absence of intramolecular hydrogen bonding in the diol molecules.

Triplet state characteristics of 2,2 ′- and 4,4 ′-biphenyldiols studied by 248 nm nanosecond laser flash photolysis

Triplet state characteristics of 2,2 ′- and 4,4 ′-biphenyldiols have been investigated in different organic solvents using 248 nm nanosecond laser flash photolysis technique. While for 2,2 ′-biphenyldiol, the triplet state of the molecule is produced as the only transient, for 4,4 ′-biphenyldiol, some phenoxyl radicals are also formed along with the triplet state following the laser excitation. Triplet quantum yields of 2,2 ′-biphenyldiol in different solvents are seen to be much lower than those of 4,4 ′-biphenyldiol. The differences in the laser flash photolysis results of the two diols have been explained on the basis of the presence and the absence of intramolecular hydrogen bonding in the two molecules.

Studies on the radiolytically produced transients of neutral red: triplet and reduced radicals.

The spectral and kinetic properties of reduced radicals and the triplet state of neutral red (NR), a phenazine-based dye, have been investigated using pulse radiolysis technique. A mixed water-isopropanol-acetone solvent has been used to study the reduced radicals of NR for a wide pH range of about 1-13, due to limitation of solubility of the dye in aqueous solutions particularly above pH 8. From pH-dependent absorption studies it has been established that the reduced radicals of NR can exist in four different prototropic forms in solution. Three pKa values for the corresponding prototropic equilibria have been estimated. The formation and decay rate constants of reduced radicals have also been measured. The triplet state characteristics of the dye have been investigated in neat benzene solutions, both in the presence and in the absence of triplet sensitizers. The T1-->Tn absorption spectrum and decay kinetics of the triplet state have been measured. The triplet state energy (ET) of NR in benzene have been estimated to be within 36-42 kcal mol-1, using an energy transfer method.

Photophysical studies on the interaction of two water-soluble porphyrins with bovine serum albumin. Effects upon the porphyrin triplet state characteristics

The interaction of two metal-free water soluble porphyrins (PPh): meso-tetrakis ( p-sulfo-natophenyl)porphyrin (TPPS 4) and meso-tetrakis(4- N-methyl-pyridiniumyl)porphyrin (TMPyP), with bovine serum albumin (BSA) was investigated in the pH range from 4.0 to 8.5 using the flash-photolysis technique in comparison with results obtained by optical absorption, fluorescence and resonance light scattering. It was found that in the presence of BSA, TPPS 4 can exist in aqueous solutions as free monomers, aggregates and/or monomers bound to a single BSA molecule and monomers inside the BSA aggregates, while TMPyP does not form aggregates at binding. Binding to BSA transforms the profile of the triplet decay curve from monoexponential to biexponential form with the component lifetimes and relative amplitudes depending on binding characteristics. The triplet lifetime of a bound porphyrin monomer is longer than that of a free one. The aggregation of TPPS 4 observed at [TPPS 4]/[BSA] > I reduces the T-T absorption since the lifetimes of the aggregate excited states are very short and/or quantum yield of the aggregate triplet state is very low. The porphyrin binding to BSA reduces the quenching constants of the porphyrin triplet states by molecular oxygen due to obstacles produced by binding. This effect is especially pronounced for the porphyrin molecules located inside BSA aggregates formed around the porphyrin molecules in excess BSA.

Non-planarity and its implications on triplet state characteristics of basket handle porphyrins

The influence of non-planarity in the porphyrin ring on the triplet state characteristics of free base and Zn(II) derivatives of basket handle porphyrins is investigated by triplet ESR. The deviation of the zero-field splitting parameter, D, from planar H 2TPP or ZnTPP is dependent on the degree of non-planarity and increases as the non-planarity increases. The electron spin polarization (ESP) pattern for most derivatives remains the same as observed for H 2TPP or ZnTPP. However, MSICI 8, PSIBr 8, ZnMSIICI 8 and Znbutyl II show different ESP patterns, suggesting a redirection of the spin sublevel activity in these isomers. The ESP pattern for PSIBr 8 is temperature dependent (eeaeaa at −160°C and eeeaaa at −106°C). The calculated structure using molecular mechanics reveals maximum deformation in these isomers which in turn governs the population and decay of the triplet sublevels. The structures indicate a different orientation of bridging phenyl groups in PSIBr 8 and MSICl 8 with respect to the porphyrin plane.

Photoexcited triplet ESR studies on water-soluble thiaporphyrins

Triplet state characteristics of monomer and dimer of two core modified thiaporphyrins (STPPS and S2TPPS) are reported. Introduction of heavy sulfur atom(s) into the porphyrin core does not alter the zero-field splitting parameters significantly and the ESP pattern remains the same as in analogous H2TPPS. This is possibly due to similarities in the structures of the porphyrin core of STPPS, S2TPPS and H2TPPS. However, there is a strong dimerization effect on the D value similar to those observed for dimerization of H2TPPS.

Molecular Structures and Magnetic Properties of Strongly Antiferromagnetically Coupled Binuclear Copper(II) Complexes [CU2REP(μ-X)(Y)2

The molecular structures of binuclear copper(II) complexes [Cu2REP(μ-OH)(ClO4)2] (4) and [Cu2REP(μ-Cl)Cl2] (5), in which REP = deprotonated 2,6-bis(1′-(4′-(2″-pyridyl)-2′-thiabutyl))-4-methylphenol, have been characterized by single-crystal X-ray diffraction. The former crystallizes in the triclinic space group Pl with a = 10.156(3), b = 12.631(3), c = 25.128(10) A, α = 92.03(3), β = 96.84(3), γ = 108.02(2),° and Z − 2. Complex 5 crystallizes in the monoclinic space group C2/c with a = 12.166(2), b = 11.825(2), c = 18.240(4) A, β = 100.97(2)°, and Z =4. All copper ions are pentacoordinated with ligation to a sulfur, a nitrogen, and the bridging phenolato oxygen of the REP ligand, the exogenous bridge, and a counteranion. The coordination geometry of each copper of the binuclear copper sites is square pyramidal in both 4 and 5. Magnetic susceptibility measurements in the temperature range 6–300 K reveal a strong antiferromagnetic spin exchange in 5 (exchange integral 2J = −460 cm−1). A diamagnetic behavior is observed for 4 according to a similar cryomagnetic investigation. The diamagnetism of 4 is further confirmed by measurements of magnetic susceptibility through Evan's method at room temperature. Complex 4 has no EPR signal. The powder EPR spectrum of 5 shows the typical triplet state characteristics with Δm = ±1 transitions at g = 2.15 and a weaker Δm = 2 transition at half field with g = 4.24.

Laser photolysis of laser dyes and the influence of triplet quenchers

Laser photolysis method for direct measurement of the triplet state characteristics of some of the most efficient laser dyes is reported. Triplet lifetimes τ T and intersystem crossing constants K ST for some xanthene and oxazine dyes in different solvents are presented. The positive effect of cyclo-octatetraene and diphenylbutadiene on laser properties is attributed to the reduction in the intersystem crossing constant and not to the quenching of the triplet state of the dye molecule.

Triplet state characteristics and singlet oxygen generation properties of anthracyclines

The triplet states of adriamycin (Ad), daunomycin (D) and two daunomycin analogues, daunomycinone (Dc) and daunomycin N-trifluoroacetamide (DAc), have been studied using laser flash photolysis and pulse radiolysis techniques. Triplet lifetimes, molar absorption coefficients, energy levels and quantum yields have been obtained for Dc and DAc, and estimated for D and Ad. Time-resolved near-infrared singlet oxygen luminescence measurements have been carried out on D, Ad and 5-iminodaunomycin (5-ID) in 2H2O solution and Dc in benzene solution at room temperature. Singlet oxygen quenching by the water-soluble anthracyclines was observed and a second-order rate constant of approx. 10(8) M-1.s-1 obtained. Electron spin resonance experiments have demonstrated that D photoexcited at lambda less than or 365 nm gives rise to singlet oxygen as shown by its reaction with 2,2,6,6-tetramethyl-4-piperidone to give the corresponding nitroxyl radical. Although all the anthracyclines studied have the ability to photosensitize the formation of singlet oxygen, the quantum yields are very low (phi delta approximately 0.02-0.03), suggesting that these anthracyclines would be poor photodynamic sensitisers.

Singlet oxygen yields and radical contributions in the dye-sensitised photo-oxidation in methanol of esters of polyunsaturated fatty acids (oleic, linoleic, linolenic and arachidonic).

Abstract— The triplet state characteristics (spectrum, lifetime and quantum yield) for four dye sensi tisers [methylene blue (MB), erythrosin (ER), haematoporphyrin (HP) and riboflavin (RF)] were determined in methanol by laser flash photolysis and singlet oxygen yields (0.60 to 0.48) from time‐resolved measurements of the 1270 nm near infrared emission. The reaction of singlet oxygen with four long chain unsaturated phenyl esters [oleate (18: 1), linoleate (18: 2), linolenate (18: 3) and arachidonate (20: 4)] was followed quantitatively using the singlet oxygen luminescence technique and also, after continuous420–700 nm irradiation, by HPLC and other analysis of the isomeric product monohydroperoxides. The overall quantum yield of photooxidation (∼10‐2) was shown to be consistent with the observed singlet oxygen quenching constants(2–12 times 104 dm3 mol‐1 s‐1) for the four esters studied and the singlet oxygen lifetime in methanol (τ∼ 9 μs). The isomer product distribution was interpreted in terms of a dual singlet oxygen and radical mechanism, the radical contribution increasing with sensitiser in the order ER = MB < HP ≪ RF, but also showing some dependence on substrate unsaturation. Evidence is presented for singlet oxygen quenching by MB and RF (kO= 1.6 and 6.0 times 107 dm3 mol‐1 s‐1) and for the accelerated photobleaching of the dye sensitisers in the presence of the unsaturated esters.

Zeeman effect in complex molecules in solid solutions with laser T 1 → S 0 excitation. New possibilities for investigation of spin—lattice relaxation

The main peculiarities of Zeeman-effect in phosphorescence spectra of randomly oriented molecular systems under selective T 1→S 0 excitation are investigated. On this basis a new method of measuring triplet state characteristics and spin—lattice relaxation rates in solid solutions is proposed. The results of Zeeman-effect investigations on 5-bromo-acenaphtene in ethanol and butylbromide at magnetic fields 10–50 kG at helium temperatures are given as an example. At low fields the deviation from Boltzmann equilibrium in the spin system of the molecule is observed and the rates of spin—lattice relaxation are determined.