Evaluation of Carbon Based Molecular Junctions as Practical Photosensors.

Molecular junctions with partially transparent top contacts permit monitoring photocurrents as probes of transport mechanism and potentially could act as photosensors with characteristics determined by the molecular layer inside the device. Previously reported molecular junctions containing nitroazobenzene (NAB) oligomers and oligomers of two different aromatic molecules in bilayers were evaluated for sensitivity, dark signal, responsivity, and limits of detection, in order to determine the device parameters which have the largest effects on photodetection performance. The long-range transport of photogenerated charge carriers permits the use of molecular layers thick enough to absorb a large fraction of the light incident on the layer.

Comment on "Extent of conjugation in diazonium-derived layers in molecular junction devices determined by experiment and modelling" by C. Van Dyck, A. J. Bergren, V. Mukundan, J. A. Fereiro and G. A. DiLabio, , 2019, , 16762.

Misinterpretation of scanning tunnelling microscopy results yielded incorrect conclusions about the flatness of a carbon electrode substrate used for molecular electronic devices. Furthermore, the results are not supported statistically and likely not representative of materials used in numerous publications.

Ion-Assisted Resonant Injection and Charge Storage in Carbon-Based Molecular Junctions.

Resonant injection and resulting charge storage were examined in a large-area carbon/tetraphenylporphyrin(TPP)/LiF/carbon junction, where the LiF layer provides mobile ions in acetonitrile (ACN) vapor. Resonant electron transfer into TPP molecules occurs at <+1 V in the presence of mobile ions, enabled by ionic screening of the carbon electrode. Injection of holes, i.

Bottom-up, Robust Graphene Ribbon Electronics in All-Carbon Molecular Junctions.

Large-area molecular electronic junctions consisting of 5-carbon wide graphene ribbons (GR) with lengths of 2-12 nm between carbon electrodes were fabricated by electrochemical reduction of diazotized 1,8-diaminonaphthalene. Their conductance greatly exceeds that observed for other molecular junctions of similar thicknesses, by a factor of >1 × 10 compared to polyphenylenes and >1 × 10 compared to alkane chains. The remarkable increase of conductance of the GR nanolayer results from (i) uninterrupted planarity of fused-arene structure affording extensive π-electron delocalization and (ii) enhanced electronic coupling of molecular layer with the carbon bottom contact by two-point covalent bonding, in agreement with DFT-based simulations.

Creation of Superheterojunction Polymers via Direct Polycondensation: Segregated and Bicontinuous Donor-Acceptor π-Columnar Arrays in Covalent Organic Frameworks for Long-Lived Charge Separation.

By developing metallophthalocyanines and diimides as electron-donating and -accepting building blocks, herein, we report the construction of new electron donor-acceptor covalent organic frameworks (COFs) with periodically ordered electron donor and acceptor π-columnar arrays via direct polycondensation reactions. X-ray diffraction measurements in conjunction with structural simulations resolved that the resulting frameworks consist of metallophthalocyanine and diimide columns, which are ordered in a segregated yet bicontinuous manner to form built-in periodic π-arrays. In the frameworks, each metallophthalocyanine donor and diimide acceptor units are exactly linked and interfaced, leading to the generation of superheterojunctions-a new type of heterojunction machinery, for photoinduced electron transfer and charge separation.

Graphene oxide-Li(+)@C60 donor-acceptor composites for photoenergy conversion.

An ionic endohedral metallofullerene (Li(+)@C60) with mild hydrophilic nature was combined with graphene oxide (GO) to construct a donor-acceptor composite in neat water. The resulting composite was characterised by UV-Vis and Raman spectroscopy, powder X-ray diffraction, dynamic light scattering measurements and transmission electron microscopy. Theoretical calculations (DFT at the B3LYP/6-31(d) level) were also utilized to gain further insight into the composite formation.

Long-lived charge separation in a rigid pentiptycene bis(crown ether)-Li(+)@C60 host-guest complex.

We report long-lived charge separation in a highly rigid host-guest complex of pentiptycene bis(crown ether) and Li(+)@C60, in which the pentiptycene framework is actively involved as an electron donor in a photoinduced electron-transfer process to the excited states of Li(+)@C60 through a rigid distance in the complex.

Photoinduced charge separation in ordered self-assemblies of perylenediimide-graphene oxide hybrid layers.

Remarkably fast photoinduced charge separation in well-ordered self-assemblies of perylenediimide-graphene oxide (TAIPDI-GO) hybrid layers was observed in aqueous environments. Slow charge recombination indicates an effective charge migration between the self-assembled layers of PDI-GO hybrids following the charge separation.

Robust inclusion complexes of crown ether fused tetrathiafulvalenes with Li⁺@C₆₀ to afford efficient photodriven charge separation.

Inclusion complexes of benzo- and dithiabenzo-crown ether functionalized monopyrrolotetrathiafulvalene (MPTTF) molecules were formed with Li(+)@C60(1⋅Li(+)@C60 and 2⋅Li(+)@C60). The strong complexation has been quantified by high binding constants that exceed 10(6) M(-1) obtained by UV/Vis titrations in benzonitrile (PhCN) at room temperature. On the basis of DFT studies at the B3LYP/6-311G(d,p) level, the orbital interactions between the crown ether moieties and the π surface of the fullerene together with the endohedral Li(+) have a crucial role in robust complex formation.

Tuning the photodriven electron transport within the columnar perylenediimide stacks by changing the π-extent of the electron donors.

Photodriven electron-transport properties of the self-assemblies of N,N'-di(2-(trimethylammoniumiodide)ethylene)perylenediimide stacks (TAIPDI)(n) with three electron donors, disodium 4,4'-bis(2-sulfonatostyryl)biphenyl (BSSBP, stilbene-420), sodium 9,10-dimethoxyanthracene-2-sulfonate (DANS) and disodium 6-amino-1,3-naphthalenedisulfonate (ANADS) have been studied in water. These electron donors vary in their π-extent to adjust the electronic coupling and the distance with the PDI stacks. Possessing the largest π-extent, BSSBP has strong π-π interactions as well as ionic interactions with (TAIPDI)(n).

Elongation of lifetime of the charge-separated state of ferrocene-naphthalenediimide-[60]fullerene triad via stepwise electron transfer.

Photoinduced electron-transfer processes of a newly synthesized rodlike covalently linked ferrocene-naphthalenediimide-[60]fullerene (Fc-NDI-C(60)) triad in which Fc is an electron donor and NDI and C(60) are electron acceptors with similar first one-electron reduction potentials have been studied in benzonitrile. In the examined Fc-NDI-C(60) triad, NDI with high molar absorptivity is considered to be the chromophore unit for photoexcitation. Although the free-energy calculations verify that photoinduced charge-separation processes via singlet- and triplet-excited states of NDI are feasible, transient absorption spectra observed upon femtosecond laser excitation of NDI at 390 nm revealed fast and efficient electron transfer from Fc to the singlet-excited state of NDI ((1)NDI*) to produce Fc(+)-NDI(•-)-C(60).

Syntheses, electrochemistry, and photodynamics of ferrocene-azadipyrromethane donor--acceptor dyads and triads.

A near-IR-emitting sensitizer, boron-chelated tetraarylazadipyrromethane, has been utilized as an electron acceptor to synthesize a series of dyads and triads linked with a well-known electron donor, ferrocene. The structural integrity of the newly synthesized dyads and triads was established by spectroscopic, electrochemical, and computational methods. The DFT calculations revealed a 'molecular clip'-type structure for the triads wherein the donor and acceptor entities were separated by about 14 Å.

Photochemical charge separation in closely positioned donor-boron dipyrrin-fullerene triads.

A series of molecular triads, composed of closely positioned boron dipyrrin-fullerene units, covalently linked to either an electron donor (donor(1)-acceptor(1)-acceptor(2)-type triads) or an energy donor (antenna-donor(1)-acceptor(1)-type triads) was synthesized and photoinduced energy/electron transfer leading to stabilization of the charge-separated state was demonstrated by using femtosecond and nanosecond transient spectroscopic techniques. The structures of the newly synthesized triads were visualized by DFT calculations, whereas the energies of the excited states were determined from spectral and electrochemical studies. In the case of the antenna-donor(1)-acceptor(1)-type triads, excitation of the antenna moiety results in efficient energy transfer to the boron dipyrrin entity.

A new cyanofluorene-triphenylamine copolymer: synthesis and photoinduced intramolecular electron transfer processes.

A new pi-conjugated copolymer, namely, poly{cyanofluore-alt-[5-(N,N'-diphenylamino)phenylenevinylene]} ((CNF-TPA)(n)), was synthesized by condensation polymerization of 2,2'-(9,9-dioctyl-9H-fluorene-2,7-diyl)diacetonitrile and 5-(N,N'-diphenylamino)benzene-1,3-dicarbaldehyde by using the Knoevenagel reaction. By design, diphenylamine, alkylfluorene and poly(p-phenylenevinylene) linkages were combined to form a (CNF-TPA)(n) copolymer which exhibits high thermal stability and glass-transition temperature. Photodynamic measurements in polar benzonitrile indicate fast and efficient photoinduced electron transfer ( approximately 10(11) s(-1)) from triphenylamine (TPA) to cyanofluorene (CNF) to produce the long-lived charge-separated state (90 mus).