Structurally defined graphene nanoribbons (GNRs) have emerged as promising candidates for nanoelectronic devices. Low band gap (<1 eV) GNRs are particularly important when considering the Schottky ...barrier in device performance. Here, we demonstrate the first solution synthesis of 8‐AGNRs through a carefully designed arylated polynaphthalene precursor. The efficiency of the oxidative cyclodehydrogenation of the tailor‐made polymer precursor into 8‐AGNRs was validated by FT‐IR, Raman, and UV/Vis‐near‐infrared (NIR) absorption spectroscopy, and further supported by the synthesis of naphtho1,2,3,4‐ghiperylene derivatives (1 and 2) as subunits of 8‐AGNR, with a width of 0.86 nm as suggested by the X‐ray single crystal analysis. Low‐temperature scanning tunneling microscopy (STM) and solid‐state NMR analyses provided further structural support for 8‐AGNR. The resulting 8‐AGNR exhibited a remarkable NIR absorption extending up to ∼2400 nm, corresponding to an optical band gap as low as ∼0.52 eV. Moreover, optical‐pump TeraHertz‐probe spectroscopy revealed charge‐carrier mobility in the dc limit of ∼270 cm2 V−1 s−1 for the 8‐AGNR.
N=8 armchair graphene nanoribbons (AGNRs) were successfully synthesized in solution utilizing a custom arylated polynaphthalene precursor. The resulting 8‐AGNR exhibits a noteworthy near‐infrared absorption profile which signifies an exceptionally low optical band gap of 0.52 eV and demonstrates a record high dc charge‐carrier mobility of up to 270 cm2 V−1 s−1.
Efficient photoinduced electron transfer was observed across a 10cycloparaphenylene (10CPP) moiety that serves as a rigid non‐covalent bridge between a zinc porphyrin and a range of fullerenes. The ...preparation of iodo‐10CPP is the key to the synthesis of a porphyrin–10CPP conjugate, which binds C60, C70, (C60)2, and other fullerenes (KA>105 m−1). Fluorescence and pump–probe spectroscopy revealed intramolecular energy transfer between CPP and porphyrin and also efficient charge separation between porphyrin and fullerenes, affording up to 0.5 μs lifetime charge‐separated states. The advantage of this approach towards electron donor–acceptor dyads is evident in the case of dumbbell‐shaped (C60)2, which gave intricate charge‐transfer behavior in 1:1 and 2:1 complexes. These results suggest that 10CPP and its cross‐coupled derivatives could act as supramolecular mediators of charge transport in organic electronic devices.
Modular dyads: The successful synthesis of iodo‐10CPP allowed the study of photoinduced electron transfer in unusual supramolecular porphyrin–10CPP⊃fullerene complexes.
On‐surface Ullmann coupling is an established method for the synthesis of 1D and 2D organic structures. A key limitation to obtaining ordered polymers is the uncertainty in the final structure for ...coupling via random diffusion of reactants over the substrate, which leads to polymorphism and defects. Here, a topotactic polymerization on Cu(110) in a series of differently‐halogenated para‐phenylenes is identified, where the self‐assembled organometallic (OM) reactants of diiodobenzene couple directly into a single, deterministic product, whereas the other precursors follow a diffusion driven reaction. The topotactic mechanism is the result of the structure of the iodine on Cu(110), which controls the orientation of the OM reactants and intermediates to be the same as the final polymer chains. Temperature‐programmed X‐ray photoelectron spectroscopy and kinetic modeling reflect the differences in the polymerization regimes, and the effects of the OM chain alignments and halogens are disentangled by Nudged Elastic Band calculations. It is found that the repulsion or attraction between chains and halogens drive the polymerization to be either diffusive or topotactic. These results provide detailed insights into on‐surface reaction mechanisms and prove the possibility of harnessing topotactic reactions in surface‐confined Ullmann polymerization.
Real‐time spectroscopy and computed reaction pathway investigations of on‐surface Ullmann reaction of a series of aryl halides reveals topotactic kinetics in the formation of poly‐para phenylene chains, which is driven by alignment of reaction sites instead of random diffusion of the organic species.
Hemithioindigo (HTI) photoswitches have a tremendous potential for biological and supramolecular applications due to their absorptions in the visible‐light region in conjunction with ultrafast ...photoisomerization and high thermal bistability. Rational tailoring of the photophysical properties for a specific application is the key to exploit the full potential of HTIs as photoswitching tools. Herein we use time‐resolved absorption spectroscopy and Hammett analysis to discover an unexpected principal limit to the photoisomerization rate for donor‐substituted HTIs. By using stationary absorption and fluorescence measurements in combination with theoretical investigations, we offer a detailed mechanistic explanation for the observed rate limit. An alternative way of approaching and possibly even exceeding the maximum rate by multiple donor substitution is demonstrated, which give access to the fastest HTI photoswitch reported to date.
An unexpected principal limit to the photoisomerization rate for donor‐substituted hemithioindigos (HTIs; see figure) has been discovered; this provides a quantitative estimate for the highest possible photoisomerization rate. A mechanistic explanation for the observed limit is offered together with an alternative way of approaching the maximum rate by multiple donor substitution. This approach gave access to the fastest HTI photoswitch reported to date.
Molecular absorption and photoelectron spectra can be efficiently predicted with real-time time-dependent density functional theory. We show herein how these techniques can be easily extended to ...study time-resolved pump-probe experiments, in which a system response (absorption or electron emission) to a probe pulse is measured in an excited state. This simulation tool helps with the interpretation of fast-evolving attosecond time-resolved spectroscopic experiments, in which electronic motion must be followed at its natural timescale. We show how the extra degrees of freedom (pump-pulse duration, intensity, frequency, and time delay), which are absent in a conventional steady-state experiment, provide additional information about electronic structure and dynamics that improve characterization of a system. As an extension of this approach, time-dependent 2D spectroscopy can also be simulated, in principle, for large-scale structures and extended systems.
The decatungstate anion W10O324– is a widely used photocatalyst for promoting hydrogen atom transfer (HAT) reactions. The mechanism implicated in the activation of organic substrates, however, still ...needs to be clarified and has been claimed to involve an unknown relaxed excited state of triplet multiplicity, tagged wO. A subpicosecond investigation allowed us to follow early events leading to the chemically reactive species. A hot singlet excited state (S1 HOT) has been individuated through pump–probe experiments, yielding S1 by ultrafast decay (<1 ps). The reactive species wO arises from S1 in competition with decay to S0 (efficiency ca. 0.5) and has been detected spectroscopically by flash photolysis experiments, with peculiar absorption bands in the near-UV (370 nm) and visible (600–800 nm) regions. TD-DFT calculations demonstrated that excitation to S1 occurs through a ligand to metal charge transfer (LMCT) transition, involving a displacement of electron density from dicoordinated (bridging) oxygen to tungsten atoms. Population of wO ensues and involves a reorganization of the singly occupied orbital centered on oxygen (not tungsten) atoms. As a result, monocoordinated O centers acquire a partial radical character that well explains the known chemistry, essentially hydrogen atom transfer (HAT), and highlights the similarity with nπ* carbonyl triplets. This rationalization may help in devising other photocatalysts able to promote HAT processes from unactivated precursors.
In this work the software application called Glotaran is introduced as a Java-based graphical user interface to the R package TIMP, a problem solving environment for fitting superposition models to ...multi-dimensional data. TIMP uses a command-line user interface for the interaction with data, the specification of models and viewing of analysis results. Instead, Glotaran provides a graphical user interface which features interactive and dynamic data inspection, easier -- assisted by the user interface -- model specification and interactive viewing of results. The interactivity component is especially helpful when working with large, multi-dimensional datasets as often result from time-resolved spectroscopy measurements, allowing the user to easily pre-select and manipulate data before analysis and to quickly zoom in to regions of interest in the analysis results. Glotaran has been developed on top of the NetBeans rich client platform and communicates with R through the Java-to-R interface Rserve. The background and the functionality of the application are described here. In addition, the design, development and implementation process of Glotaran is documented in a generic way.
Electron transfer can readily occur over long (≥15 Å) distances. Usually reaction rates decrease with increasing distance between donors and acceptors, but theory predicts a regime in which ...electron‐transfer rates increase with increasing donor–acceptor separation. This counter‐intuitive behavior can result from the interplay of reorganization energy and electronic coupling, but until now experimental studies have failed to provide unambiguous evidence for this effect. We report here on a homologous series of rigid rodlike donor‐bridge‐acceptor compounds in which the electron‐transfer rate increases by a factor of 8 when the donor–acceptor distance is extended from 22.0 to 30.6 Å, and then it decreases by a factor of 188 when the distance is increased further to 39.2 Å. This effect has important implications for solar energy conversion.
Usually electron‐transfer rates decrease with increasing separation between the donor and the acceptor. However, the interplay between reorganization energy and electronic coupling can lead to opposite, counter‐intuitive behavior.
Photoluminescence characteristics of Gd2O3:Bi are studied in the 4.2–800 K temperature range by the time-resolved spectroscopy methods. Purely cubic structure of Gd2O3:Bi is confirmed by XRD. The ...luminescence of Bi3+(S6) and Bi3+(C2) centers is found to arise from the electron transitions from the emitting level of the triplet excited state of Bi3+, corresponding to the 3P1 → 1S0 transitions of the free Bi3+ ion. Relaxation processes in the triplet excited state of Bi3+ ions do not result in the population of the lowest-energy metastable level. The absence of the radiative transitions, corresponding to the 3P0 → 1S0 transitions of the free Bi3+ ion, explains the short (0.3–2.0 μs) decay time of the triplet emission of Bi3+ even at 4.2 K. The conclusion is made that the fast luminescence decay cannot be caused by the mixing of the metastable and emitting levels of the triplet excited state of Bi3+ by the magnetic field created at the Bi3+ site by the magnetically ordered Gd3+ sublattice. The electron transfer and recombination processes, resulting in the appearance of the photo- and thermally stimulated electron recombination luminescence of Bi3+(S6) and Bi3+(C2) centers under excitation in the Eexc > 4.3 eV energy region, are also discussed. The energy level positions of the Bi3+(S6) and Bi3+(C2) centers in the band gap of Gd2O3 are estimated.
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•Photo- and thermoluminescence and XRD are studied for Gd2O3:Bi3+ powder.•Luminescence arises only from the 3P1 .→ 1S0 transitions of Bi3+(S6) and Bi3+(C2)•This explains a short (∼10−6 s) decay time of the triplet luminescence at 4.2 K.•Fast decay cannot be caused by the magnetic field created at Bi3+ site by Gd3+ sublattice.•Electron transfer processes take place under excitation of Bi3+ with Eexc>4.3 eV.
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