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Papers by Daniel Egbe
Wood fuel is undoubtedly the main source of energy for cooking in sub-Saharan Africa as it repres... more Wood fuel is undoubtedly the main source of energy for cooking in sub-Saharan Africa as it represents more than three quarter of household energy consumption. The exploitation of wood for fuel purposes contributes to forest degradation. It is becoming urgent to diversify domestic energy sources. Substituting other forms of energy with traditional ones is extremely difficult due to low income of the population and culinary habits. In this context, ecological charcoal seems to be an attractive alternative to wood energy. Agricultural waste was collected, dried to a moisture content of less than 10%. Waste was pyrolysed and the resulting carbonaceous material mixed with a binder and extruded to form briquettes. Three binders were tested: starch, clay and arabic gum. The pyrolysis of biomass generated three byproducts: a solid (biochar), liquid and gaseous product. This process took 3 hours 45 minutes to convert 1tonne of waste into 390 kg of biochar and 133 liters of pyrolyser oil. After testing, biochar/binder ratios of 27/1.1, 27/2.7 and 27/2.1 for starch, gum arabic and clay, respectively, at a compaction pressure of 7.8 bar were validated.
Synthetic Metals, Mar 1, 2001
An investigation of third-order nonlinear optical characterization of newly synthesized conjugate... more An investigation of third-order nonlinear optical characterization of newly synthesized conjugated benzodioxal derivatives has been done by using nanosecond Z-scan technique at 532 nm. The molecules demonstrate self-defocusing effect with intensity dependent refractive index (n 2) of the order of 10 À 14 cm 2 /W. The measured molecular TPA cross-section is ranging from 2.47 Â 10 À 47 cm 4 s/photon to 6.00 cm 4 s/photon. Their input-output curves indicate that there is a clear optical power limiting behavior with the limiting threshold in the range 125-181 mJ. The main factor to exhibit the observed nonlinearity in these molecules is the presence of charge donor and acceptor groups. The increased conjugation length increases the nonlinear refraction and increased electron density enhances the nonlinear absorption. The molecules exhibit good nonlinear optical properties, comparable to those of regular azoaromatic compounds. Therefore, the molecules investigated here are promising candidates for optical power limiting devices.
<p>Green hydrogen has been identified as a key energy carrier to decarboniz... more <p>Green hydrogen has been identified as a key energy carrier to decarbonize the main emission sectors. In the industry sectors hydrogen can be used as a reducing agent in the metallurgy, in the transportation sector hydrogen can be used as a fuel and in the energy sector hydrogen can be used as an energy storage option. However, the production of hydrogen is energy intensive and can only lead to a reduction of greenhouse gas emissions if the primary energy source is renewable, carbon-free, and has a low ecological footprint. Wind, geothermal, solar and hydropower have been identified as key sources for sustainable and green hydrogen production, especially if excess energy is used for the hydrogen production. Unfortunately, large scale renewable energy production is frequently located at distant location from main consumers. We assess the challenges and opportunities of two remote production hot spots for sustainable and green hydrogen, namely Iceland and northern Africa. We will present different methods, ranging from energy modelling, life cycle assessment, to stakeholder analysis to present a holistic picture of sustainable green hydrogen production. Based on our preliminary results, we conclude that Iceland as well as northern Africa have the potential to produce sustainable and green hydrogen.</p>
Proceedings of SPIE, Feb 6, 2004
A series of novel pi-conjugated polymers containing ruthenium bipyridine complexes have been synt... more A series of novel pi-conjugated polymers containing ruthenium bipyridine complexes have been synthesized by a cross-coupling reaction and characterized. These polymers exhibit absorption maxima at around 330 - 350 nm (pi-pi*) and 460-500 nm (MLCT) respectively. They are soluble in common organic solvents and all polymers can be converted into transparent films. We investigated the influence of different donating and acceptor diethynylarenes on the UV/Vis spectra. The oxidation potentials, which have been measured by cyclic- and square-wave voltammetry, show a typical Ru2+/3+ exhibiting at around + 1.26 V vs. SCE and an additional peak for triphenylamine containing polymers (+ 1.07 V C4c). The polymers were further characterized with photoluminescence measurements. When excited at 442 nm (C2), the polymer showed an emission peak at 690 nm. This peak is attributed to the MLCT states.
Polymer, Nov 1, 2014
Abstract A new electroluminescent polymer, poly{9-(2-ethylhexyl)carbazole-2,7-diethynylene- alt -... more Abstract A new electroluminescent polymer, poly{9-(2-ethylhexyl)carbazole-2,7-diethynylene- alt -tris[2,5-bis(2-ethylhexyloxy)-1,4-phenylenevinylene]} ( PCzE - PPV ), is synthesized, and its photophysical and electrochemical properties and electroluminescence (EL) are studied. In solution, an intense photoluminescence (PL) emission with a maximum at about 520 nm is observed. PL decay dynamics in solution are best described by a monoexponential function with a lifetime of 0.76 ns. Thin films exhibit an intense PL emission with a slightly red-shifted maximum at 532 nm compared to that in the solution spectra. The polymer oxidizes and reduces quasi-reversibly. The ionization potential (HOMO level) of 5.3 eV and the electron affinity (LUMO level) of 2.80 eV are evaluated from cyclovoltammetric measurements. The electrochemical bandgap value (2.45 eV) is in good agreement with the optical bandgap value. Using new polymer, light-emitting devices (LEDs) with a luminance higher than 3000 cd m −2 and low onset voltages at about 3 V are fabricated. The shape of EL spectra of the LEDs is similar to that of PL spectra of the thin films.
Designed Monomers and Polymers, 2000
Novel 2,2′-bipyridine-based conjugated polymers of formula 2 have been synthesized by Pd-catalyze... more Novel 2,2′-bipyridine-based conjugated polymers of formula 2 have been synthesized by Pd-catalyzed cross-coupling reactions between 4,4′-dibromo-2,2′-bipyridine (3) and substituted phenyldiacetylenes (4). The zig-zag arrangement of the 2,2′-bipyridine units implies a helical conformation of 2. The solubility of 2 requires at least a dodecyl side-chain. 2 is thermostable up to 400°C. The polymers have a high fluorescence quantum yield in solution (60%).
Advanced Energy Materials, Jun 15, 2012
Advanced Science, Dec 1, 2016
Source Measure Unit. For PL normalization and evaluation of optical band-gap, thin film transmiss... more Source Measure Unit. For PL normalization and evaluation of optical band-gap, thin film transmission, and reflection spectra were recorded with a Varian Cary 5000 spectrophotometer under VW condition [87] and reassembled to the thin film absorption spectra. For reference, all photovoltaic parameters on this set of devices have been published in ref. [33]. C. Kästner is grateful to the Thüringer Landesgraduiertenschule für Photovoltaik "PhotoGrad" for financial support. D. A. M. Egbe and H. Hoppe are grateful for financial support by the Deutsche Forschungsgemeinschaft (DFG) and the Austrian Science Fund (FWF) (Contract No. I1703-N20) in the framework of D.A.CH project "PhotogenOrder." Furthermore, the authors gratefully acknowledge valuable scientific discussions with Dr.
Journal of Polymer Science Part A, Jun 19, 2002
Luminophoric dialdehyde 1,4-bis[4-formylphenylethynyl-(2,5-dioctadecyloxyphenyl)-buta-1,3-diyne] ... more Luminophoric dialdehyde 1,4-bis[4-formylphenylethynyl-(2,5-dioctadecyloxyphenyl)-buta-1,3-diyne] (4) enables the synthesis of diyne-containing hybrid polyphenyleneethynylene/poly(p-phenylenevinylene) polymer poly[1,4-phenylene-ethynylene-1,4-(2,5-dioctadecyloxy)phenylene-butadi-1,3-ynylene-1,4-(2,5-dioctadecyloxy)phenylene-ethynylene-1,4-phenylene-ethene-1,2-diyl-1,4-(2,5-dioctadecyloxy)phenylene-ethene-1,2-diyl] (7) with a well-defined general structure (-Ph-C≡C-Ar-C≡C-C≡C-Ar-C≡C-Ph-CH=CH-Ar-CH=CH-) n , which was confirmed by NMR and infrared spectroscopy. The highly luminescent material is thermostable, soluble in usual organic solvents through the grafting of octadecyloxy side groups, and can be processed into transparent films. With the aim to investigate the effect of -C≡C-C≡C-in the photophysical behavior of 7, a comparison of the photophysics of monomers 3 [1,4-bis(4-formylphenylethynyl)-2,5-dioctadecyloxybenzene] and 4 and subsequently of their respective polymers 6 and 7 has been carried out. Similar photophysical behaviors for 6 (poly[1,4-phenylenethynylene-1,4-(2,5-dioctadecyloxyphenylene)ethene-1,2-diyl]) and 7 were observed in dilute CHCl 3 solution as a result of an identical chromophore system responsible for the absorption (λ a = 448 nm) and emission (λ f = 490 nm) in both compounds. The increased planarization and enhanced rigidity of the conjugated backbone in the solid state at room temperature as well as in frozen dilute tetrahydrofuran solution at 77 K cause the bathochromic shift of the absorption and emission spectra. The large octadecyloxy side chains obviously limit strong π-π interchain interactions in the solid films, which explains the high fluorescence quantum yields of 35 and 52% obtained for 6 and 7, respectively. The energetically arduous migration of the π electron through the diyne units not only requires a higher threshold voltage for the detection of photoconductivity in 7 but could possibly limit radiationless deactivation channels of the exciton, which explains the approximate 20% fluorescence quantum yields difference between 6 and 7 in the solid state. The electron-withdrawing effect of the triple bonds confer both 6 and 7 with a good electron-accepting property (E ox = 1.39 V vs Ag/AgCl) if used in light-emitting diode devices.
Macromolecules, Nov 1, 2004
ABSTRACT
Energies, Feb 23, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Vacuum, Dec 1, 2015
Organic bulk heterojunction and inverted type solar cells were fabricated using AnE-PVstat:PCBM b... more Organic bulk heterojunction and inverted type solar cells were fabricated using AnE-PVstat:PCBM blends as photoactive layers. The device was inverted using thin films of TiO 2 as hole blocking and electron conducting layers. The power conversion efficiency (PCE) of organic bulk heterojunction solar cells increased from 1.70% to 2.59% when inverted device configuration was used instead of regular organic bulk heterojunction solar cell configuration. Stability studies reveal that the inverted type devices are more stable than the herein investigated regular organic bulk heterojunction solar cells fabricated using AnE-PVstat:PCBM blends as photoactive layers.
Journal of optics, Jul 7, 2004
... J. Opt. A: Pure Appl. Opt. 6 (2004) 791–797 PII: S1464-4258(04)80199-5 Third-order nonlinear ... more ... J. Opt. A: Pure Appl. Opt. 6 (2004) 791–797 PII: S1464-4258(04)80199-5 Third-order nonlinear optical behaviour of hybrid phenylene–ethynylene/ phenylene–vinylene polymersDaniel Ayuk Mbi Egbe1,3, Regina Stockmann1 and Mario Hotzel2,3 ...
Journal of Physical Organic Chemistry, Feb 1, 2000
Alternating oligomers and polymers consisting of 2,2′-bipyridine and diethinylenebenzene units an... more Alternating oligomers and polymers consisting of 2,2′-bipyridine and diethinylenebenzene units and corresponding model compounds were synthesized and investigated in dilute solutions by absorption spectroscopy and by stationary and time-resolved emission spectroscopy. The strictly linear (rod-like) π-chain oligomers/polymers were compared with the angularly linked oligomers/polymers and with related model compounds. The model compounds which already show the essential spectroscopic properties of the oligomers/polymers consist of three (hetero)aromatics linearly connected by two diethenylene groups. These models exhibit fluorescence quantum yields close to unity and short fluorescence decay times around 1 ns. Fluorescence anisotropy and rotational relaxation times are consistent with the Stokes–Einstein equation and the Perrin equation. The absorption and emission spectra of the polymers and their radiative rate constants determined by fluorescence quantum yield and lifetime and according to the Strickler/Berg equation show a conjugation length of one to two repetition units. The conjugation along the chain is stronger in linear than in angular polymers and stronger in alkoxy-substituted than in unsubstituted polymers. In angular polymers at least two different emitting segments were found. The shortened mean lifetimes and the reduced fluorescence quantum yields and anisotropies of the oligomers/polymers indicate an additional radiationless deactivation channel which is opened by energy migration along the chain. Rates of energy transfer calculated for linear and angular polymers correlate with rates of radiationless deactivation. Copyright © 2000 John Wiley & Sons, Ltd.
Progress in Polymer Science, Oct 1, 2009
Poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s (PAE–PAVs) are a new class of conjugated com... more Poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s (PAE–PAVs) are a new class of conjugated compounds combining the intrinsic properties of both poly(arylene-ethynylene) (PAE) and poly(arylene-vinylene) (PAV) into a single polymeric backbone with additional structure-specific properties. On the one hand, they exhibit red-shifted absorption and emission spectra as well as an enhanced solid state photoluminescence quantum yield as compared to PAEs and, on the other hand, they
Macromolecular Chemistry and Physics, Sep 1, 2001
The polycondensation reactions of luminophoric dialdehydes 5 and bisphosphonates 3 provide a new ... more The polycondensation reactions of luminophoric dialdehydes 5 and bisphosphonates 3 provide a new type of π-conjugated polymers 7 with well-defined structure (—Ar—C≡C—Ar—C≡C—Ar—CH=CH—Ar— CH=CH—)n , which was confirmed by NMR, infrared and UV-Vis spectroscopy. High molecular weight (Mw up to 500 000 g/mol), thermostable, soluble and transparent film-forming materials were obtained. The grafting of large alkoxy side chains enhances the solubility and processability of the new compounds. The incorporation of triple bonds into the PPV backbone increases the oxidation and reduction potentials, thus making these polymers potentially good electron-transporting materials if used in light-emissive-diode devices. The polymers are photoconductive and show very good photoluminescent properties in solution as well as in the solid state. Identical absorption (λmax,abs = 445 nm) and emission (λmax,em = 490 nm) behaviors were observed for all polymers in solution (CHCl3), resulting in a fluorescence quantum yield of 70%, but the photophysical behavior in solid state was side group dependent. Polymer 7ac shows a very large Stokes shift (137 nm) and lower fluorescence quantum yield (19%), whereas 7aa, 7bb and 7ab, consisting of side groups equal to or longer than O(CH2)11CH3 are characterized by smaller Stokes shifts (around 30 nm) and comparatively higher fluorescence quantum yields (34 to 44%).
Macromolecular Chemistry and Physics, Oct 18, 2004
Back Cover: The Cover shows the absorption and emission spectra of alkyl-and alkoxysubstituted di... more Back Cover: The Cover shows the absorption and emission spectra of alkyl-and alkoxysubstituted dialdehydes, and their respective poly[(phenylene ethynylene)-alt-(phenylene vinylene)] hybrid polymers, obtained by the polycondensation of the dialdehydes with alkoxy-substituted bisphosphonates. Photophysical investigations and quantum chemical calculations reveal remarkable differences between alkyl-and alkoxy-substituted dialdehydes. On the contrary, their polymers exhibit similar photophysical properties, indicating an identical fluorophore system located around the lower energy phenylene-vinylene segment of the polymers. Further details can be found in the Full Paper by D. A. M. Egbe,* S. Sell, C. Ulbricht, E. Birckner, and U.-W. Grummt on page 2105.
Synthetic Metals, May 1, 2023
The design of advanced new generation conjugated materials with improved properties for photovolt... more The design of advanced new generation conjugated materials with improved properties for photovoltaic applications has been the focus of research in recent years. This work reports on novel anthanthrone/anthracene and anthanthrene/anthracene co-polymers as p-type conjugated semiconductors in organic photovoltaics. The presence of anthracene component with the grafted alkyloxy chains enhanced the solubility and process-ability of the co-polymers. The photophysical and photovoltaic parameters greatly depend on ratio of components of the co-polymers and nature of the grafted chains. Devices using the blends of SV15 and PCBM in 1:2 ratio gave JmathrmsmathrmcJ_{\mathrm{s}\mathrm{c}}Jmathrmsmathrmc 3.97 mA/cm2 and higb VocV_{oc}Voc 0.92 V with efficiency 1.7%.
Wood fuel is undoubtedly the main source of energy for cooking in sub-Saharan Africa as it repres... more Wood fuel is undoubtedly the main source of energy for cooking in sub-Saharan Africa as it represents more than three quarter of household energy consumption. The exploitation of wood for fuel purposes contributes to forest degradation. It is becoming urgent to diversify domestic energy sources. Substituting other forms of energy with traditional ones is extremely difficult due to low income of the population and culinary habits. In this context, ecological charcoal seems to be an attractive alternative to wood energy. Agricultural waste was collected, dried to a moisture content of less than 10%. Waste was pyrolysed and the resulting carbonaceous material mixed with a binder and extruded to form briquettes. Three binders were tested: starch, clay and arabic gum. The pyrolysis of biomass generated three byproducts: a solid (biochar), liquid and gaseous product. This process took 3 hours 45 minutes to convert 1tonne of waste into 390 kg of biochar and 133 liters of pyrolyser oil. After testing, biochar/binder ratios of 27/1.1, 27/2.7 and 27/2.1 for starch, gum arabic and clay, respectively, at a compaction pressure of 7.8 bar were validated.
Synthetic Metals, Mar 1, 2001
An investigation of third-order nonlinear optical characterization of newly synthesized conjugate... more An investigation of third-order nonlinear optical characterization of newly synthesized conjugated benzodioxal derivatives has been done by using nanosecond Z-scan technique at 532 nm. The molecules demonstrate self-defocusing effect with intensity dependent refractive index (n 2) of the order of 10 À 14 cm 2 /W. The measured molecular TPA cross-section is ranging from 2.47 Â 10 À 47 cm 4 s/photon to 6.00 cm 4 s/photon. Their input-output curves indicate that there is a clear optical power limiting behavior with the limiting threshold in the range 125-181 mJ. The main factor to exhibit the observed nonlinearity in these molecules is the presence of charge donor and acceptor groups. The increased conjugation length increases the nonlinear refraction and increased electron density enhances the nonlinear absorption. The molecules exhibit good nonlinear optical properties, comparable to those of regular azoaromatic compounds. Therefore, the molecules investigated here are promising candidates for optical power limiting devices.
<p>Green hydrogen has been identified as a key energy carrier to decarboniz... more <p>Green hydrogen has been identified as a key energy carrier to decarbonize the main emission sectors. In the industry sectors hydrogen can be used as a reducing agent in the metallurgy, in the transportation sector hydrogen can be used as a fuel and in the energy sector hydrogen can be used as an energy storage option. However, the production of hydrogen is energy intensive and can only lead to a reduction of greenhouse gas emissions if the primary energy source is renewable, carbon-free, and has a low ecological footprint. Wind, geothermal, solar and hydropower have been identified as key sources for sustainable and green hydrogen production, especially if excess energy is used for the hydrogen production. Unfortunately, large scale renewable energy production is frequently located at distant location from main consumers. We assess the challenges and opportunities of two remote production hot spots for sustainable and green hydrogen, namely Iceland and northern Africa. We will present different methods, ranging from energy modelling, life cycle assessment, to stakeholder analysis to present a holistic picture of sustainable green hydrogen production. Based on our preliminary results, we conclude that Iceland as well as northern Africa have the potential to produce sustainable and green hydrogen.</p>
Proceedings of SPIE, Feb 6, 2004
A series of novel pi-conjugated polymers containing ruthenium bipyridine complexes have been synt... more A series of novel pi-conjugated polymers containing ruthenium bipyridine complexes have been synthesized by a cross-coupling reaction and characterized. These polymers exhibit absorption maxima at around 330 - 350 nm (pi-pi*) and 460-500 nm (MLCT) respectively. They are soluble in common organic solvents and all polymers can be converted into transparent films. We investigated the influence of different donating and acceptor diethynylarenes on the UV/Vis spectra. The oxidation potentials, which have been measured by cyclic- and square-wave voltammetry, show a typical Ru2+/3+ exhibiting at around + 1.26 V vs. SCE and an additional peak for triphenylamine containing polymers (+ 1.07 V C4c). The polymers were further characterized with photoluminescence measurements. When excited at 442 nm (C2), the polymer showed an emission peak at 690 nm. This peak is attributed to the MLCT states.
Polymer, Nov 1, 2014
Abstract A new electroluminescent polymer, poly{9-(2-ethylhexyl)carbazole-2,7-diethynylene- alt -... more Abstract A new electroluminescent polymer, poly{9-(2-ethylhexyl)carbazole-2,7-diethynylene- alt -tris[2,5-bis(2-ethylhexyloxy)-1,4-phenylenevinylene]} ( PCzE - PPV ), is synthesized, and its photophysical and electrochemical properties and electroluminescence (EL) are studied. In solution, an intense photoluminescence (PL) emission with a maximum at about 520 nm is observed. PL decay dynamics in solution are best described by a monoexponential function with a lifetime of 0.76 ns. Thin films exhibit an intense PL emission with a slightly red-shifted maximum at 532 nm compared to that in the solution spectra. The polymer oxidizes and reduces quasi-reversibly. The ionization potential (HOMO level) of 5.3 eV and the electron affinity (LUMO level) of 2.80 eV are evaluated from cyclovoltammetric measurements. The electrochemical bandgap value (2.45 eV) is in good agreement with the optical bandgap value. Using new polymer, light-emitting devices (LEDs) with a luminance higher than 3000 cd m −2 and low onset voltages at about 3 V are fabricated. The shape of EL spectra of the LEDs is similar to that of PL spectra of the thin films.
Designed Monomers and Polymers, 2000
Novel 2,2′-bipyridine-based conjugated polymers of formula 2 have been synthesized by Pd-catalyze... more Novel 2,2′-bipyridine-based conjugated polymers of formula 2 have been synthesized by Pd-catalyzed cross-coupling reactions between 4,4′-dibromo-2,2′-bipyridine (3) and substituted phenyldiacetylenes (4). The zig-zag arrangement of the 2,2′-bipyridine units implies a helical conformation of 2. The solubility of 2 requires at least a dodecyl side-chain. 2 is thermostable up to 400°C. The polymers have a high fluorescence quantum yield in solution (60%).
Advanced Energy Materials, Jun 15, 2012
Advanced Science, Dec 1, 2016
Source Measure Unit. For PL normalization and evaluation of optical band-gap, thin film transmiss... more Source Measure Unit. For PL normalization and evaluation of optical band-gap, thin film transmission, and reflection spectra were recorded with a Varian Cary 5000 spectrophotometer under VW condition [87] and reassembled to the thin film absorption spectra. For reference, all photovoltaic parameters on this set of devices have been published in ref. [33]. C. Kästner is grateful to the Thüringer Landesgraduiertenschule für Photovoltaik "PhotoGrad" for financial support. D. A. M. Egbe and H. Hoppe are grateful for financial support by the Deutsche Forschungsgemeinschaft (DFG) and the Austrian Science Fund (FWF) (Contract No. I1703-N20) in the framework of D.A.CH project "PhotogenOrder." Furthermore, the authors gratefully acknowledge valuable scientific discussions with Dr.
Journal of Polymer Science Part A, Jun 19, 2002
Luminophoric dialdehyde 1,4-bis[4-formylphenylethynyl-(2,5-dioctadecyloxyphenyl)-buta-1,3-diyne] ... more Luminophoric dialdehyde 1,4-bis[4-formylphenylethynyl-(2,5-dioctadecyloxyphenyl)-buta-1,3-diyne] (4) enables the synthesis of diyne-containing hybrid polyphenyleneethynylene/poly(p-phenylenevinylene) polymer poly[1,4-phenylene-ethynylene-1,4-(2,5-dioctadecyloxy)phenylene-butadi-1,3-ynylene-1,4-(2,5-dioctadecyloxy)phenylene-ethynylene-1,4-phenylene-ethene-1,2-diyl-1,4-(2,5-dioctadecyloxy)phenylene-ethene-1,2-diyl] (7) with a well-defined general structure (-Ph-C≡C-Ar-C≡C-C≡C-Ar-C≡C-Ph-CH=CH-Ar-CH=CH-) n , which was confirmed by NMR and infrared spectroscopy. The highly luminescent material is thermostable, soluble in usual organic solvents through the grafting of octadecyloxy side groups, and can be processed into transparent films. With the aim to investigate the effect of -C≡C-C≡C-in the photophysical behavior of 7, a comparison of the photophysics of monomers 3 [1,4-bis(4-formylphenylethynyl)-2,5-dioctadecyloxybenzene] and 4 and subsequently of their respective polymers 6 and 7 has been carried out. Similar photophysical behaviors for 6 (poly[1,4-phenylenethynylene-1,4-(2,5-dioctadecyloxyphenylene)ethene-1,2-diyl]) and 7 were observed in dilute CHCl 3 solution as a result of an identical chromophore system responsible for the absorption (λ a = 448 nm) and emission (λ f = 490 nm) in both compounds. The increased planarization and enhanced rigidity of the conjugated backbone in the solid state at room temperature as well as in frozen dilute tetrahydrofuran solution at 77 K cause the bathochromic shift of the absorption and emission spectra. The large octadecyloxy side chains obviously limit strong π-π interchain interactions in the solid films, which explains the high fluorescence quantum yields of 35 and 52% obtained for 6 and 7, respectively. The energetically arduous migration of the π electron through the diyne units not only requires a higher threshold voltage for the detection of photoconductivity in 7 but could possibly limit radiationless deactivation channels of the exciton, which explains the approximate 20% fluorescence quantum yields difference between 6 and 7 in the solid state. The electron-withdrawing effect of the triple bonds confer both 6 and 7 with a good electron-accepting property (E ox = 1.39 V vs Ag/AgCl) if used in light-emitting diode devices.
Macromolecules, Nov 1, 2004
ABSTRACT
Energies, Feb 23, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
Vacuum, Dec 1, 2015
Organic bulk heterojunction and inverted type solar cells were fabricated using AnE-PVstat:PCBM b... more Organic bulk heterojunction and inverted type solar cells were fabricated using AnE-PVstat:PCBM blends as photoactive layers. The device was inverted using thin films of TiO 2 as hole blocking and electron conducting layers. The power conversion efficiency (PCE) of organic bulk heterojunction solar cells increased from 1.70% to 2.59% when inverted device configuration was used instead of regular organic bulk heterojunction solar cell configuration. Stability studies reveal that the inverted type devices are more stable than the herein investigated regular organic bulk heterojunction solar cells fabricated using AnE-PVstat:PCBM blends as photoactive layers.
Journal of optics, Jul 7, 2004
... J. Opt. A: Pure Appl. Opt. 6 (2004) 791–797 PII: S1464-4258(04)80199-5 Third-order nonlinear ... more ... J. Opt. A: Pure Appl. Opt. 6 (2004) 791–797 PII: S1464-4258(04)80199-5 Third-order nonlinear optical behaviour of hybrid phenylene–ethynylene/ phenylene–vinylene polymersDaniel Ayuk Mbi Egbe1,3, Regina Stockmann1 and Mario Hotzel2,3 ...
Journal of Physical Organic Chemistry, Feb 1, 2000
Alternating oligomers and polymers consisting of 2,2′-bipyridine and diethinylenebenzene units an... more Alternating oligomers and polymers consisting of 2,2′-bipyridine and diethinylenebenzene units and corresponding model compounds were synthesized and investigated in dilute solutions by absorption spectroscopy and by stationary and time-resolved emission spectroscopy. The strictly linear (rod-like) π-chain oligomers/polymers were compared with the angularly linked oligomers/polymers and with related model compounds. The model compounds which already show the essential spectroscopic properties of the oligomers/polymers consist of three (hetero)aromatics linearly connected by two diethenylene groups. These models exhibit fluorescence quantum yields close to unity and short fluorescence decay times around 1 ns. Fluorescence anisotropy and rotational relaxation times are consistent with the Stokes–Einstein equation and the Perrin equation. The absorption and emission spectra of the polymers and their radiative rate constants determined by fluorescence quantum yield and lifetime and according to the Strickler/Berg equation show a conjugation length of one to two repetition units. The conjugation along the chain is stronger in linear than in angular polymers and stronger in alkoxy-substituted than in unsubstituted polymers. In angular polymers at least two different emitting segments were found. The shortened mean lifetimes and the reduced fluorescence quantum yields and anisotropies of the oligomers/polymers indicate an additional radiationless deactivation channel which is opened by energy migration along the chain. Rates of energy transfer calculated for linear and angular polymers correlate with rates of radiationless deactivation. Copyright © 2000 John Wiley & Sons, Ltd.
Progress in Polymer Science, Oct 1, 2009
Poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s (PAE–PAVs) are a new class of conjugated com... more Poly(arylene-ethynylene)-alt-poly(arylene-vinylene)s (PAE–PAVs) are a new class of conjugated compounds combining the intrinsic properties of both poly(arylene-ethynylene) (PAE) and poly(arylene-vinylene) (PAV) into a single polymeric backbone with additional structure-specific properties. On the one hand, they exhibit red-shifted absorption and emission spectra as well as an enhanced solid state photoluminescence quantum yield as compared to PAEs and, on the other hand, they
Macromolecular Chemistry and Physics, Sep 1, 2001
The polycondensation reactions of luminophoric dialdehydes 5 and bisphosphonates 3 provide a new ... more The polycondensation reactions of luminophoric dialdehydes 5 and bisphosphonates 3 provide a new type of π-conjugated polymers 7 with well-defined structure (—Ar—C≡C—Ar—C≡C—Ar—CH=CH—Ar— CH=CH—)n , which was confirmed by NMR, infrared and UV-Vis spectroscopy. High molecular weight (Mw up to 500 000 g/mol), thermostable, soluble and transparent film-forming materials were obtained. The grafting of large alkoxy side chains enhances the solubility and processability of the new compounds. The incorporation of triple bonds into the PPV backbone increases the oxidation and reduction potentials, thus making these polymers potentially good electron-transporting materials if used in light-emissive-diode devices. The polymers are photoconductive and show very good photoluminescent properties in solution as well as in the solid state. Identical absorption (λmax,abs = 445 nm) and emission (λmax,em = 490 nm) behaviors were observed for all polymers in solution (CHCl3), resulting in a fluorescence quantum yield of 70%, but the photophysical behavior in solid state was side group dependent. Polymer 7ac shows a very large Stokes shift (137 nm) and lower fluorescence quantum yield (19%), whereas 7aa, 7bb and 7ab, consisting of side groups equal to or longer than O(CH2)11CH3 are characterized by smaller Stokes shifts (around 30 nm) and comparatively higher fluorescence quantum yields (34 to 44%).
Macromolecular Chemistry and Physics, Oct 18, 2004
Back Cover: The Cover shows the absorption and emission spectra of alkyl-and alkoxysubstituted di... more Back Cover: The Cover shows the absorption and emission spectra of alkyl-and alkoxysubstituted dialdehydes, and their respective poly[(phenylene ethynylene)-alt-(phenylene vinylene)] hybrid polymers, obtained by the polycondensation of the dialdehydes with alkoxy-substituted bisphosphonates. Photophysical investigations and quantum chemical calculations reveal remarkable differences between alkyl-and alkoxy-substituted dialdehydes. On the contrary, their polymers exhibit similar photophysical properties, indicating an identical fluorophore system located around the lower energy phenylene-vinylene segment of the polymers. Further details can be found in the Full Paper by D. A. M. Egbe,* S. Sell, C. Ulbricht, E. Birckner, and U.-W. Grummt on page 2105.
Synthetic Metals, May 1, 2023
The design of advanced new generation conjugated materials with improved properties for photovolt... more The design of advanced new generation conjugated materials with improved properties for photovoltaic applications has been the focus of research in recent years. This work reports on novel anthanthrone/anthracene and anthanthrene/anthracene co-polymers as p-type conjugated semiconductors in organic photovoltaics. The presence of anthracene component with the grafted alkyloxy chains enhanced the solubility and process-ability of the co-polymers. The photophysical and photovoltaic parameters greatly depend on ratio of components of the co-polymers and nature of the grafted chains. Devices using the blends of SV15 and PCBM in 1:2 ratio gave JmathrmsmathrmcJ_{\mathrm{s}\mathrm{c}}Jmathrmsmathrmc 3.97 mA/cm2 and higb VocV_{oc}Voc 0.92 V with efficiency 1.7%.