Control Of Electron Transfer Processes Research Articles

Control of Electron Transfer Processes in Multidimensional Arylamine-Based Mixed-Valence Compounds by Molecular Backbone Design.

Four trigonal topology compounds with three diarylamines redox centers and dibenzofulvene as core bridge have been synthesized. Their radical cations exhibit appealing intramolecular electron transfer pathways between three redox centers, depending on their position on the core bridge. By changing such positions (on either 2,7- or 3,6-), and the length of the bridge, the control of the intramolecular electron transfer pathways was achieved through the electron self-exchange route. These processes were investigated by absorption spectroscopy, electron paramagnetic resonance spectroscopy, and (time-dependent) density functional theory calculations. Hole mobility measurements were carried out as well, to correlate the intramolecular electron transfer with the hole-transporting ability for possible applications in optoelectronic devices.

Long-lived charge-separated states of simple electron donor-acceptor dyads using porphyrins and phthalocyanines

Control of electron-transfer processes is described for a number of electron donor-acceptor dyads containing porphyrins or phthalocyanines as models for the photosynthetic reaction center. The rates for intramolecular electron transfer in the dyads are controlled by the driving force and reorganization energy of electron transfer. The small reorganization energy of electron transfer reactions and large driving force of charge recombination are required to form long-lived charge-separated states. A directly linked zinc chlorin-fullerene dyad, especially, has the longest lifetime of charge-separated state at 120 s at -150 °C, which is a much longer lifetime and higher energy than those of natural photosynthetic reaction centers. On the other hand, the charge-separated states of the phthalocyanine-based donor-acceptor dyads (silicon phthalocyanine-fullerene, and zinc phthalocyanine-perylenebisimide) are short-lived since charge recombination forms the low-lying triplet excited state of the chromophore. The energy of the charge-separated state of a zinc phthalocyanine-perylenebisimide dyad is decreased by binding of metal ions to the radical anion moiety in order to be lower than the triplet excited state. This results in formation of a long-lived charge-separated state. The mechanistic viability of formation of long-lived charge-separated states is demonstrated by a variety of examples based on the Marcus theory of electron transfer.

Femtosecond laser pulse control of electron transfer processes

Laser-pulse guided ultrafast electron transfer (ET) is studied theoretically for different types of donor–acceptor systems. The pulse initiates an optical transition from the electronic ground state into an excited state and controls the ET. The computations concentrate on systems where (a) the excited state (donor) is coupled to an acceptor level and where (b) the ET proceeds as an internal conversion from the excited state to the ground state. For both examples the manifold of vibrational coordinates is mapped on a single reaction coordinate coupled to a dissipative reservoir of further coordinates. Utilizing the methods of dissipative quantum dynamics combined with the optimal control (OC) scheme, it is demonstrated that control fields really exist which drive the ET in the required manner. Various properties of the OC algorithm are discussed when applied to dissipative dynamics and a scheme is proposed to avoid pinning in a local extremum.

Femtosecond dynamics and coherent control in atoms, molecules and clusters: Theory and experiments

The understanding and control of the dynamics in atoms, molecules and clusters has been a tremendously growing field in the past decade. This has been acknowledged with the 1999 Nobel prize in chemistry awarded to Ahmed Zewail. The present issue collects some of the newest theoretical and experimental results in the field of ultrafast dynamics and coherent control in the gas phase. The papers are grouped into three categories. The first section contains work on the “Coherent Control with Femtosecond Laser Pulses”. Topics like the general theory of quantum control, the control of electron transfer processes, transformation of chiral molecules and coherent population transfer are treated here. The “Femtosecond Dynamics” taking place in molecules and clusters is the topic of the second section. New insight into the nature of atomic motion within molecules and relaxation processes is provided. The last section collects most recent work on the interaction of ultrashort laser pulses with matter. In particular, high harmonic generation, multi-photon ionization and interference effects, as well as the possible orientation of molecules in external fields are discussed. We think that the present compilation demonstrates that the field of ultrashort pulse spectroscopy is of still growing importance and exciting new phenomena have been revealed in the past and will be discovered in the future.