Solvent dependent photosensitized singlet oxygen production from an Ir(III) complex: pointing to problems in studies of singlet-oxygen-mediated cell death.

A cationic cyclometallated Ir(III) complex with 1,10-phenanthroline and 2-phenylpyridine ligands photosensitizes the production of singlet oxygen, O2(a(1)Δ(g)), with yields that depend appreciably on the solvent. In water, the quantum yield of photosensitized O2(a(1)Δ(g)) production is small (ϕ(Δ) = 0.036 ± 0.

Experimental and computational study of solvent effects on one- and two-photon absorption spectra of chlorinated harmines.

A combined experimental and computational study of solvent effects on one- and two-photon absorption spectra of three chlorinated harmine derivatives is presented. The systems studied were protonated forms of 6-chloroharmine, 8-chloroharmine and 6,8-dichloroharmine in two solvents, acetonitrile and water. For the computations, polarizable embedding density functional and coupled cluster response theory methods were used.

Rational design of an efficient, genetically encodable, protein-encased singlet oxygen photosensitizer.

Singlet oxygen, O(2)(a(1)Δ(g)), plays a key role in many processes of cell signaling. Limitations in mechanistic studies of such processes are generally associated with the difficulty of controlling the amount and location of O(2)(a(1)Δ(g)) production in or on a cell. As such, there is great need for a system that (a) selectively produces O(2)(a(1)Δ(g)) in appreciable and accurately quantifiable yields and (b) can be localized in a specific place at the suborganelle level.

Imaging molecular structure through femtosecond photoelectron diffraction on aligned and oriented gas-phase molecules.

This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray free-electron laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C(8)H(5)F) and dissociating, laser-aligned 1,4-dibromobenzene (C(6)H(4)Br(2)) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.

Effect of chromophore encapsulation on linear and nonlinear optical properties: the case of "miniSOG", a protein-encased flavin.

Linear and nonlinear spectroscopic parameters of flavin mononucleotide, FMN, have been examined both experimentally and computationally under conditions in which FMN is (1) solvated in a buffered aqueous solution, and (2) encased in a protein that is likewise solvated in a buffered aqueous solution. The latter was achieved using "miniSOG" which is an FMN-containing protein engineered from Arabidopsis thaliana phototropin 2. Although it is reasonable to expect that the encasing protein could have an appreciable effect, certainly on the nonlinear two-photon absorption cross section, we find that replacing the dynamic aqueous environment with the more static protein environment does little to influence the spectroscopic properties of FMN.

Temperature effect on radiative lifetimes: the case of singlet oxygen in liquid solvents.

A change in solvent can have an appreciable effect on the rate constant for the O2(a(1)Δg) → O2(X(3)Σg(-)) radiative transition at ~1275 nm. The data thus obtained have played an important role in understanding mechanisms by which environment-dependent perturbations can influence forbidden electronic transitions. We now report that the rate constant for O2(a(1)Δg) radiative deactivation, kr, also responds to changes in temperature.

Singlet-oxygen-mediated cell death using spatially-localized two-photon excitation of an extracellular sensitizer.

Controlling and quantifying the photosensitized production of singlet oxygen are key aspects in mechanistic studies of oxygen-dependent photoinitiated cell death. In this regard, the commonly accepted practice of using intracellular photosensitizers is, unfortunately, plagued by problems that include the inability to accurately (1) quantify the sensitizer concentration in the irradiated domain and (2) control the local environment that influences light delivery and sensitizer photophysics. However, capitalizing on the fact that singlet oxygen produced outside a cell is also cytotoxic, many of these problems can be avoided with the use of an extracellular sensitizer.

Laser-induced 3D alignment and orientation of quantum state-selected molecules.

A strong inhomogeneous static electric field is used to spatially disperse a rotationally cold supersonic beam of 2,6-difluoroiodobenzene molecules according to their rotational quantum state. The molecules in the lowest-lying rotational states are selected and used as targets for 3-dimensional alignment and orientation. The alignment is induced in the adiabatic regime with an elliptically polarized, intense laser pulse and the orientation is induced by the combined action of the laser pulse and a weak static electric field.

Quantum-state selection, alignment, and orientation of large molecules using static electric and laser fields.

Supersonic beams of polar molecules are deflected using inhomogeneous electric fields. The quantum-state selectivity of the deflection is used to spatially separate molecules according to their quantum state. A detailed analysis of the deflection and the obtained quantum-state selection is presented.

Laser-induced alignment and orientation of quantum-state-selected large molecules.

A strong inhomogeneous static electric field is used to spatially disperse a supersonic beam of polar molecules, according to their quantum state. We show that the molecules residing in the lowest-lying rotational states can be selected and used as targets for further experiments. As an illustration, we demonstrate an unprecedented degree of laser-induced one-dimensional alignment (cos;(2)theta_(2D)=0.

Multiphoton electron angular distributions from laser-aligned CS2 molecules.

Laser-aligned carbondisulfide (CS2) molecules are singly ionized by multiphoton absorption from intense, linearly polarized 25 fs laser pulses. The angular distribution of the photoelectrons exhibits a significant dependence on the angle between the polarizations of the aligning and ionizing laser fields. The widely used strong-field approximation predicts angular distributions in qualitative agreement with the experimental data but fails at a quantitative level.

Role of rotational temperature in adiabatic molecular alignment.

One-dimensional alignment of molecules in the adiabatic limit, where the pulse duration greatly exceeds the molecular rotational periods, is studied experimentally. Four different asymmetric top molecules (iodobenzene, p-diiodobenzene, 3,4-dibromothiophene, and 4,4'-dibromobiphenyl), rotationally cooled through a high pressure supersonic pulsed valve, are aligned by a 9-ns-long pulse. Their orientations are measured through Coulomb explosion, induced by a 130-fs-long pulse, and by recording the direction of the recoiling ions.