| 1. |
- Edvinsson, Tomas, et al.
(författare)
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Intramolecular charge-transfer tuning of perylenes : Spectroscopic features and performance in Dye-sensitized solar cells
- 2007
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 111:42, s. 15137-15140
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Tidskriftsartikel (refereegranskat)abstract
- Five novel perylene molecules with different intramolecular charge-transfer (ICT) characters have been synthesized. The relation between the ICT character for different donating groups and the results for their electro- and photochemical properties as well as their performance in nanostructured dye-sensitized solar cells (nDSC) are reported. With the stronger donors, we obtain a shift of the lowest unoccupied molecular orbital (LUMO) to more negative potential versus normal hydrogen electrode (NHE) as well as an increase the charge separation in the dye upon excitation. Ab initio calculations were used to analyze the effects on orbital energies and electron distribution with the different donors. Incorporating the dyes in nDSCs, we see a drastical improvement in the performance for the more polar dyes. In particular, we find a much improved photovoltage because of higher LUMO levels, allowing conduction band tuning in the TiO2 as well as a contribution from the permanent dipoles in the dyes. The photocurrent improves remarkably with increasing ICT character of the dyes. The external quantum efficiency reached over 70%, and the overall solar-to-electrical energy conversion efficiency was improved to almost 4% for the dye with highest ICT character, which can be compared with devices with the standard N719 dye (Ru(dcbPY)(2)(NCS)(2)) showing 6% under similar conditions. The performance is a significant improvement compared to previous reports for perylenes and lifts the performance from modest to promising. Initial stability tests show that the dye with the highest performance was spectrally stable after more than 2000 h of irradiation in a solar-cell device.
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| 2. |
- Liscio, Andrea, et al.
(författare)
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Local Surface Potential of pi-Conjugated Nanostructures by Kelvin Probe Force Microscopy: Effect of the Sampling Depth
- 2011
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Ingår i: SMALL. - : John Wiley and Sons, Ltd. - 1613-6810. ; 7:5, s. 634-639
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Tidskriftsartikel (refereegranskat)abstract
- Kelvin probe force microscopy (KPFM) is usually applied to map the local surface potential of nanostructured materials at surfaces and interfaces. KPFM is commonly defined as a surface technique, even if this assumption is not fully justified. However, a quantification of the surface sensitivity of this technique is crucial to explore electrical properties at the nanoscale. Here a versatile 3D model is presented which provides a quantitative explanation of KPFM results, taking into account the vertical structure of the sample. The model is tested on nanostructured films obtained from two relevant semiconducting systems for field-effect transistor and solar cell applications showing different interfacial properties, i.e., poly(3-hexylthiophene) (P3HT) and perylene-bis-dicarboximide (PDI). These findings are especially important since they enable quantitative determination of the local surface potential of conjugated nanostructures, and thereby pave the way towards optimization of the electronic properties of nanoscale architectures for organic electronic applications.
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| 3. |
- Liu, Junzhi, et al.
(författare)
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Fused Dibenzo[a,m]rubicene : A New Bowl-Shaped Subunit of C-70 Containing Two Pentagons
- 2016
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 138:27, s. 8364-8367
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Tidskriftsartikel (refereegranskat)abstract
- Total synthetic approaches of fullerenes are the holy grail for organic chemistry. So far, the main attempts have focused on the synthesis of the buckmin-sterfullerene C-60. In contrast, access to subunits of the homologue C-70 remains challenging. Here, we demonstrate an efficient bottom-up strategy toward a novel bowl-shaped polycyclic aromatic hydrocarbons (PAH) C34 with two pentagons. This PAH represents a subunit for C-70 and of other higher fullerenes. The bowl-shaped structure was unambiguously determined by X-ray crystallography. A bowl-to-bowl inversion for a C-70 fragment in solution was investigated by dynamic NMR analysis, showing a bowl-to-bowl inversion energy (Delta G double dagger) of 16.7 kcal mol(-1), which is further corroborated by DFT calculations.
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| 4. |
- Parvez, Khaled, et al.
(författare)
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Exfoliation of Graphite into Graphene in Aqueous Solutions of Inorganic Salts
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 136:16, s. 6083-6091
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Tidskriftsartikel (refereegranskat)abstract
- Mass production of high-quality graphene sheets is essential for their practical application in electronics, optoelectronics, composite materials, and energy-storage devices. Here we report a prompt electrochemical exfoliation of graphene sheets into aqueous solutions of different inorganic salts ((NH4)(2)SO4, Na2SO4, K2SO4, etc.). Exfoliation in these electrolytes leads to graphene with a high yield (greater than85%, less than= 3 layers), large lateral size (up to 44 mu m), low oxidation degree (a C/O ratio of 17.2), and a remarkable hole mobility of 310 cm(2) V-1 s(-1). Further, highly conductive graphene films (11 Omega sq(-1)) are readily fabricated on an A4-size paper by applying brush painting of a concentrated graphene ink (10 mg mL(-1), in N,N-dimethylformamide). All-solid-state flexible supercapacitors manufactured on the basis of such graphene films deliver a high area capacitance of 11.3 mF cm(-2) and an excellent rate capability of 5000 mV s(-1). The described electrochemical exfoliation shows great promise for the industrial-scale synthesis of high-quality graphene for numerous advanced applications.
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| 9. |
- Schwartz, Erik, et al.
(författare)
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"Helter-Skelter-Like" Perylene Polyisocyanopeptides
- 2009
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 15:11, s. 2536-2547
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Tidskriftsartikel (refereegranskat)abstract
- We report on a combined experimental and computational investigation on the synthesis and thorough characterization of the structure of perylene-functionalized polyisocyanides. Spectroscopic analyses and extensive molecular dynamics studies revealed a well defined 4, helix in which the perylene molecules form four "helter skelter-like" overlapping pathways along which excitons and electrons can rapidly migrate. The well-defined polymer scaffold stabilized by hydrogen bonding, to which the chromophores are attached, accounts for the precise architectural definition, and molecular stiffness observed for these molecules. Molecular-dynamics studies showed that the chirality present in these polymers is expressed in the formation of stable right-handed helices. The formation of chiral supramolecular structures is further supported by the measured and calculated bisignated Cotton effect. The structural definition of the chromophores aligned in one direction along the backbone is highlighted by the extremely efficient exciton migration rates and charge densities measured with Transient Absorption Spectroscopy.
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| 10. |
- Waeckerlin, Christian, et al.
(författare)
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Magnetic exchange coupling of a synthetic Co(II)-complex to a ferromagnetic Ni substrate
- 2013
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 49:91, s. 10736-10738
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Tidskriftsartikel (refereegranskat)abstract
- On-surface assembly of a spin-bearing and non-aromatic porphyrin-related synthetic Co(II)-complex on a ferromagnetic Ni thin film substrate and subsequent magnetic exchange interaction across the interface were studied by scanning tunnelling microscopy (STM), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and density functional theory +U (DFT + U) calculations.
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| 11. |
- Wang, Xiao-Ye, et al.
(författare)
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Exploration of pyrazine-embedded antiaromatic polycyclic hydrocarbons generated by solution and on-surface azomethine ylide homocoupling
- 2017
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Nanographenes, namely polycyclic aromatic hydrocarbons (PAHs) with nanoscale dimensions (amp;gt;1 nm), are atomically precise cutouts from graphene. They represent prime models to enhance the scope of chemical and physical properties of graphene through structural modulation and functionalization. Defined nitrogen doping in nanographenes is particularly attractive due to its potential for increasing the number of p-electrons, with the possibility of introducing localized antiaromatic ring elements. Herein we present azomethine ylide homocoupling as a strategy to afford internally nitrogen-doped, non-planar PAH in solution and planar nanographene on surfaces, with central pyrazine rings. Localized antiaromaticity of the central ring is indicated by optical absorption spectroscopy in conjunction with theoretical calculations. Our strategy opens up methods for chemically tailoring graphene and nanographenes, modified by antiaromatic dopants.
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| 12. |
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