Search

The way the spin state of an acceptor influences the photophysical processes in a donor-bridge-acceptor (D-B-A) system is investigated. The dominating photophysical process is drastically changed by switching the acceptor to a low-spin state where the low spin system shows long-range electron transfer on the picosecond time scale and intersystem crossing occurs as its 'normal rate', as per demonstration.

The studies were conducted to investigate the triplet excited-state deactivation of a gold porphyrin (AuP) in porphyrin-based donar-bridge-acceptor (D-B-A) systems. The results show that quenching of (super 3) AuP occurs with high efficiency in the dimers that were connected by fully conjugated budging chromophores, whereas no quenching was observed when the conjugation of the bridge was broken.

The investigation and synthesization of a series of new Ru(II) complexes containing the carboxylatopyridine ligand moiety were conducted using single-crystal X-ray diffraction, nuclear magnetic resonance, electrospray mass spectrometry, cyclic voltammetry, absorption and emission spectroscopy. Results reveal a general correlation of the electrochemical properties and the number of carboxylate groups per complex.

Binuclear ruthenium-manganese complexes were tested to provide a series of artificial models for photosystem II (PSII) in green plants. Ruthenium(II) tris(bipyridyl) complex was then covalently linked to a manganese(II) ion by two varying bridging ligands, mimicking the function of P(sub) 680 in the electron transfer cited in PSII. Results showed the importance of coordinated manganese ion in restoring the activity of photo-oxidized photosensitizer through intramolecular electron transfer.

The trapping and conversion of visible light energy into chemical energy is examined by using a supramolecular assembly. The results have shown the suitability of the system as a prototype for DNA-based light-harvesting devices, in which energy transfer from the aqueous phase to the interior of the lipid membrane is followed by charge separation.

A series of donor-bridge-acceptor (D-B-A) systems with varying donor-acceptor distances was analyzed with respect to their energy transfer properties. The study was performed in 2-MTHF at 150K and it was found that triplet excitation energy transfer occurs with high efficiency in all D-B-A systems with the distance dependence being exponential and the donor and acceptor chromophores were separated by oligo-p-phenyleneethynylene (OPE) bridge units.

A plausible rate-determining step and its transition-state structure for the Heck alkynylation (copper-free Sonogashira) reaction are described. The very high yielding and successful synthesis of a series of porphyrin systems using these new conditions is presented and for the first time, gold porphyrin substrates could efficiently be coupled in Heck alkynylation reactions.

The electron transfer process in the ZnP-nB-AuP(super +) systems is verified by detection of formation and decay of the zinc porphyrin radical cation with femtosecond transient absorption spectroscopy. The efficiency of electron transfer, based on time-resolved fluorescence measurements, is 0.98, 0.77, 0.31, and 0.14 in C3H7CN for ZnP-nB-AuP(super +) with the edge to edge distance 12.7, 19.6, 26.5, an d33.4 Angstrom, respectively.

The donor-acceptor distance and donor-bridge energy dependence of singlet energy transfer in a series of D-B-A systems are studied. Both experimental and theoretical methods are used, and a consistent description of the energy-transfer process emerges from the study.

An investigation of the photophysics of gold(III) porphyrins with steady state and time-resolved spectroscopic methods as well as DFT calculations is presented. The result suggests a short-lived state, with a lifetime of about 20-50 ns in rigid media that is an intermediate between the first excited singlet state and the triplet manifold and acts as a gatekeeper state for formation of the triplets.

A Mn(III,III) dinuclear complex with phenolate ligands is oxidized to Mn(III,IV) by photogenerated Ru(III) with a rate constant. The preparation of donor (D)-photosensitizer (S) arrays, consisting of a manganese complex as D and a ruthenium tris(bipyridal) complex as S is tracked.

The excited triplet state conformations of zinc and free base 5,15-diaryloctaalkylporhyrins are studied by experimental and computational methods. X-ray crystallography and DFT (B3LYP/6-31G(d)) optimization of the ground state show that the porhyrins are planar prior to excitation.

The exited triplet state deactivation of zinc(II) meso-diaryloctaalkylporphyins (ZnDAOAP) has been studied over a wide temperature range using triplet- triplet absorption spectroscopy together with steady-state and time-resolved phosphorescence techniques. The triplet species have a 'mother -daughter' relationship and the ground state recovery at room temperature is governed exclusively by a route via the daughter state, as the direct intersystem crossing from the mother state is slow.

Singlet electronic energy transfer (EET) in two donor-bridge-acceptor series in which the donor and the acceptor were covalently connected by a geometrically well-defined bridging chromophore was studied. How the medium between a donor and an acceptor influences EET by separating the influence of the electronic structure of the bridging chromophore from other effects known to influence the energy transfer was investigated. The results showed that the bridging chromophore did not significantly enhance the energy rate constant.

Examines bridge-dependent electron transfer in porphyrin-based donor-bridge-acceptor systems. Synthesis; Ground-state absorption; Emission properties; Donor intersystem crossing; Energy transfer; Electrochemistry; Electron transfer; Transient absorption.