H.J. van Ramesdonk

Measurement and global analysis of the absorbance changes in the photocycle of the photoactive yellow protein from Ectothiorhodospira halophila.

The photocycle of the photoactive yellow protein (PYP) from Ectothiorhodospira halophila was examined by time-resolved difference absorption spectroscopy in the wavelength range of 300-600 nm. Both time-gated spectra and single wavelength traces were measured. Global analysis of the data established that in the time domain between 5 ns and 2 s only two intermediates are involved in the room temperature photocycle of PYP, as has been proposed before (Meyer T.E., E. Yakali, M. A. Cusanovich, and G. Tollin. 1987. Biochemistry. 26:418-423; Meyer, T. E., G. Tollin, T. P. Causgrove, P. Cheng, and R. E. Blankenship. 1991. Biophys. J. 59:988-991). The first, red-shifted intermediate decays biexponentially (60% with tau = 0.25 ms and 40% with tau = 1.2 ms) to a blue-shifted intermediate. The last step of the photocycle is the biexponential (93% with tau = 0.15 s and 7% with tau = 2.0 s) recovery to the ground state of the protein. Reconstruction of the absolute spectra of these photointermediates yielded absorbance maxima of about 465 and 355 nm for the red- and blue-shifted intermediate with an epsilon max at about 50% and 40% relative to the epsilon max of the ground state. The quantitative analysis of the photocycle in PYP described here paves the way to a detailed biophysical analysis of the processes occurring in this photoreceptor molecule.

Luminescent materials and devices: lanthanide azatriphenylene complexes and electroluminescent charge transfer systems

Abstract It is shown that the successful sensitization of lanthanide luminescence by azatriphenylenes can be expanded from sensitization in non-hydroxylic solvents to aqueous media by the addition of two or more carboxylate functionalities on the triphenylene skeleton. Furthermore, it is reported that a fluorescent donor–bridge–acceptor system incorporated in a thin polymer film allows the production of blue electroluminescence that can be tuned from blue to yellow by exposure to solvent vapours.

Intramolecular charge-transfer fluorescence as a mobility probe in poly(methylmethacrylate)

Abstract The (time-resolved) fluorescence spectra of 1-phenyl-4-(4-cyano-1-naphthylmethylene)piperidine (1) have been measured during the polymerization of methylmethacrylate (MMA). It was found that the fluorescence maximum of 1 shows a large hypsochromic shift as polymerization of the MMA medium progresses. While the emission maximum is located at 565 nm in the monomer, it is found at 450 ± 5 nm in the polymer (PMMA). The polarization of the fluorescence increases strongly during the polymerization, indicating that the rotational motion of 1 ceases on the timescale of the fluorescence lifetime (about 10 ns). Fluorescence measurements performed with a detection time delay with respect to the exciting laser pulse showed that within the time range 0–100 ns the molecule 1 undergoes reorientation and/or internal relaxation even in a PMMA matrix; a red shift of the emission with time occurs, together with a decrease of the degree of fluorescence polarization.

Electrostatically driven folding following light-induced intramolecular electron transfer in a trichromophoric electron donor—acceptor molecule

Abstract Time-resolved fluorescence and microwave conductivity data indicate that the trichromophoric donor 2 —bridge—donor 1 —acceptor compound 1 undergoes a large conformational change leading to a sandwich-like exciplex following light-induced long-range electron transfer in alkane solvents.

Pyridine-dinucleotide models IV; stereoselective hydride transfer at a bridged pyridinium-ion

Abstract Two achiral bridged 1,4-dihydro-3,5-biscarboxamido pyridines are described. In one of these the bridging induces significant diastereotopy of the C-4 protons. This not only leads to magnetic anisochrony of these protons, but also allows for highly stereoselective (- 90%) substitution of one of them by deuterium via hydride exchange with a simple deuterated dihydropyridine.

Charge separation in the excited state of electron donor-acceptor compounds containing the piperazine moiety

Three bridged electron donor—acceptor systems are investigated containing a 4-cyano-1-ethenylnaphthalene electron-acceptor and piperidine (compound 1), phenylpiperazine (2) and 4-methoxyphenylpiperazine (3) electron-donating groups. In the intramolecular charge-transfer states of 1 and 2, the extent of charge separation is similar, but in compound 3 the positive charge is shifted towards the more powerful arylamine donor site, which results in a significantly greater dipole moment. Optical absorption spectra of model radical cations demonstrate that the predominant charge localization on the trialkyl nitrogen in 2 and on the aryl nitrogen in 3 are a consequence of the bistable nature of the piperazine donors.

Enhanced intersystem crossing in 3-(1-pyrenyl)propylbromide

Abstract Using opto-acoustic spectroscopy, transient absorption spectroscopy and time-resolved fluorescence spectroscopy, it could be demonstrated that the rate constant for intersystem crossing of 3-(1-pyrenyl)-propylbromide is twice that the model compound 1-methylpyrene. The effect of the intramolecular interaction between bromine and pyrene on the rate constant of intersystem crossing leads to a value that is still several orders of magnitude smaller than the rate constant for the intramolecular excimer formation of 1,3-di(2-pyrenyl)-propane or of intramolecular exciplex formation in 1-N,N-dimethylamino-3-(1-pyrenyl)-propane. This suggests that the contribution of the interaction between bromine and pyrene to the rate constant for intersystem crossing is considerably below the values expected for a process whose rate is limited by the rate of folding of the propyl chain.

Intramolecular Charge Transfer Fluorescence of 1-Phenyl-4-(4-Cyano-1-Naphthylmethylene)Piperidine as a Mobility Probe in α,ω-Diacetyl Poly(Ethyleneglycols)

Continuous- and time-resolved fluorescence measurements of l-phenyl-4-(4-cyano-l-naphthyl-methylene)piperidine (Fluoroprobe) dissolved in α,ω-diacetyl poly(ethyleneglycols) show that fluorescence occurs prior to full relaxation of the surrounding matrix sites.