Laser Kinetic Spectroscopy Research Articles

Photoprocesses in Bis-Diethylamino Derivatives of 1,4- and 1,3-Distyrylbenzene.

The photoprocesses of diethylamino derivatives of 1,4- and 1,3-distyrylbenzenes in MeCN were studied using absorption, luminescence, 1H NMR, and laser kinetic spectroscopy. Compounds 1 and 2 undergo intersystem crossing to the triplet state and exhibit delayed fluorescence. It was concluded that dye radical anions and radical cations are formed upon dismutation of the triplet state in the presence of an electron donor or acceptor. Quantum mechanical calculations for the structures of diethylamino distyrylbenzenes in the ground and excited states were carried out, making it possible to establish the structures of isomers and the most stable conformers for both compounds.

Single- and Double-Pulse Laser Kinetic Spectroscopy of Indoline Spiropyran

Phototransformations of 6-nitro-8-methoxy-substituted indoline spiropyran in acetonitrile have been studied by laser kinetic spectroscopy (laser photolysis) with single- and double-pulse excitation. The role of the triplet state in the kinetics of photocoloration of spiropyran has been revealed. It has been shown that photochromic transformations of spiropyran involve unstable trans-isomers (conformers) of the open merocyanine form of spiropyran. Data on the transformation kinetics of the trans-isomers are presented.

Molecular Oxygen Migration in Isolated β-Chains of Human Hemoglobin as Revealed by Molecular Dynamics Simulations and Laser Kinetic Spectroscopy

Molecular Oxygen Migration in Isolated β-Chains of Human Hemoglobin as Revealed by Molecular Dynamics Simulations and Laser Kinetic Spectroscopy

Photoprocesses in bis(15-crown-5)-1,3-distyrylbenzene and its complexes with metal perchlorates

Photoprocesses in bis(15-crown-5)-1,3-distyrylbenzene (DSB) and its complexes with barium and lead perchloatewere studied in MeCN by absorption, luminescence, and laser kinetic spectroscopy. The triplet DSB molecules are involved in the degradation of electronic excitation energy, together with fluorescence processes. The most efficient intersystem crossing accompanied by a decrease in the DSB fluorescence quantum yield, occurs for the lead perchlorate complex. Using quantum chemistry methods (DFT and TDDFT), the geometry, structure, and transition energies to the S1 state were calculated for trans- and cis-isomers of DSB in the gas phase and with allowance for the solvent and for 1:1 and 2:2 DSB complexes with barium cation in the ground and excited states. The orbital structures of the 2:2 complexes were calculated by ab initio method, and conclusions were drawn about the possibility of [2 + 2]- photocycloaddition reaction.

Photoconversions of 15-crown-5-containing styryl dye and its complex with barium cation in the presence of cucurbit[7,8]urils

Photophysical processes and photochemical reactions of a 15-crown-5-containing styryl dye of the pyridine series and its complexes with barium perchlorate in water in the absence and in the presence of cucurbit[7,8]urils were studied using absorption, luminescence, and laser kinetic spectroscopy. The trans—cis-photoisomerization, interconversion of the dye to the triplet state, and charge transfer were concluded to occur. The formation of a dye inclusion complex with cucurbit[7,8]urils was established.

Phototransformations of Neutral Red dye in aqueous solutions in the presence of cucurbit[7]uril

Photophysical properties and photochemical transformations of Neutral Red (NR) dye in water in the presence of cucurbit[7]uril (CB7) were studied by absorption, fluorescence, and laser kinetic spectroscopies. Phototransformations of NR involve the triplet state of the dye and the production of NR radical cations and radical anions. The formation of inclusion complexes NR@CB7 was detected. The quantum yield of fluorescence and the efficiency of intersystem crossing to the triplet state increase in the presence of CB7.

Photoprocesses in bis(18-crown-6)-1,3-distyrylbenzene and its complexes with metal perchlorates

Photoprocesses of bis(18-crown-6)-1,3-distyrylbenzene (DSB) and its complexes with barium and lead perchlorates in a MeCN–CH2Cl2 (9:1, v/v) mixture were studied by absorption, luminescence, and laser kinetic spectroscopies. Unlike its strongly conjugated 1,4-isomer, 1,3-derivative shows almost independent behavior of its chromophoric subunits and is capable of phototransformations not observed in 1,4-distyrylbenzenes. Triplet DSB complexes are involved in the radiationless deactivation of the excited state along with the fluorescence processes. The most effective intersystem crossing was observed for the complex with lead perchlorate. The process is accompanied by a drastic decrease in the quantum yield of DSB fluorescence. Quantum chemistry (DFT and TDDFT) is used to calculate the geometric structure and absorption spectra of DSB and its complexes with barium and lead cations and to explain the observed results.

Bis(15-crown-5)-1,4-distyrylbenzene and its complexes with metal perchlorates: photonics and structure

Photoprocesses of bis(15-crown-5)-1,4-distyrylbenzene (DSB) and its complexes with barium and lead perchlorates in MeCN were studied by absorption, luminescence, and laser kinetic spectroscopies. Triplet DSB complexes are involved in the degradation of electronic excitation energy along with the trans—cis-isomerization and fluorescence processes. The most effective intersystem crossing was observed for the complex with lead perchlorate. The process is accompanied by a decrease in the quantum yield of DSB fluorescence and no trans—cis-isomerization is observed in this case. Shifts of spectral bands observed in the absorption and fluorescence spectra and the changes in the band intensities as well as the ability of DSB to form the 2: 2 bisandwich complex with barium perchlorate were explained using the results of quantum chemical calculations.

Photonics of 18-crown-6-containing styryl dye and its complex with cucurbit[7]uril in the presence of lead cation

The photophysical processes and photochemical reactions of 4-[(E)-2-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecyn-18-yl)vinyl]-1-ethylpyridinium perchlorate and its complexes with cucurbit[7]uril in water in the absence and in the presence of lead perchlorate were studied by absorption, luminescence, and laser kinetic spectroscopy. Intersystem crossing to the triplet state and trans—cis-photoisomerization of the dye were established. The formation of an inclusion complex of the dye with cucurbit[7]uril was found.

Photonics of bis(18-crown-6)-1,4-distyrylbenzene and Its complexes with metal perchlorates

Photoprocesses in bis(18-crown-6)-1,4-distyrylbenzene (DSB) and its complexes with potassium, barium, and lead perchlorates have been studied in MeCN solutions by absorption, luminescent, and laser kinetic spectroscopy. The DSB molecules in the triplet state participate in the degradation of electron excitation energy, cis–trans isomerization, and fluorescence. The triplet–triplet absorption spectrum has several maximums in the range of 500–700 nm. The most efficient intersystem crossing to the triplet state is observed for the lead perchlorate complex, which is accompanied by a drop in the fluorescence quantum yield and the absence of trans–cis isomerization.

Photonics of tetramethoxy-1,4-distyrylbenzene

Photonics of tetramethoxy-1,4-distyrylbenzene in MeCN was studied by absorption, luminescence, and laser kinetic spectroscopies. Photoinduced transformations of the compound in question involve cis–trans-isomerization, intersystem crossing, fast and delayed fluorescence, and electron transfer. The ground-state structure and vibrational spectrum, as well as the energies and structures of excited singlet and triplet states were calculated by the DFT/PBE and TDDFT/PBE0 methods. The assignment of vibronic bands in the absorption spectra was made and the energies of corresponding transitions were calculated.

Photoinduced Breaking of the Fe–O2 Bond in Hemoglobin: Dissociation Quantum Yield, Excited Electronic States, and Nonradiative Relaxation Processes

Bimolecular recombination of molecular oxygen with human hemoglobin upon excitation in different spectral ranges is studied by nanosecond laser kinetic spectroscopy. The results obtained are fundamentally different; i.e., rather efficient photodissociation takes place in the case of excitation into the Q-band of the ππ* nature and is practically absent upon excitation into the near-IR band corresponding to the electron transfer from the porphyrin a2u orbital to a mixed orbital formed of the iron d orbital and the free π orbital of molecular oxygen. Analysis of these data, together with data obtained previously using the techniques of nano-, pico-, and femtosecond spectroscopy, allowed us to describe the mechanism and dynamics of the photodissociation reaction and intraheme relaxation processes.

Generation of 8-oxo-7,8-dihydroguanine in G-Quadruplexes Models of Human Telomere Sequences by One-electron Oxidation.

The mechanistic aspects of one-electron oxidation of G-quadruplexes in the basket (Na+ ions) and hybrid (K+ ions) conformations were investigated by transient absorption laser kinetic spectroscopy and HPLC detection of the 8-oxo-7,8-dihydroguanine (8-oxoG) oxidation product. The photo-induced one-electron abstraction from G-quadruplexes was initiated by sulfate radical anions (SO4 ˙- ) derived from the photolysis of persulfate ions by 308nm excimer laser pulses. In neutral aqueous solutions (pH 7.0), the transient absorbance of neutral guanine radicals, G(-H)˙, is observed following the complete decay of SO4 ˙- radicals (~10μs after the actinic laser flash). In both basket and hybrid conformations, the G(-H)˙ decay is biphasic with one component decaying with a lifetime of ~0.1ms, and the other with a lifetime of 20-30ms. The fast decay component (~0.1ms) in G-quadruplexes is correlated with the formation of 8-oxoG lesions. We propose that in G-quadruplexes, G(-H)˙ radicals retain radical cation character by sharing the N1-proton with the O6 -atom of G in the [G˙+ : G] Hoogsteen base pair; this [G(-H)˙: H+ G G˙+ : G] leads to the hydration of G˙+ radical cation within the millisecond time domain, and is followed by the formation of the 8-oxoG lesions.

Phototransformation of Pyridine-Containing Nitrosubstituted Spiropyran in the Presence of Metal Ions

Photocoloration and complexation reactions of pyridine-containing nitrosubstituted spiropyran with terbium, zinc, and lanthanum cations in acetonitrile have been studied using laser kinetic spectroscopy. The triplet state participates in the photocoloration reaction of spiropyran. The complexation reaction is accompanied by a hypsochromic shift of the absorption band and proceeds in the microsecond range with pseudo-first order rate constants of 1.4 × 106, 2.3 × 106, and 3.5 × 105 s–1 for lanthanum, zinc, and terbium cations, respectively.

Photonics of 18-crown-6-containing styryl dye and its complexes with metal cations

Using absorption, luminescence, 1H NMR, and laser kinetic spectroscopies, the photophysical processes and photochemical reactions of 4-[(E)-2-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)vinyl]-1-ethylpyridinium perchlorate and its complexes with lithium, sodium, potassium, calcium, barium, silver, and lead perchlorates in MeCN have been studied. The styryl dye and its complexes with metal cations are capable of emitting normal (prompt) and delayed fluorescence and enter into the trans–cis photoisomerization reaction. The dye molecules in the triplet state participate in the processes of degradation of electronic excitation energy. Triplet–triplet absorption is observed only in the presence of lead cations with a maximum at 470 nm and the deactivation rate constant of the triplet state k = 2.5 × 104 s–1 in a deoxygenated solution.

Photoprocesses in N-ammonioalkyl derivatives of azacrown-containing styryl dyes and their complexes with metal perchlorates

Photophysical processes and photochemical reactions in the N-ammonioalkyl derivatives of the azacrown-containing styryl dyes and their complexes with lead and barium perchlorates in MeCN and CH2Cl2 were studied by 1Н NMR spectroscopy, absorption spectroscopy, luminescence spectroscopy, laser kinetic spectroscopy, and quantum chemistry. Molecules of the styryl dyes and their complexes are able to undergo normal (fast) and delayed fluorescence and trans–cis-photoisomerization. The molecules in the triplet state participate in degradation processes of the electron excitation energy.

Photonics of N-ammonioalkyl derivatives of azacrown-containing styryl dyes

Photophysical and photochemical processes in diperchlorates of styryl dyes containing an N-ammonioalkyl substituent have been studied by the absorption, luminescence, and laser kinetic spectroscopy techniques. Participation of the triplet state in photoexcitation energy degradation processes and the ability of the dyes to enter the trans-cis photoisomerization reaction have been revealed. Dimerization and delayed fluorescence of the dyes at 77 K have been detected.

Effect of medium dielectric properties on spontaneous emission of molecular singlet oxygen

Radiative rate constants (k r ) were determined using laser kinetic spectroscopy of singlet oxygen O2 (a 1 Δg) luminescence in solutions with regularly changed refractive indices. It was shown that changes in the radiative rate constants were caused by both the inherent properties of the emitting O2 molecule and the characteristics of the ambient medium that defined the local field factor and the density of the field finite states.

Photonics of azacrown-containing styryl dye and its complexes with metal ions: 1. Triplet states

Photophysical processes in a styryl dye; an azacrown-containing analog; and its complexes with barium, lead, calcium, sodium, and silver cations have been studied by laser kinetic and luminescent spectroscopy. The participation of the triplet state in the degradation of photoexcitation energy has been established. Phosphorescence and delayed fluorescence of dyes and its complexes have been revealed found. It has been concluded that the molecules can exist in the excited TICT state.

The kinetics of molecular oxygen migration in the isolated α chains of human hemoglobin as revealed by molecular dynamics simulations and laser kinetic spectroscopy

Bimolecular and geminate molecular oxygen (O 2) rebinding to isolated α chains of human adult hemoglobin in solutions is analyzed. Multiple extended molecular dynamics (MD) simulations of the O 2 migration within the protein after dissociation are described. Computational modeling is exploited to identify hydrophobic pockets within the α chains and internal O 2 migration pathways associated with the experimentally observed ligand rebinding kinetics. To initiate dissociation, trajectories of the liganded protein are interrupted, the iron–dioxygen bond is broken, and the parameters of the iron–nitrogen bonds are simultaneously altered to produce a deoxyheme conformation. MD simulations provide 140 essentially independent trajectories (up to 25-ns long) of the O 2 migration in the protein. The time dependence of cavities occupancy, obtained by the MD simulations, and the kinetics of O 2 rebinding, measured by flash-photolysis techniques, allow us to obtain the kinetics of the entire O 2 migration process within the nanosecond time range and construct an explicit kinetic model of the O 2 migration and rebinding process. The amino acids that have the most pronounced effect on the ligand migration within the α chain matrix are predicted.