Probing molecular wires: synthesis, structural, and electronic study of donor-acceptor assemblies exhibiting long-range electron transfer

A series of donor-acceptor arrays (C60-oligo-PPV-exTTF; 16-20) incorporating pi-conjugated oligo(phenylenevinylene) wires (oligo-PPV) of different length between pi-extended tetrathiafulvalene (exTTF) as electron donor and C60 as electron acceptor has been prepared by multistep convergent synthetic approaches. The electronic interactions between the three electroactive species present in 16-20 were investigated by UV-visible spectroscopy and cyclic voltammetry (CV). Our studies clearly show that, although the C60 units are connected to the exTTF donors through a pi-conjugated oligo-PPV framework, no significant electronic interactions are observed in the ground state. Interestingly, photoinduced electron-transfer processes over distances of up to 50 Angstroms afford highly stabilized radical ion pairs. The measured lifetimes for the photogenerated charge-separated states are in the range of hundreds of nanoseconds (approximately 500 ns) in benzonitrile, regardless of the oligomer length (i.e., from the monomer to the pentamer). A different lifetime (4.35 micros) is observed for the heptamer-containing array. This difference in lifetime has been accounted for by the loss of planarity of the oPPV moiety that increases with the wire length, as established by semi-empirical (PM3) theoretical calculations carried out with 19 and 20. The charge recombination dynamics reveal a very low attenuation factor (beta = 0.01 +/- 0.005 Angstroms(-1)). This beta value, as well as the strong electron coupling (V approximately 5.5 cm(-1)) between the donor and the acceptor units, clearly reveals a nanowire behavior for the pi-conjugated oligomer, which paves the way for applications in nanotechnology.     

An introduction to molecular spintronics

We review the progress and future possibilities in the emerging area of molecular spintronics. We first provide an overview of the different transport regimes in which electronic nanodevices can operate, then briefly overview the important characteristics of molecular magnetic materials that can be useful for application in spintronics and we eventually present several schemes to include such systems into spintronic nanodevices. We hightlight the importance of a chemical approach to the area, and in the last section we showcase some approaches to the creation of hybrids made of carbon nanostructures and molecular magnets, which are gaining increasing attention.     

Suppression of efficiency roll-off in TADF-OLEDs using Ag-island nanostructures with localized surface plasmon resonance effect

Organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) have emerged as promising alternatives to phosphorescent OLEDs for harvesting both singlet and triplet excitons. However, the development of TADF-OLEDs meets a thorny problem of serious efficiency roll-off at high luminance. Here, we demonstrate an approach to suppress the efficiency roll-off characteristics in TADF-OLEDs by localized surface plasmon resonance (LSPR) effect of easy-fabricated Ag-island nanostructures. Compared with the common TADF-OLEDs at a high current density of 100 mA cm⁻², the efficiency roll-off ratio of the TADF-OLEDs with Ag-island nanostructures decreases from 49.75% to 35.76% significantly, and the maximum current efficiency is increased by 10.5%. The performance enhancement is mainly attributed to the coupling between excitons and localized surface plasmons (LSPs), which could alter the excited state kinetic characteristics of TADF molecules.