Dithienylethene optical switches : multicomponent molecular systems

Dithienylethenes are photochromic compounds that interconvert between two distinct states, between colorless open form and colored closed form when irradiation with ultraviolet and visible light, respectively. In this thesis, photochromic dithienylethene switching is employed to investigate multi-functional systems. The synthesis and photochemical characterization of a dithienylethene dimer covalently tethered by a short linker, -SiMe2-, is described as multiswitches for multi-addressable systems. Importantly, it was found that there is no significant intramolecular interaction between the two dithienylethene units despite theirs proximity. Secondly, the photo- and electrochemical properties of self-assembled monolayers of diarylethenes on non-metallic surfaces (quartz and ITO surfaces) are investigated. The state of the modified surface can be read ‘non-destructively’ by electrochemical readout to achieve Read/Write/Erase information storage. Thirdly, the photochemical switching properties of dithienylethene compounds, which can be used to control the electropolymerization properties of bis-terthiophene monomer onto the surface with UV and visible light, respectively, is described. In the open state, electropolymerization yields alkene bridged sexithiophene polymers through oxidative α,α- coupling, while in the closed state the polymerizability is switched off. Moreover, the photoswitchable sexithiophene molecular wires were prepared by employing electrochemical dimerization of dithienylethene monomers. The photochromic dithienylethene units retain their photochemical properties when part of an extended π- conjugated sexithiophene system. Finally, the syntheses of star-shaped dithienylethene substituted hexaphenylbenzenes through a dicobaltoctacarbonyl-catalyzed cyclotrimerization reaction. This reaction represents a direct facile method for the synthesis of hexaphenylbenzene centered multi-dithienylethene systems.

Photochromic Intercalation Compounds

Photochromism of intercalation compounds has been investigated so far. Starting from fundamental studies on the photochromic reactions of the dyes in the presence of layered materials, the precise design of the nanostructures of intercalation compounds toward controlled photochemical reactions and the creation of novel photoresponsive supramolecular systems based on layered solids have been a topic of interests. Various layered materials with different surface chemistries have been used as hosts for the controlled orientation, and aggregation of the intercalated dyes and the states of the intercalated guests affected photoresponses. Molecular design of the photochromic dyes has also been conducted in order to organize them on layered solids with the desired manner. On the other hand, layered solids with such functions as semiconducting and magnetic have been examined to host photochromic dyes for the photoresponsive changes in the materials' properties.ArticlePHOTOFUNCTIONAL LAYERED MATERIALS. 166: 177-211 (2015)journal articl

Multi Stimuli-responsive Organic Salts: From preparation to functional device application

The discovery of novel and efficient stimuli-responsive materials that change their properties according to external stimuli and therefore, adjust to our demands become an interesting research topic for several potential applications. The integration of the most promissory stimuli-responsive materials in devices for antiglare car mirrors, smart windows, sunglasses, sensors, among others has been applied. In this thesis, the development and application of stimuli-responsive materials containing ionic photochromic or electrochromic units have been explored. In general, it is possible to incorporate specific scaffolds possessing pH, temperature, and light or electron-transfer stimuli-responsive behaviour in the cation or anion structures. Also, ionic polymers based on these structures have been investigated. In this context, 4,4’-bipyridinium, diarylethenes and flavylium were selected as electrochromic and photochromic units, respectively. For the preparation of the selected organic salts including polymers, different synthetic routes and purification processes have been followed. Detailed characterization of all prepared salts by spectroscopic techniques in order to elucidate their structures and purities has been performed. Thermal, rheological, photochemical and electrochemical properties of some prepared salts were also studied. It is important to focus that the adequate selection of the counter-ions can be crucial to achieve ionic liquids as well as to tune their final properties. The most promissory electrochromic salts based on 4,4’-bipyridinium symmetrical and non-symmetrical di and tetra-cations as well as ionic polymers were tested in liquid, gel or solid electrochromic devices. The substituents from bipyridinium scaffold as well as counter-ions can significantly influence the electrochromic performance in particular its reversibility; stability; colour contrast and transition times. Photochromic Room Temperature Ionic Liquid based on the combination of diarylethene derivative anion with tri-octyl methylammonium ([ALIQUAT]) cation was developed and characterized. Additionally, a new thermal, pH and photo-stimuli responsive co-polymer containing N-isopropylacrylamide and flavylium derivative have been prepared. The chemical versatility of the prepared ionic photo- and electrochromic materials opens excellent perspectives for future applications as efficient and reversible multi stimuli-responsive materials

Simulation Of Photochromic Compounds Using Density Functional Theory Methods

This Thesis describes the systematic theoretical study aimed at prediction of the essential properties for the functional organic molecules that belong to diarylethene (DA) family of compounds. Diarylethenes present the distinct ability to change color under the influence of light, known as photochromism. This change is due to ultrafast chemical transition from open to closed ring isomers (photocyclization). It can be used for optical data storage, photoswitching, and other photonic applications. In this work we apply Density Functional Theory methods to predict 6 of the related properties: (i) molecular geometry; (ii) resonant wavelength; (iii) thermal stability; (iv) fatigue resistance; (v) quantum yield and (vi) nanoscale organization of the material. In order to study sensitivity at diode laser wavelengths, we optimized geometry and calculated vertical absorption spectra for a benchmark set of 28 diarylethenes. Bond length alternation (BLA) parameters and maximum absorption wavelengths (λmax) are compared to the data presently available from X-ray diffraction and spectroscopy experiments. We conclude that TD-M05/6-31G*/PCM//M05-2X/6-31G*/PCM level of theory gives the best agreement for both the parameters. For our predictions the root mean square deviation (RMSD) are below 0.014 Å for the BLAs and 25 nm for λmax. The polarization functions in the basis set and solvent effects are both important for this agreement. Next we consider thermal stability. Our results suggest that UB3LYP and UM05-2X functionals predict the activation barrier for the cycloreversion reaction within 3-4 kcal/mol from experimental value for a set of 7 photochromic compounds. We also study thermal fatigue, defined as the rate of undesirable photochemical side reactions. In order to predict the kinetics of photochemical fatigue, we investigate the mechanism of by-product formation. It has been established experimentally that the by-product is formed from the closed isomer; however the mechanism was not known. We found that the thermal by-product pathway involves the bicyclohexane (BCH) ring formation as a stable intermediate, while the photochemical by-product formation pathway may involve the methylcyclopentene diradical (MCPD) intermediate. At UM05-2X/6-31G* level, the calculated barrier between the closed form and the BCH intermediate is 51.2 kcal/mol and the barrier between the BCH intermediate and the by-product 16.2 kcal/mol. Next we investigate two theoretical approaches to the prediction of quantum yield (QY) for a set of 14 diarylethene derivatives at the validated M05-2X/6-31G* theory level. These include population of ground-state conformers and location of the pericycylic minimum on the potential energy surface 2-A state. Finally, we investigate the possibility of nanoscale organization of the photochromic material based on DNA template, as an alternative to the amorphous polymer matrix. Here we demonstrate that Molecular Dynamic methods are capable to describe the intercalation of π-conjugated systems between DNA base pairs and accurately reproduced the available photophysical properties of these nanocomposites. In summary, our results are in good agreement with the experimental data for the benchmark set of molecules we conclude that Density Functional Theory methods could be successfully used as an important component of material design strategy in prediction of accurate molecular geometry, absorption spectra, thermal stability of isomers, fatigue resistance, quantum yield of photocyclization and photophysical properties of nanocomposites

The toolbox of porous anodic aluminum oxide–based nanocomposites: from preparation to application

Anodic aluminum oxide (AAO) templates have been intensively investigated during the past decades and have meanwhile been widely applied through both sacrificial and non-sacrificial pathways. In numerous non-sacrificial applications, the AAO membrane is maintained as part of the obtained composite materials; hence, the template structure and topography determine to a great extent the potential applications. Through-hole isotropic AAO features nanochannels that promote transfer of matter, while anisotropic AAO with barrier layer exhibits nanocavities suitable as independent and homogenous containers. By combining the two kinds of AAO membranes with diverse organic and inorganic materials through physical interactions or chemical bonds, AAO composites are designed and applied in versatile fields such as catalysis, drug release platform, separation membrane, optical appliances, sensors, cell culture, energy, and electronic devices. Therefore, within this review, a perspective on exhilarating prospect for complementary advancement on AAO composites both in preparation and application is provided

Photoswitchable peptidomimetics with diarylethene building blocks

Incorporation of molecular photoswitches into peptides or proteins should allow reversible control of their structure and functions by means of photoisomerization. The aim of this study was to explore the practical possibilities of polypeptide modification using photoswitchable diarylethene-based building blocks, and to investigate the effects of the photoinduced isomerization on the structure and function of several biologically active peptides