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| 2. |
- Aderne, Rian E., et al.
(författare)
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On the energy gap determination of organic optoelectronic materials : the case of porphyrin derivatives
- 2022
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Ingår i: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; :3, s. 1791-1803
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Tidskriftsartikel (refereegranskat)abstract
- The correct determination of the ionization potential (IP) and electron affinity (EA) as well as the energy gap is essential to properly characterize a series of key phenomena related to the applications of organic semiconductors. For example, energy offsets play an essential role in charge separation in organic photovoltaics. Yet there has been a lot of confusion involving the real physical meaning behind those quantities. Experimentally the energy gap can be measured by direct techniques such as UV-Vis absorption, or indirect techniques such as cyclic voltammetry (CV). Another spectroscopic method is the Reflection Electron Energy Loss Spectroscopy (REELS). Regarding data correlation, there is little consensus on how the REELS' energy gap can be interpreted in light of the energies obtained from other methodologies such as CV, UV-Vis, or photoemission. In addition, even data acquired using those traditional techniques has been misinterpreted or applied to derive conclusions beyond the limits imposed by the physics of the measurement. A similar situation also happens when different theoretical approaches are used to assess the energy gap or employed to explain outcomes from experiments. By using a set of porphyrin derivatives as model molecules, we discuss some key aspects of those important issues. The peculiar properties of these porphyrins demonstrate that even straightforward measurements or calculations performed in a group of very similar molecules need a careful interpretation of the outcomes. Differences up to 660 meV (similar to 190 meV) are found comparing REELS (electrochemical) measurements with UV-Vis energy gaps, for instance. From the theoretical point of view, a reasonable agreement with electrochemical measurements of the IP, EA, and the gap of the porphyrins is only obtained when the calculations involve the full thermodynamics of the redox processes. The purpose of this work is to shed light on the differences and similarities of those aforementioned characterization methods and provide some insight that might help one to develop a critical analysis of the different experimental and theoretical methodologies.
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- Damas, Giane, et al.
(författare)
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Symmetric Small-Molecules With Acceptor-Donor-Acceptor Architecture for Efficient Visible-Light Driven Hydrogen Production : Optical and Thermodynamic Aspects
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:51, s. 30799-30808
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Tidskriftsartikel (refereegranskat)abstract
- Small-molecules (SM) have attracted a great deal of attention in the field of solar energy conversion due to their unique propertiescompared to polymers, such as well-defined molecular weight and lack of regio-isomeric impurities. Furthermore, these materials can be synthesized in a variety of configurational architectures, representing an opportunity for tailoring chemical and optical properties that could lead to a better photocatalytic efficiency for hydrogen generation. Here, we evaluate by means of density functional theory (DFT) and time-dependent DFT methods a set of small-molecules with A-D-A architecture (A-acceptor; D- donor) based on well-known building blocks like thiophene (T), cyclopentadithiophene (CPT) and benzothiadiazole (BT) as potential candidates for photocatalytic hydrogen evolution reaction (HER). We also propose i) the replacement of the thiophene unit by 3,4-ethylenedioxythiophene (EDOT) to form with CPT unit an extended donor core ii) an additional acceptor unit, the 1,3,4-thiadiazole (Tz), in the extremities and iii) insertion of the difluoromethoxy (DFM) as substituent in the BT unit. Our outcomes reveal that these materials have a broad absorption spectrum with λ= 318-719 nm, being the most intense absorption peak originated from an electronic transition with charge-transfer nature, as the spatial distribution of LUMO is concentrated on the acceptor units for all materials. Moreover, these small-molecules not only present catalytic power or thermodynamic driving force to carry out the chemical reactions involved in the process of hydrogen production, but can be coupled in cooperative photocatalytic systems to promote intramolecular charge transfer that is expected to boost the overall photocatalytic efficiency of these materials.
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| 6. |
- Friedlein, Rainer, et al.
(författare)
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Surface-induced vertical alignment of self-assembled supramolecular columns of large polycyclic aromatic hydrocarbons and porphyrins
- 2004
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Ingår i: Synthetic metals. - : Elsevier BV. - 0379-6779 .- 1879-3290. ; 147:01-Mar, s. 79-83
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Tidskriftsartikel (refereegranskat)abstract
- Ordered films of polycyclic aromatic hydrocarbons (PAHs) and porphyrins with functional (e.g. thiophene) side-groups are good candidates for (opto-)electronic applications where fast charge separation and transport are required. Such highly ordered thin films of PAHs, including discotic hexa-peri-hexabenzocoronene (HBC) and C-132-C-16,C-4, as well as brominated functionalized porphyrin molecules have been grown from solutions on semi-metallic molybdenum disulfide substrates and characterized by angle-resolved valence band photoelectron spectroscopy. A vertical growth of self-assembled supramolecular columns perpendicular to the basal plane of the substrate along with their lateral ordering on the surface has been achieved. Annealing made it possible to increase the structural order in the HBC columns, with molecules positioned at a regular offset from the columnar axis. This permitted the formation of extended pi-electronic states with a bandwidth of at least 0.1-0.2 eV at room temperature. (C) 2004 Elsevier B.V. All rights reserved.
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| 7. |
- von Kieseritzky, Fredrik
(författare)
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NEW OLIGOTHIOPHENES
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with synthesis and characterization of newoligothiophenes and derivatives thereof, for use as organicsemiconductors in optical and electronic applications, such asfield-effect transistors and light-emitting diodes. Much workis devoted to the development of new synthetic strategies forinteresting building blocks, to beused for synthesizing suchmaterials. One series of regio-defined oligothiophenes, up tothe octamer, has been prepared and evaluated. Photoluminescencequantum efficiencies of these were 22-31 % in solution, butdropped to 2-5 % in the solid state. Another project deals withthe development of oligothiophenes with in-chain chirality.These may find use in polarized lightemitting diodes. Finally,two oligothienyl-substituted porphyrins have been synthesizedand are currently evaluated for use in light-emitting diodesand possibly in solar cells.
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| 8. |
- von Kieseritzky, Fredrik, 1975-
(författare)
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New Oligothiophenes
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with synthesis and characterization of newoligothiophenes and derivatives thereof, for use insemiconductor applications. One series of regiodefinedoligothiophenes up to the octamer was prepared and evaluated.Photoluminescence quantum efficiencies in solution were 22-31%, but dropped to 2-5 % in the solid state. One oligothiophenein this series was evaluated as a new matrix for MALDI-TOF,with promising results. Another project deals with developmentof oligothiophenes with "in-chain" chirality, which may finduse in polarizing light-emitting diodes.Oligothiophene-porphyrin hybrid materials were synthesized forevaluation as active components in light-producing and/or-harvesting devices. Finally, a novel and simplified synthesisof EDOT, which is a major monomer in oligothiophene chemistry,is presented.
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| 9. |
- Woldegiorgis, Andreas, et al.
(författare)
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Polymer-assisted laser desorption/ionization analysis of small molecular weight compounds
- 2004
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Ingår i: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 18:8, s. 841-852
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Tidskriftsartikel (refereegranskat)abstract
- The use of non-polar, small polymers as matrices for the analysis of low molecular weight compounds in polymer-assisted laser desorption/ionization mass spectrometry (PALDI-MS) is demonstrated. The matrices evaluated were either based on an oligothiophene or a benzodioxin backbone. Metallocenes, polycyclic hydrocarbons, a fluorosurfactant, and a subset of small organic compounds with various functionalities, served as model analytes. The mechanism of ionization charge transfer is discussed and ionization potentials for the matrices in the study have been estimated using density functional theory (DFT) calculations. Some of the results are possibly contradictory to the generally accepted limiting conditions for gas-phase charge-transfer reactions. These results are interpreted in the light of energy pooling. Also a new mass calibration procedure for the lowmass region in positive ion mode is presented, and some aspects of the ionization/desorption process leading to radical cations are studied.
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| 10. |
- Wouk de Menezes, Luana Cristina, et al.
(författare)
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Nonradiative Energy Transfer between Porphyrin and Copolymer in Films Processed by Organic Solvent and Water-Dispersible Nanoparticles with Photovoltaic Applications
- 2018
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:10, s. 5796-5804
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Tidskriftsartikel (refereegranskat)abstract
- In organic photovoltaic (OPV) devices, one way to increase light harvesting is to combine materials with complementary absorptions. However, the physical properties behind this process, such as Forster resonance energy transfer (FRET), remain elusive. A mixture of the metalloporphyrin Zn(SBrTTP) and the donor acceptor copolymer PSiF-DBT in films processed by organic solvent and water-soluble nanoparticles was investigated, and the energy transfer rate was correlated to the bilayer of an OPV device with a fullerene derivative (C-70). Using steady-state and time-resolved emission studies, the FRET from the porphyrin to the copolymer was observed and found to be highest in the film processed by organic solvent treatment at 100 degrees C. The devices processed by organic solvents showed superior performance to blended materials when treated at 100 degrees C, increasing the current without reducing open-circuit voltage. In nanoparticle systems, we observed that, with a smaller distance between the materials, higher FRET is performed. The device's performance showed higher current as the materials were closer together. To go beyond materials with complementary absorption, the optimization of energy transfer between them might be a promising way to increase charge generation in photovoltaic devices with different morphologies.
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