Molecular wires – impact of π-conjugation and implementation of molecular bottlenecks

Abstract

In this review we highlight recent progress in the field of photochemically and thermally induced electron transport through molecular bridges as integrative parts of electron donor-bridge-acceptor conjugates. The major emphasis is hereby on the design and the modular composition of the bridges. To this end, we will demonstrate that control over attenuation factors and reorganization energies, on one hand, as well as electronic and electron-vibration couplings, on the other hand, enables tuning electron transport over distances as short as 3.5 Å and as large as 50 Å by up to nine orders of magnitude. In terms of electron transport, the maximum extreme is given by carbon-bridged oligo-p-phenylenevinylenes of different lengths, while a zinc tetraphenylporphyrin free base tetraphenylporphyrin dyad constitutes the minimum extreme.

Radical Cation π‐Dimers of Conjugated Oligomers as Molecular Wires: An Analysis Based on Nitronyl Nitroxide Spin Labels

“…[4,5] Molecular wires for molecular electronic devices mediate electron or charget ransport, and typicallyc onsist of linear p-conjugated systems. [6][7][8][9][10][11][12] In addition to covalently linked p-conjugated bridges, the effects of hydrogen bonds, [13][14][15] metal-metal interactions, [16][17][18] and coordination bonds [16,19,20] on molecular wire properties have also been investigated. Thesew eak bonds are beneficial for constructing self-assembled systems and as conventional intermolecular interactions in supramolecular chemistry.R ecently,a sa ne merging weak interaction, the use of long-bonded dimers of stable radical ions, [21,22] the so-called p-dimers,h as been expanded to control molecular motion [23] and to construct supramolecular architectures.…”

Charge-Gating Dibenzothiophene-S,S-dioxide Bridges in Electron Donor–Bridge–Acceptor Conjugates

“…Both electron and hole-transfer are likely to be operative. In stark contrast, placing the S unit in the center of the bridge with one Fl unit adjacent to ZnP and one adjacent to C 60 (20), either blocks or activates the charge-separated state formation on 24 photoexcitation of ZnP or C 60 , respectively. In other words, unidirectional charge transfer is only possible for holes, but not for electrons because of the electron-withdrawing nature of the S unit.…”

“…[12][13][14][15] It is, therefore, of paramount importance to understand the effects of systematically varying the chemical structure and length of the bridge in new DBA systems, where the bridge mediates the electronic coupling between donor-and acceptor moieties over large distances. 4, [16][17][18][19][20][21][22][23][24] Coupling typically decays exponentially with increasing distance between the D and A termini, 25 as reflected by the electron-transfer rate constant k ET . Thus, the rates of charge separation and recombination are characterized by …”

Efficient Photoinduced Energy and Electron Transfer in ZnII–Porphyrin/Fullerene Dyads with Interchromophoric Distances up to 2.6 nm and No Wire‐like Connectivity

“…In contrast, an intramolecular energy transfer has been observed in apolart oluene. It is therefore interesting to compare the photophysical behavior of the present systems with previousp orphyrin-fullerene dyads, which are typicallyc haracterized by fully conjugated ("wiretype") bridges [13,31,32] or short-range through-space interactions. [29,34,50,51] Although the influence of the solvent polarity on the deactivation pathways upon the photoexcitation of the conjugate F-P-F has been elucidated, the lack of conformational control prevented us to assess the influence of the interchromophoric distance or the relative orientation of the individual parts.…”