Pathways of electron transfer photosensitized by thiacyanine dimers.

Pathways of electron transfer reaction between p-nitroacetophenone (p-NAP) and ascorbic acid (AA) photosensitized by dimers of 3,3'-disulfopropyl-5,5'-dichlorothiacyanine triethylammonium (TC) and 3,3'-disulfopropyl-5,5'-dichloro-9,11-[ββ-dimethyltrimethylene]thiadicarbocyanine triethylammonium (TDC) are considered. In aqueous solution the dyes are present as an equilibrated mixture of monomers (M(-)) and dimers (M(2)(2-)). In contrast to monomers, the dimers of TC are characterized by a noticeable yield of intersystem crossing, whereas for TDC the triplet-triplet absorption of both monomers and dimers is easily observed upon ns-laser pulse.

Cyanine-based J-aggregates as a chirality-sensing supramolecular system.

J-aggregates are formed for 3,3'-disulfopropyl-5,5'-dichlorothiacyanine (Tc) and 3,3'-disulfobutyl-5,5'-diphenyl-9-ethyloxacarbocyanine (Oc) in aqueous solution in the presence of NaCl, Mg(NO(3))(2), d/l-tartaric acids, asparagine, proline, DNA, and proteins, such as lysozyme, trypsin, RNase, and gelatin. J-aggregates, which are formed in the presence of chiral additives, are optically active and characterized by sigmoidal kinetics with half-times of 10-1000 s, resonance fluorescence, and large CD amplitudes being up to 2° for Tc. Generally, the induced CD signals of the J-aggregates of both dyes are bisignate and the sign corresponds to that of the additive.

J-aggregation of anionic ethyl meso-thiacarbocyanine dyes induced by binding to proteins.

The effects of ribonuclease A (RNase), lysozyme, trypsin, and bovine serum albumin (BSA) on the J-aggregation behavior of 3,3'-bis[sulfopropyl]-5-methoxy-4',5'-benzo-9-ethylthiacarbocyanine (1), 3,3'-bis[sulfopropyl]-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine (2), and 3,3'-bis[sulfopropyl]-5,5'-dimethoxy-9-ethylthiacarbocyanine (3) were studied in aqueous solution. The formation of J-aggregates at pH 6 is induced by RNase for 1-3, by lysozyme for 1 and 2, and by trypsin for 2. The formation of J-aggregates correlates with decay of the dimers and is supported by induced circular dichroism spectra.

Wavelength-tunable ultrashort-pulse output of a photonic-crystal fiber designed to resolve ultrafast molecular dynamics.

Wavelength-tunable 100 fs pulses generated through the soliton self-frequency shift in a photonic-crystal fiber are employed to visualize femtosecond coherence and population relaxation dynamics in molecular aggregates by means of time-resolved sum-frequency generation. This technique reveals an ultrafast dephasing of coherent molecular excitations with a phase relaxation time of about 120 fs and resolves an ultrafast switching of the nonlinear-optical response of molecular aggregates.

Frequency-shifted megawatt soliton output of a hollow photonic-crystal fiber for time-resolved coherent anti-Stokes Raman scattering microspectroscopy.

Hollow-core photonic-crystal fibers (PCFs) provide soliton delivery and frequency shifting of 2.8 MW femtosecond pulses with an input central wavelength of 618 nm. The frequency-shifted megawatt soliton output of the hollow PCF is used as a high-peak-power Stokes field for coherent anti-Stokes Raman scattering (CARS) microspectroscopy, providing a dynamic range of nearly four decades for anti-Stokes signal detection, thus enabling time-resolved CARS studies of ultrafast relaxation processes on time scales from tens of femtoseconds up to tens of picoseconds.

Kinetics of salt-induced J-aggregation of cyanine dyes.

The addition of monovalent, divalent, and trivalent metal ions to three anionic ethyl meso-thiacarbocyanine dyes, an ethyl meso-oxacarbocyanine, and an imidacarbocyanine in aqueous solution at room temperature results in the production of J-aggregates within the range of tens to hundreds of seconds. The rate of formation of J-aggregates correlates with the rate of decay of dimers or monomers and is dependent on the type of metal ion, dye structure, and temperature. The rate of formation of J-aggregates increases as the temperature decreases and the dye and salt concentrations increase, and the rate is highest for trivalent ions and smallest for monovalent ions, independent of the type of anion.