Jerzy Karolczak

A pyrolysis jet spectroscopic study of the rotationally resolved electronic spectrum of dichlorocarbene

The rotationally resolved, gas phase vibronic spectrum of dichlorocarbene has been recorded using the technique of pyrolysis jet spectroscopy. The rovibronic analysis has established the band origin of the A 1B1–X 1A1 electronic transition to be at 17 255.67 cm−1. The observed vibrational frequencies in the ground and excited states are very close to published values from matrix isolation data. The excited state structure has a 131.4° ClCCl angle and a 1.652 A CCl bond length.

The measurements of picosecond fluorescence lifetimes with high accuracy and subpicosecond precision

Abstract Systematic studies of the fluorescence picosecond lifetimes determination by laser-excited time-correlated single-photon-counting (TCSPC) have been undertaken. The results have been used to develop methods for determining lifetimes with much smaller error and much greater reproducibility than any hitherto reported. The error in the determination of the lifetimes (±three standard deviations) can be as low as that in simulations and amounts to 0.01 FWHM of the IRF. The lifetimes determined for the second excited singlet state of xanthione in toluene (5.1±0.3 ps ) and in benzene (8.1±0.3 ps ) can be treated as reliable standards of picosecond lifetimes.

Photophysical properties of tyrosine at low pH range

Abstract The global analysis of the fluorescence intensity decays of tyrosine across the emission spectrum at pH=0 revealed that its fluorescence intensity decay is bi-exponential with fluorescence lifetimes equal to 63±7 ps and 1.030±0.009 ns, whereas, the global analysis of the fluorescence intensity decays of tyrosine at different pH revealed that the quenching of tyrosine fluorescence by H 3 O + ions is connected with the presence of protonated carboxyl group. The lack of acid–base equilibrium in the excited state or disturbance of this equilibrium by an additional quenching process caused the discrepancy between experimental points and Hendersson–Haselbalch relationship.

Comparison of TiO2 and ZnO Solar Cells Sensitized with an Indoline Dye: Time-Resolved Laser Spectroscopy Studies of Partial Charge Separation Processes

Time-resolved laser spectroscopy techniques in the time range from femtoseconds to seconds were applied to investigate the charge separation processes in complete dye-sensitized solar cells (DSC) made with iodide/iodine liquid electrolyte and indoline dye D149 interacting with TiO2 or ZnO nanoparticles. The aim of the studies was to explain the differences in the photocurrents of the cells (3-4 times higher for TiO2 than for ZnO ones). Electrochemical impedance spectroscopy and nanosecond flash photolysis studies revealed that the better performance of TiO2 samples is not due to the charge collection and dye regeneration processes. Femtosecond transient absorption results indicated that after first 100 ps the number of photoinduced electrons in the semiconductor is 3 times higher for TiO2 than for ZnO solar cells. Picosecond emission studies showed that the lifetime of the D149 excited state is about 3 times longer for ZnO than for TiO2 samples. Therefore, the results indicate that lower performance of ZnO solar cells is likely due to slower electron injection. The studies show how to correlate the laser spectroscopy methodology with global parameters of the solar cells and should help in better understanding of the behavior of alternative materials for porous electrodes for DSC and related devices.

Measurements of picosecond lifetimes by time correlated single photon counting method: The effect of the refraction index of the solvent on the instrument response function

The article concerns the possibility of precise picosecond lifetime measurements by the method of the time correlated single photon counting (TCSPC). The lifetimes (τ) of S2 fluorescence of xanthione measured in different solvents have shown that it is possible to obtain τ as short as a few picoseconds. The values of τ varying from ∼5 to ∼38 ps in solvents whose refraction indices range from 1.34 to 1.50 have been proposed as picosecond standards in lifetime measurements. However, in order to obtain reliable results some conditions must be met: the effect of the absorbing and emitting impurities must be eliminated, the instrument response function (IRF) must be very stable and correctly determined, and because of a much lower time resolution of the TCSPC method relative to that of the upconversion method, the procedure of measurements and numerical analysis of results proposed in our work should be applied. In the study reported the effect of impurities was eliminated by applying high performance liquid c...

Synthesis and photophysical properties of 3-[2-(pyridyl)benzoxazol-5-yl]-l-alanine derivatives

Abstract The syntheses of N -( tert -butyloxycarbonyl)-3-[2-(4-pyridyl)benzoxazol-5-yl]- l -alanine methyl ester and N -( tert -butyloxycarbonyl)-3-[2-(2-pyridyl)benzoxazol-5-yl]- l -alanine methyl ester using different oxidizing agents (NBS, lead tetraacetate, Mitsunobu reaction) in oxidative cyclization of Schiff base are described. The compounds obtained are fluorescent. The position of the emission band and the fluorescence quantum yield depend on solvent polarity. The fluorescence decays of all the compounds studied are heterogeneous.

Mechanism of fluorescence quenching of tyrosine derivatives by amide group

Abstract The difference between fluorescence lifetimes of the following amino acids: phenylalanine (Phe), tyrosine (Tyr), ( O -methyl)tyrosine (Tyr(Me)), (3-hydroxy)tyrosine (Dopa), (3,4-dimethoxy)phenylalanine (Dopa(Me) 2 ) and their amides was used to testify the mechanism of fluorescence quenching of aromatic amino acids by the amide group. On the basis of the Marcus theory of photoinduced electron transfer parabolic relationships between ln k ET and ionization potentials reduced by energy of excitation ( IP −E ∗ 0,0 ) for the above-mentioned amino acids were obtained. This finding indicates the occurrence of photoinduced electron transfer from the excited chromophore group to the amide group.

Acid–Base Equilibriums of Lumichrome and its 1-Methyl, 3-Methyl, and 1,3-Dimethyl Derivatives

Lumichrome photophysical properties at different pH were characterized by UV-vis spectroscopy and steady-state and time-resolved fluorescence techniques, in four forms of protonation/deprotonation: neutral form, two monoanions, and dianion. The excited-state lifetimes of these forms of lumichrome were measured and discussed. The results were compared to those obtained for similar forms of alloxazine and/or isoalloxazine, and also to those of 1-methyl- and 3-methyllumichrome and 1,3-dimethyllumichrome. The absorption, emission, and synchronous spectra of lumichrome, 1-methyl- and 3-methyllumichrome, and 1,3-dimethyllumichrome at different pH were measured and used in discussion of fluorescence of neutral and deprotonated forms of lumichrome. The analysis of steady-state and time-resolved spectra and the DFT calculations both predict that the N(1) monoanion and the N(1,3) dianion of lumichrome have predominantly isoalloxazinic structures. Additionally, we confirmed that neutral lumichrome exists in its alloxazinic form only, in both the ground and the excited state. We also confirmed the existence and the alloxazinic structure of a second N(3) monoanion. The estimated values of pK(a) = 8.2 are for the equilibrium between neutral lumichrome and alloxazinic and isoalloxazinic monoanions, with proton dissociation from N(1)-H and N(3)-H groups proceeding at the almost the same pH, while the second value pK(a) = 11.4 refers to the formation of the isoalloxazinic dianion in the ground state.

Mechanism and deactivation kinetics of S2-xanthione in acetonitrile, a quenching solvent, and of S2-exciplex measured by pico- and femtosecond laser spectroscopy

Abstract The Letter discusses the mechanism and dynamics of intra- and intermolecular electronic relaxation of the S 2 state of a xanthione molecule in acetonitrile, a quenching solvent, as well as the most important properties of the S 2 -exciplex formed upon the quenching process. Despite very efficient quenching of S 2 -XT and other thiones it has not been possible so far to observe the S 2 -exciplex. Therefore transient absorption system with 120 fs resolution was successfully applied for this purpose: the S 2 -exciplex was identified for the first time, its lifetime (∼30 ps) and transient absorption spectrum were determined as well as the mechanism of its formation and decay. Moreover, the authors observed the presence of a very fast intramolecular electronic relaxation process (S 2 v >0 →S 0 ) during S 2 -state deactivation which competes with intramolecular vibrational redistribution in the S 2 -state.

Determination of ferrocene triplet lifetime by measuring T1→T1 energy transfer to phenylosazone-D-glucose

Abstract The lifetime of ferrocene in the triplet state T1, τT1 = 0.6 ns, was determined in dimethyl sulfoxide at room temperature by ferrocene-sensitized photoisomerization of phenylosazone-D-glucose. Using laser flash photolysis it was found that for ferrocene within the spectral range 300–700 nm, the value of the molar absorption coefficient for T1→Tn transitions is lower than 500 M−1 cm−1.