scholarly journals Contrasting Photo-Switching Rates in Azobenzene Derivatives: How the Nature of the Substituent Plays a Role

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1019
Author(s):  
Domenico Pirone ◽  
Nuno A. G. Bandeira ◽  
Bartosz Tylkowski ◽  
Emily Boswell ◽  
Regine Labeque ◽  
...  
Keyword(s):  
Visible Light ◽  
Smart Materials ◽  
Density Functional ◽  
Molecular Design ◽  
Visible Region ◽  
Building Blocks ◽  
Stimuli Responsive ◽  
Order Of Magnitude ◽  
Azo Derivatives ◽  
Commercial Polymers

A molecular design approach was used to create asymmetrical visible light-triggered azo-derivatives that can be good candidates for polymer functionalization. The specific electron–donor substituted molecules were characterized and studied by means of NMR analyses and UV-visible spectroscopy, comparing the results with Time Dependent Density Functional (TD-DFT) calculations. A slow rate of isomerization (ki = 1.5 × 10−4 s−1) was discovered for 4-((2-hydroxy-5methylphenyl) diazenyl)-3-methoxybenzoic acid (AZO1). By methylating this moiety, it was possible to unlock the isomerization mechanism for the second molecule, methyl 3-methoxy-4-((2-methoxy-5-methylphenyl) diazenyl)benzoate (AZO2), reaching promising isomerization rates with visible light irradiation in different solvents. It was discovered that this rate was heightened by one order of magnitude (ki = 3.1 × 10−3 s−1) for AZO2. A computational analysis using density functional (DFT/PBE0) and wavefunction (QD-NEVPT2) methodologies provided insight into the photodynamics of these systems. Both molecules require excitation to the second (S2) excited state situated in the visible region to initiate the isomerization. Two classic mechanisms were considered, namely rotation and inversion, with the former being energetically more favorable. These azo-derivatives show potential that paves the way for future applications as building blocks of functional polymers. Likewise, they could be really effective for the modification of existing commercial polymers, thus transferring their stimuli responsive properties to polymeric bulky structures, converting them into smart materials.

scholarly journals C-, N-, S-, and F-Doped Anatase TiO2 (101) with Oxygen Vacancies: Photocatalysts Active in the Visible Region

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Julio César González-Torres ◽  
Enrique Poulain ◽  
Víctor Domínguez-Soria ◽  
Raúl García-Cruz ◽  
Oscar Olvera-Neria
Keyword(s):  
Visible Light ◽  
Conduction Band ◽  
Density Functional ◽  
Oxygen Vacancies ◽  
Visible Region ◽  
Charge Carriers ◽  
Localized States ◽  
Similar Process ◽  
Visible Radiation ◽  
C Doping

Anatase TiO2 presents a large bandgap of 3.2 eV, which inhibits the use of visible light radiation (λ > 387 nm) for generating charge carriers. We studied the activation of TiO2 (101) anatase with visible light by doping with C, N, S, and F atoms. For this purpose, density functional theory and the Hubbard U approach are used. We identify two ways for activating the TiO2 with visible light. The first mechanism is broadening the valence or conduction band; for example, in the S-doped TiO2 (101) system, the valence band is broadened. A similar process can occur in the conduction band when the undercoordinated Ti atoms are exposed on the TiO2 (101) surface. The second mechanism, and more efficient for activating the anatase, is to generate localized states in the gap: N-doping creates localized empty states in the bandgap. For C-doping, the surface TiO2 (101) presents a “cleaner” gap than the bulk TiO2, resulting in fewer recombination centers. The dopant valence electrons determine the number and position of the localized states in the bandgap. The formation of charge carriers with visible light is highly favored by the oxygen vacancies on TiO2 (101). The catalytic activity of C-doping using visible radiation can be explained by its high absorption intensity generated by oxygen vacancies on the surface. The intensity of the visible absorption spectrum of doped TiO2 (101) follows the order: C > N > F > S dopant.

scholarly journals Photoresponse of Visible Light Active CM-n-TiO2, HM-n-TiO2, CM-n-Fe2O3, and CM-p-WO3towards Water Splitting Reaction

2012 ◽  
Vol 2012 ◽  
pp. 1-20 ◽  
Author(s):  
Yasser A. Shaban ◽  
Shahed U. M. Khan
Keyword(s):  
Visible Light ◽  
Titanium Oxide ◽  
Water Splitting ◽  
Monochromatic Light ◽  
Visible Region ◽  
Xenon Lamp ◽  
Light Illumination ◽  
X Ray ◽  
Visible Light Active ◽  
Order Of Magnitude

Photoresponses of visible light active carbon modified titanium oxide (CM-n-TiO2), hydrogen modified titanium oxide (HM-n-TiO2), carbon modified iron oxide (CM-n-Fe2O3), carbon modified tungsten oxide (CM-p-WO3) towards water splitting reaction are reported in this article. Carbon and hydrogen in titanium oxide were found to be responsible for red shift from UV region to visible region which in turn enhanced the photoconversion efficiency by an order of magnitude for water splitting reaction. Photocurrent densities and photoconversion efficiencies of regular n-TiO2and CM-n-TiO2towards water splitting reaction under monochromatic light illumination from a xenon lamp and sunlight were compared and found in reasonable agreement. These oxides were characterized by photocurrent measurements,UV-Visspectra, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) studies and these results are also reported in this article.

ELECTRONIC STRUCTURES OF S-DOPED ANATASE AND RUTILE TiO2

2007 ◽  
Vol 06 (01) ◽  
pp. 23-32 ◽  
Author(s):  
XIN-GUO MA ◽  
CHAO-QUN TANG ◽  
XIAO-HUA YANG
Keyword(s):  
Photocatalytic Activity ◽  
Visible Light ◽  
Valence Band ◽  
Visible Light Irradiation ◽  
Electronic Structures ◽  
Density Functional ◽  
Visible Region ◽  
Light Irradiation ◽  
Band Shift ◽  
Deep Impurity

The electronic structures of S -doped TiO 2 have been carried out by first-principles calculations based on density functional theory with plane-wave ultrasoft pseudopotential method. Comparing anion doping with cation doping in anatase and rutile, we found different energy band structures and origins of photoactivity of S -doped TiO 2. For anion-doped TiO 2, new S –3p bands appear and which lie slightly above the top of the O –2p valence band. It plays a significant role in increasing absorbance in the visible region, resulting in improvement in photocatalytic activity under visible-light irradiation. For cation-doped TiO 2, the potential of the O –2p valence band shift much downwards, yielding the stronger oxidative power than that of undoped and S anion-doped TiO 2. Nevertheless, the deep impurity states in BG (bond gap) that originate from the S -dopant have negative effects on the recombination of the photoexcited electrons and holes. From our calculated results, we can explain their differences in photocatalytic activity under visible-light irradiation.

scholarly journals MOLECULAR SWITCH BASED ON BITHIOPHENE-AZOBENZENE: HOW TO CONTROL CONDUCTANCE THROUGH THE MONOLAYER USING LIGHT

2021 ◽  
pp. 7-20
Author(s):  
Владислав Анатольевич Савченко ◽  
Ольга Александровна Гуськова
Keyword(s):  
Density Functional ◽  
Rational Design ◽  
Molecular Design ◽  
Uv Light ◽  
Light Stimulus ◽  
Gold Cluster ◽  
Stimuli Responsive ◽  
Anchor Group ◽  
Light Stimuli ◽  
Conductance Ratio

Молекулярные переключатели на основе азобензола (азо) являются светочувствительными молекулами, которые могут переключаться между двумя конфигурационными состояниями под действием света. Светочувствительные азо -монослои можно использовать для модуляции работы выхода, то есть они влияют на свойства электродов. В данной работе мы отвечаем на вопрос, что происходит со структурами, электронными свойствами и перераспределением заряда в монослоях азобитиофена (азо-бт) в зависимости от светового стимула, используя теорию функционала плотности. Моделируются два типа переключателей, различающихся расположением азо и бт от группы пришивки молекулы к поверхности: азо-бт и бт-азо . Один из них (бт-азо) описан в литературе, другой же является продуктом молекулярного дизайна. Мы описываем транс- и цис-изомеры для каждого переключателя, находящегося в контакте с кластером золота. Наше моделирование объясняет гигантское соотношение в проводимости ON/OFF-состояний при воздействии УФ-излучения на монослой улучшенной электронной связью между цис-изомерами (состояние ON) и кластером золота. Транс-изомеры же (OFF состояние) моделируемых переключателей играют роль изоляторов. Кроме того, мы показываем, какие именно свойства улучшаются после молекулярного дизайна. Данное исследование открывает новые возможности в разработке инновационных модификаций поверхности электродов. Molecular switches based on azobenzene (azo) are defined as light-responsive molecules which can change between two configurational states under light stimuli. Responsive azo monolayers can be used to modulate the work function, i.e. they tune the properties of the interfaces at the electrodes. In this work, we investigate what happens to the structures, electronic properties, and the charge redistribution within azo-bithiophene (azo-bt) monolayers depending on the light stimulus using density functional theory. Two types of switches differing in the order of azo and bt counting from the anchor group are modelled: azo-bt and bt-azo . One of them (bt-azo) is known from the literature, the remaining one is a product of rational design. We describe trans- and cis-isomers for each switch being in a contact with a gold cluster. Our simulations explain a giant ON/OFF conductance ratio upon UV light stimulus by improved electronic coupling between the cis-isomers (ON-state) and the gold cluster. The trans-isomers (OFF-state) of the simulated switches play the role of the insulators. Moreover, we show which molecular properties are enchanced by molecular design. This study opens up new avenues to the development of the innovative design of electrode surface modifications.

scholarly journals DFT Study of Se and Te Doped SrTiO 3 for Enhanced Visible-Light Driven Phtocatalytic Hydrogen Production

2021 ◽  
Author(s):  
Hakim BENTOUR ◽  
Mourad Boujnah ◽  
Mohamed Houmad ◽  
Mourad El Yadari ◽  
Abdelilah BENYOUSSEF ◽  
...  
Keyword(s):  
Visible Light ◽  
Band Gap ◽  
Water Splitting ◽  
Density Functional ◽  
Hydrogen Generation ◽  
Visible Region ◽  
Solar Spectrum ◽  
Photogenerated Electron ◽  
Generalized Gradient ◽  
Light Activity

Abstract The pure STiO3 has been experimentally demonstrated to catalyze H2 production using water splitting, but the reaction can only be driven by Ultraviolet (UV) radiation due to the large band gap of SrTiO3. This motivated us to search efficient strategy to tune its band gap, so that it can function in the visible region of the solar spectrum. In this study, the electronic, optical and photocatalytic properties of Se-doped, and Te-doped SrTiO3 has been investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). Our results reveal that the effect of doping can lead to band gap narrowing without introducing any isolated mid-gap states. This improves greatly the visible light activity of SrTiO3 and depresses the recombination of photogenerated electron-hole pairs. Furthermore, the locations of calculated band edges relative to the water reduction and oxidation levels for doped systems meet the water-splitting requirements. Consequently, our results show that the performance of SrTiO3 for hydrogen generation by photocatalytic water splitting is significantly enhanced with Se and Te doping. In particular, Te doping can enhance greatly the visible light photocatalytic activity of SrTiO3. We expect this study can provide a theoretical basis for a prospective experimental works.

scholarly journals Theoretical insights of codoping to modulate electronic structure of $$\hbox {TiO}_2$$ and $$\hbox {SrTiO}_3$$ for enhanced photocatalytic efficiency

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Manish Kumar ◽  
Pooja Basera ◽  
Shikha Saini ◽  
Saswata Bhattacharya
Keyword(s):  
Electronic Structure ◽  
Visible Light ◽  
Band Gap ◽  
Density Functional ◽  
Low Cost ◽  
Visible Region ◽  
Photocatalytic Efficiency ◽  
Large Shift ◽  
Realistic Condition ◽  
Charged Defects

Abstract $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 are well known materials in the field of photocatalysis due to their exceptional electronic structure, high chemical stability, non-toxicity and low cost. However, owing to the wide band gap, these can be utilized only in the UV region. Thus, it’s necessary to expand their optical response in visible region by reducing their band gap through doping with metals, nonmetals or the combination of different elements, while retaining intact the photocatalytic efficiency. We report here, the codoping of a metal and a nonmetal in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 for efficient photocatalytic water splitting using hybrid density functional theory and ab initio atomistic thermodynamics. The latter ensures to capture the environmental effect to understand thermodynamic stability of the charged defects at a realistic condition. We have observed that the charged defects are stable in addition to neutral defects in anatase $$\hbox {TiO}_2$$ TiO 2 and the codopants act as donor as well as acceptor depending on the nature of doping (p-type or n-type). However, the most stable codopants in $$\hbox {SrTiO}_3$$ SrTiO 3 mostly act as donor. Our results reveal that despite the response in visible light region, the codoping in $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 cannot always enhance the photocatalytic activity due to either the formation of recombination centers or the large shift in the conduction band minimum or valence band maximum. Amongst various metal-nonmetal combinations, $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O (i.e. Mn is substituted at Ti site and S is substituted at O site), $$\hbox {S}_\text {O}$$ S O in anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {Mn}_\text {Ti}\hbox {S}_\text {O}$$ Mn Ti S O , $$\hbox {Mn}_\text {Sr}\hbox {N}_\text {O}$$ Mn Sr N O in $$\hbox {SrTiO}_3$$ SrTiO 3 are the most potent candidates to enhance the photocatalytic efficiency of anatase $$\hbox {TiO}_2$$ TiO 2 and $$\hbox {SrTiO}_3$$ SrTiO 3 under visible light irradiation.

scholarly journals Stimuli Responsive Materials Supported by Orthogonal Hydrogen and Halogen Bonding or I···Alkene Interaction

Molecules ◽  
2021 ◽  
Vol 26 (24) ◽  
pp. 7586
Author(s):  
Pierre Frangville ◽  
Shiv Kumar ◽  
Michel Gelbcke ◽  
Kristof Van Van Hecke ◽  
Franck Meyer
Keyword(s):  
Smart Materials ◽  
Color Change ◽  
Uv Light ◽  
Halogen Bond ◽  
Halogen Bonding ◽  
Building Blocks ◽  
Stimuli Responsive ◽  
Compound I ◽  
Ph Variation ◽  
Responsive Materials

Smart materials represent an elegant class of (macro)-molecules endowed with the ability to react to chemical/physical changes in the environment. Herein, we prepared new photo responsive azobenzenes possessing halogen bond donor groups. The X-ray structures of two molecules highlight supramolecular organizations governed by unusual noncovalent bonds. In azo dye I-azo-NO2, the nitro group is engaged in orthogonal H···O···I halogen and hydrogen bonding, linking the units in parallel undulating chains. As far as compound I-azo-NH-MMA is concerned, a non-centrosymmetric pattern is formed due to a very rare I···π interaction involving the alkene group supplemented by hydrogen bonds. The Cambridge Structural Database contains only four structures showing the same I···CH2=C contact. For all compounds, an 19F-NMR spectroscopic analysis confirms the formation of halogen bonds in solution through a recognition process with chloride anion, and the reversible photo-responsiveness is demonstrated upon exposing a solution to UV light irradiation. Finally, the intermediate I–azo–NH2 also shows a pronounced color change due to pH variation. These azobenzenes are thereby attractive building blocks to design future multi-stimuli responsive materials for highly functional devices.

Molecular Design of Organically-Modified ‘Smart’ Sol-Gel Materials

2002 ◽  
Vol 726 ◽  
Author(s):  
Mukti S. Rao ◽  
Bakul C. Dave
Keyword(s):  
Smart Materials ◽  
Structural Changes ◽  
Molecular Design ◽  
Molecular Level ◽  
Sol Gel ◽  
Stimuli Responsive ◽  
Design Synthesis ◽  
Organically Modified Silicates ◽  
Organically Modified ◽  
Responsive Behavior

AbstractThe design, synthesis and stimuli-responsive behavior of organically-modified silicates (ORMOSILS) is reported. The ORMOSILS behave as ‘smart’ materials by undergoing structural changes at the molecular level to respond to changes in environmental variables. Typical responses in the form of swelling/shrinkage with respect to changes in temperature, pH, and salt concentrations are presented. Finally, the nature of predominant mechanism responsible for the sol-gel's behavior towards combined stimuli of high temperature and low pH is discussed.

scholarly journals Computational Exploration of Functionalized Rhombellanes: Building Blocks and Double-Shell Structures

Symmetry ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 343 ◽  
Author(s):  
Katalin Nagy ◽  
Beata Szefler ◽  
Csaba L. Nagy
Keyword(s):  
Density Functional ◽  
Molecular Design ◽  
Drug Carrier ◽  
Geometry Optimization ◽  
Molecular Geometry ◽  
Building Blocks ◽  
Great Promise ◽  
Molecular Symmetry ◽  
Guest Molecules ◽  
Computational Exploration

Double-shell covalent assemblies with the framework of the cube–rhombellane were recently proposed as potential drug delivery systems. Their potential to encapsulate guest molecules combined with appropriate surface modifications show great promise to meet the prerequisites of a drug carrier. This work reports the molecular design of such clusters with high molecular symmetry, as well as the evaluation of the geometric and electronic properties using density functional theory. The computational studies of the double-shell assemblies and their corresponding building blocks were conducted using the B3LYP/6-31G(d,p) method as implemented in Gaussian 09. The results show that the assembly of the building blocks is energetically favorable, leading to clusters with higher stability than the corresponding shell fragments, with large HOMO–LUMO gap values. In case of aromatic systems, interlayer stacking interactions between benzene rings contribute to the molecular geometry and stability. During geometry optimization the clusters preserve the high molecular symmetry of the building blocks.

scholarly journals Investigation of Structural and Optoelectronic Properties of N-Doped Hexagonal Phases of TiO2 (TiO2-xNx) Nanoparticles with DFT Realization: OPTIMIZATION of the Band Gap and Optical Properties for Visible-Light Absorption and Photovoltaic Applications

2021 ◽  
Vol 12 (3) ◽  
pp. 3836-3848
Keyword(s):  
Optical Properties ◽  
Solar Cells ◽  
Visible Light ◽  
Density Functional ◽  
Visible Region ◽  
Absorption Capacity ◽  
Optical Parameters ◽  
Effective Electron ◽  
Doped Tio2 ◽  
Electronic And Optical Properties

The geometric structure, electronic and optical properties of N-doped TiO2 (TiO2-xNx) were studied within the framework of density functional theory. The effective electron-electron exchange-correlation functional and the modified Becke–Johnson potential were used to calculate electronic and optical properties. The calculated optical parameters and the density of electronic states indicate that the TiO2-xNx (0.06 ≤ x ≤ 0.25) system has a property favorable for application in solar cells. The calculated structural characteristics show that the size of these systems increases with the increasing concentration of additives. The electronic properties of N-doped TiO2 show that the bandgaps tend to decrease, and some 2p states of N atoms are located inside the bandgap, which leads to a decrease in the photon energy of the transition and absorption of visible light. As a result, the bandgap effectively decreases with doping concentration increase, while the absorption is effectively improved due to the extended absorption range, both ultraviolet, visible, and infrared range of light emission. It was found that the optimal concentration of nitrogen doping (12.5 at.%) noticeably increases the absorption capacity; hence, the conversion efficiency of TiO2 in the visible region of radiation and effectively reduces the bandgap from 3.2 to 2.4 eV. However, any further increase in concentration does not lead to an additional improvement of the absorption capacity despite the change in the bandgap, which is in good agreement with the existing experimental data. These superior characteristics make N-doped TiO2 a promising material for low-cost, high-efficiency solar cells for the mass market.

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