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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.

An optimized one‐pot recipe has been developed to synthesize a surfactant molecule, referred to as OMID, consisting of an imidazoline head group and aliphatic tail, which is an exemplar corrosion inhibitor for carbon steel in acidic solutions. As evidenced by gas chromatography, 1H and 13C nuclear magnetic resonance, and Fourier‐transform infrared data, a high‐purity product was achieved without the use of either a solvent or catalyst. Critical micelle concentration values and corrosion inhibition efficiencies (η%) were determined in aqueous solutions of hydrochloric acid and sulfuric acid using surface tensiometry and linear polarization resistance measurements, respectively. Hydrolysis of the imidazoline head group as a function of pH (0–11) was explored with ultraviolet–visible absorption spectroscopy. In addition, N 1s and C 1s X‐ray photoelectron spectroscopy data were acquired from both surface‐adsorbed OMID and a multilayer of the imidazoline head group of OMID. These latter data are highly relevant to those attempting to understand OMID inhibition chemistry. [ABSTRACT FROM AUTHOR]

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.

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.

In this paper, our attempts to optimize the Heck alkynylation (copper-free Sonogashira) reaction are presented. An efficient copper-free coupling protocol was needed for the synthesis of gold/zinc porphyrin dimers because previous methods had failed. Previous studies have usually focused on ligands, whereas this work focuses on the choice of solvent and base. The catalytic system throughout the investigation was formed from the stable precursor [Pd2(dba)3·CHCl3] together with the ligand triphenylarsine, an easy-to-handle, air-stable ligand. A model study was conducted to examine the dependence of the Heck alkynylation on the solvent and base. The most successful modification proved to be the addition of methanol, as a cosolvent, in combination with a nucleophilic tertiary base. The success of the methanol additive is hypothesized to be caused by the presence of a rate-determining deprotonation step featuring a charge-separated transition state. Finally, the very high yielding and successful synthesis of a series of porphyrin systems using these new conditions is presented. For the first time, gold porphyrin substrates could efficiently be coupled in Heck alkynylation reactions. [ABSTRACT FROM AUTHOR]

Optimizing the ratio of the rates for charge separation (CS) over charge recombination (CR) is crucial to create long-lived charge-separated states. Mastering the factors that govern the electron transfer (ET) rates is essential when trying to achieve molecular-scale electronics, artificial photosynthesis, and also for the further development of solar cells. Much work has been put into the question of how the donor-acceptor distances and donor-bridge energy gaps affect the electronic coupling, VDA, and thus the rates of ET. We present here a unique comparison on how these factors differently influence the rates for CS and CR in a porphyrin-based donor-bridge-acceptor model system. Our system contains three series, each of which focuses on a separate charge-transfer rate-determining factor, the donor-acceptor distance, the donor-bridge energy gap, and last, the influence of the electron acceptor on the rate for charge transfer. In these three series both CS and CR are governed by superexchange interactions which make a CR/CS comparative study ideal. We show here that the exponential distance dependence increases slightly for CR compared to that for CS as a result of the increased tunneling barrier height for this reaction, in accordance with the McConnell superexchange model. We also show that the dependence on the tunneling barrier height is different for CS and CR. This difference is highly dependent on the electron acceptor and thus cannot solely be explained by the differences in the frontier orbitals of the electron donor in these porphyrin systems. [ABSTRACT FROM AUTHOR]

Singlet excitation energy transfer is governed by two donor-acceptor interactions, the Coulombic and exchange interactions giving rise to the Förster and Dexter mechanisms, respectively, for singlet energy transfer. In transfer between colliding molecules or between a donor (D) and acceptor (A) connected in donor-bridge-acceptor (D-B-A) system by an inert spacer (B), the distinction between these two mechanisms is quite clear. However, in D-B-A systems connected by a pi-conjugated bridge, the exchange interaction between the donor and acceptor is mediated by the virtual low-lying excited states (unoccupied orbitals) of that bridge and, as a consequence, becomes much more long-range in character. Thus, the clear distinction to the Coulombic mechanism is lost. This so-called superexchange mechanism for singlet energy transfer has been shown to make a significant contribution to the energy transfer rates in several D-B-A systems, and its D-A distance as well as D-B energy gap dependencies have been studied. We here demonstrate that in a series of oligo-p-phenyleneethynylene (OPE) bridged porphyrin-based D-B-A systems with varying D-A distances the Förster and through-bond (superexchange) mechanisms both make considerable contributions to the observed singlet energy transfer rates. The donor is either a zinc porphyrin or a zinc porphyrin with a pyridine ligand, and the acceptor is a free base porphyrin. By comparison to a homologous series where only the D-B energy gaps varies, a separation between the two energy transfer mechanisms was possible and, moreover, an interplay between distance and energy gap dependencies was noted. The distance dependence was shown to be approximately exponential with an attenuation factor beta=0.20 A-1. If the effect of the varying D-B energy gaps in the OPE series was taken into account, a slightly higher beta-value was obtained. Ground-state absorption, steady-state, and time-resolved emission spectroscopy were used. The experimental study is accompanied by time-dependent density functional theory (TD-DFT) calculations of the electronic coupling, and the experimental and theoretical results are in excellent qualitative agreement (same distance dependence).