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1.
Nat Commun ; 12(1): 2542, 2021 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-33953174

RESUMO

Lateral heterojunctions of atomically precise graphene nanoribbons (GNRs) hold promise for applications in nanotechnology, yet their charge transport and most of the spectroscopic properties have not been investigated. Here, we synthesize a monolayer of multiple aligned heterojunctions consisting of quasi-metallic and wide-bandgap GNRs, and report characterization by scanning tunneling microscopy, angle-resolved photoemission, Raman spectroscopy, and charge transport. Comprehensive transport measurements as a function of bias and gate voltages, channel length, and temperature reveal that charge transport is dictated by tunneling through the potential barriers formed by wide-bandgap GNR segments. The current-voltage characteristics are in agreement with calculations of tunneling conductance through asymmetric barriers. We fabricate a GNR heterojunctions based sensor and demonstrate greatly improved sensitivity to adsorbates compared to graphene based sensors. This is achieved via modulation of the GNR heterojunction tunneling barriers by adsorbates.

2.
Chirality ; 32(5): 619-631, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32155676

RESUMO

An enantiomerically pure (R)-2-methylpyrrolidine-based anilino squaraine crystallizes in two chiral polymorphs adopting a monoclinic C2 and an orthorhombic P21 21 21 structure, respectively. By various thin-film preparation techniques, a control of the polymorph formation is targeted. The local texture of the resulting textured thin films is connected to the corresponding optical properties. Special attention is paid to an unusual Davydov splitting, the anisotropic chiroptical response arising from preferred out-of-plane orientation of the crystallites, and the impact of the polymorph specific excitonic coupling.

3.
J Am Chem Soc ; 137(42): 13524-34, 2015 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-26414767

RESUMO

A series of nine dipolar merocyanine dyes has been studied as organic semiconductors in transistors and solar cells. These dyes exhibited single-crystal packing motifs with different dimensional ordering, which can be correlated to the performance of the studied devices. Hereby, the long-range ordering of the dyes in staircase-like slipped stacks with J-type excitonic coupling favors charge transport and improves solar cell performance. The different morphologies of transistor thin films and solar cell active layers were investigated by UV-vis, AFM, and XRD experiments. Selenium-containing donor-acceptor (D-A) dimethine dye 4 showed the highest hole mobility of 0.08 cm(2) V(-1) s(-1). BHJ solar cells based on dye 4 were optimized by taking advantage of the high crystallinity of the donor material and afforded a PCE of up to 6.2%.

4.
Nat Mater ; 14(4): 434-9, 2015 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-25532071

RESUMO

Structural order in organic solar cells is paramount: it reduces energetic disorder, boosts charge and exciton mobilities, and assists exciton splitting. Owing to spatial localization of electronic states, microscopic descriptions of photovoltaic processes tend to overlook the influence of structural features at the mesoscale. Long-range electrostatic interactions nevertheless probe this ordering, making local properties depend on the mesoscopic order. Using a technique developed to address spatially aperiodic excitations in thin films and in bulk, we show how inclusion of mesoscale order resolves the controversy between experimental and theoretical results for the energy-level profile and alignment in a variety of photovoltaic systems, with direct experimental validation. Optimal use of long-range ordering also rationalizes the acceptor-donor-acceptor paradigm for molecular design of donor dyes. We predict open-circuit voltages of planar heterojunction solar cells in excellent agreement with experimental data, based only on crystal structures and interfacial orientation.

5.
Dalton Trans ; 42(37): 13612-21, 2013 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-23900308

RESUMO

The synthesis, photophysical properties and application as emitters in solution-processed multi-layer organic light-emitting diodes (OLEDs) of a series of blue-green to red light-emitting phosphorescent platinum(II) complexes are reported. These complexes consist of phenylisoquinoline, substituted phenylpyridines or tetrahydroquinolines as C^N cyclometalating ligands and dipivaloylmethane as an ancillary ligand. Depending on both the structure of the C^N cyclometalating ligands and the dopant concentration in the matrix, these platinum(II) complexes exhibit different aggregation tendencies. This property affects the photoluminescence spectra of the investigated compounds and colour-stability of the fabricated OLEDs. Using the blue-green to yellow-green emitting complexes, the best results were obtained with the 2-(4-trifluoromethylphenyl)-5,6,7,8-tetrahydroquinoline based platinum(II) complex. A maximum luminous efficiency of 4.88 cd A(-1) and a power efficiency of 4.65 lm W(-1), respectively, were achieved. Employing the red emitting phenylisoquinoline based complex as an emitter, colour-stable and efficient (4.71 cd A(-1), 5.12 lm W(-1)) devices were obtained.


Assuntos
Luz , Compostos Orgânicos/química , Compostos Organoplatínicos/química , Estrutura Molecular , Compostos Organoplatínicos/síntese química , Processos Fotoquímicos
7.
Adv Mater ; 25(3): 437-42, 2013 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-22972396

RESUMO

The synthesis and full characterization of new platinum complexes bearing a bulky asymmetric dianionic tridentate ligand is reported. The hindrance of the ligand prevents detrimental intermolecular interactions yielding to highly emitting species in both crystalline state and thin-film. Such properties prompted their successful use in solution-processed OLEDs, showing remarkable external quantum efficiency up to 5.6%.

8.
Adv Mater ; 23(45): 5398-403, 2011 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-22021064

RESUMO

Thermal co-evaporation of C(60) fullerene and two merocyanine dyes affords bulk heterojunction solar cells with improved short-circuit currents and power conversion efficiencies in comparison with the respective single donor cells. These results are rationalized by the formation of three distinct subphases driven by differences in molecular shape and electrostatic interactions.


Assuntos
Fontes de Energia Elétrica , Eletricidade Estática , Luz Solar , Absorção , Análise Espectral
9.
Dalton Trans ; 40(43): 11629-35, 2011 Nov 21.
Artigo em Inglês | MEDLINE | ID: mdl-21960010

RESUMO

The structure-property correlations of a set of heteroleptic red- and green-emitting Ir(III) complexes with different temperature sensitivities and charge trapping capabilities are described, revealing superb performance in multi-layer phosphorescent organic light-emitting diodes (PhOLEDs) expressed by very high maximum luminous efficiencies up to 36.8 cd A(-1). Using 2-phenylpyridine and with 2-(naphthalen-1-yl)pyridine as the C^N ligand, the resulting red emitting complex featured a maximum luminous efficiency of 10.8 cd A(-1); one of the most excellent device performances within this class of red Ir(III) emitters.

11.
Adv Mater ; 22(37): 4193-7, 2010 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-20512818

RESUMO

Identically configured bulk heterojunction organic solar cells based on merocyanine dye donor and fullerene acceptor compounds (see figure) are manufactured either from solution or by vacuum deposition, to enable a direct comparison. Whereas the former approach is more suitable for screening purposes, the latter approach affords higher short-circuit current density and power conversion efficiency.


Assuntos
Corantes Fluorescentes/química , Pirimidinonas/química , Energia Solar , Compostos Bicíclicos Heterocíclicos com Pontes/química , Fulerenos/química , Polímeros/química , Poliestirenos/química , Teoria Quântica
13.
Org Biomol Chem ; 7(17): 3499-504, 2009 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-19675906

RESUMO

The anion chemosensor 1 based on a urea-activated phthalimide with a stereogenic centre was synthesized using an efficient procedure involving a Curtius rearrangement. Its photophysical properties were estimated in several solvents. Sensor 1 detected fluoride with absorption as well as fluorescence changes and was only observable for this case and not for other halides. The appearance of a new CT complex emission at a longer wavelength and no changes in the singlet lifetime of 1 in the presence of fluoride supported a fluorescence static quenching mechanism. 1H-NMR studies, together with theoretical calculations based on DFT methods at the B3lYP/6-31G* level of theory confirmed the formation of a [1-F]- complex through H-bonding interactions rather than receptor deprotonation in the recognition process. Reversibility of this process was observed upon addition of a protic solvent.


Assuntos
Fluoretos/análise , Ftalimidas/química , Ligação de Hidrogênio , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Solventes , Estereoisomerismo , Relação Estrutura-Atividade , Ureia/química
14.
J Org Chem ; 74(7): 2718-25, 2009 Apr 03.
Artigo em Inglês | MEDLINE | ID: mdl-19260697

RESUMO

The efficient synthesis of novel beta-diketonates equipped with functional carbazolyl moieties and their subsequent transformations in 5-hexyl-thienyl substituted carbazole derivatives is presented by utilizing an effective Stille cross-coupling reaction. The introduced beta-diketonates served as ancillary ligands for novel heteroleptic red- and green-emitting Ir(III) complexes, when combined with 2-(naphthalen-1-yl)pyridine and 2-phenylpyridine as cyclometalating ligands. These novel Ir(III) complexes revealed color-tunability and a very good thermal stability until at least 207 degrees C. In polystyrene blends, the heteroleptic Ir(III) complexes revealed remarkable quantum yields up to 36% and suitably short phosphorescence lifetimes ranging from 1 to 4 micros. In the case of the orange-red Ir(III) emitter, equipped with 2-(naphthalen-1-yl)pyridine cyclometallating ligands, a luminous efficiency as high as 7.7 cd/A at 7.4 V was achieved. All fabricated diodes exhibited in addition favorable color stability.

15.
Chemphyschem ; 9(5): 666-88, 2008 Apr 04.
Artigo em Inglês | MEDLINE | ID: mdl-18383220

RESUMO

Herein, we focus on the principles of photoconduction in random semiconductors-the key processes being optical generation of charge carriers and their subsequent transport. This is not an overview of the current work in this area, but rather a highlight of elementary processes, their involvement in modern devices and a summary of recent developments and achievements. Experimental results and models are discussed briefly to visualize the mechanism of optical charge generation in pure and doped organic solids. We show current limits of models based on the Onsager theory of charge generation. After the introduction of experimental techniques to characterize charge transport, the hopping concept for transport in organic semiconductors is outlined. The peculiarities of the transport of excitons and charges in disorderd organic semiconductors are highlighted. Finally, a short discussion of ultrafast transport and single chain transport completes the review.

16.
Phys Rev Lett ; 89(10): 107401, 2002 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-12225224

RESUMO

Electric field-assisted charge carrier photogeneration in a ladder-type methyl-substituted poly(paraphenylene) was investigated by ultrafast absorption spectroscopy at low excitation intensity. The dissociation of excitons into electron-hole pairs occurs from the vibrationally relaxed excited state throughout its lifetime and is caused by the applied electric field, rather than by existence of special "dissociation sites." These findings are of importance for material choice in device applications.

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