Photo Switching Research Articles

Recent Applications of Azo Dyes: A Paradigm Shift from Medicinal Chemistry to Biomedical Sciences.

Azo molecules possess the characteristic azo bond (-N=N-) and are considered fascinating motifs in organic chemistry. Since the last century, these brightly colored compounds have been widely employed as dyes across several industries in applications for printing, food, paper, cosmetics, lasers, electronics, optics, material sciences, etc. The discovery of Prontosil, an antibacterial drug, propelled azo compounds into the limelight in the field of medicinal chemistry. Subsequent discoveries including Phenazopyridine, Basalazide, and Sulfasalazine enabled azo compounds to occupy a significant role in the drug market. Furthermore, azo compounds have been employed as antibacterial, antimalarial, antifungal, antioxidant, as well as antiviral agents. The metabolic degradation of many azo dyes can induce liver problems if ingested, posing a safety concern and limiting their application as azo dyes in medicinal chemistry. However, azo dyes remain particularly significant for applications in cancer chemotherapy. Recently, a paradigm shift has been observed in the use of azo dyes: from medicinal chemistry to biomedical sciences. The latter benefits from azo dye application are related to imaging, drug delivery, photo-pharmacology and photo switching. Herein, we have compiled and discussed recent works on azo dye compounds obtained so far, focusing on their medicinal importance and future prospects.

Enhancing defect densities in SmErxFe1-xO3 nanostructures and tuning their electrical characteristics for photocatalytic and photoresponse functions

Owing to their distinct physicochemical traits nanostructured semiconductors continue to find immense potential in energy and environment friendly applications. From this point, SmErxFe1-xO3 systems were chemically synthesized and studied in detail for their photoresponse performance and photocatalytic behavior. The material characteristics were initially studied using several analytical tools that include X-ray diffraction (XRD), Raman and microscopic (SEM/TEM) instruments. Substitution of erbium (Er) ions at Fe sites was conceived using X-ray photoelectron spectroscopic (XPS) analysis. Optical band gap and their associated defect states in perovskites (upon Er replacement) was additionally evaluated using UV and PL data. Photocatalytic efficiency of SmErxFe1-xO3 was at first adjudged through comparative studies with SmFeO3 by involving effective treatment of organic dyes under visible light. Secondly, improved electrical conductivity in SmErxFe1-xO3 was capitalized on to fabricate p-n devices that demonstrated remarkable photoelectrical performance. Forward current and response ratio improved significantly in such devices. The bias conditions were also noted to proportionately improve the photo switching potential. Time-dependent photoresponse results affirmed the stability in processed devices. The improved application performance in SmErxFe1-xO3 nanostructures has been reasoned to effective substitution of Er ions, which tend to influence the O-Fe-O interactions and result with the observed electrical characteristics to facilitate the much needed improved charge transfer process.

Carrier conduction mechanisms of WSe2/p-type Ge epilayer heterojunction depending on the measurement temperature and applied bias

We have fabricated a WSe 2 /p-type Ge epilayer heterojunction and analyzed its electrical and carrier transport characteristics by temperature-dependent current–voltage ( I–V ) measurements in the range of 125–375 K. The WSe 2 /p-type Ge heterojunction showed rectifying I-V characteristics at room temperature. The ideality factor and barrier height of the heterojunction were strongly dependent on temperature, which could be attributed to the inhomogeneous barrier height at the interface. Different current transport mechanisms were observed with the changes in temperature and applied bias. The thermionic emission mechanism governed the carrier transport at temperatures higher than 250 K, while at temperatures below 250 K, the carrier conduction was dominated by tunneling. The I – V curves at low temperatures showed a shift of carrier transport mechanism from direct tunneling at lower voltages to Fowler–Nordheim tunneling at higher voltages. The WSe 2 /p-type Ge epilayer heterojunction exhibited a self-driven photo-switching property with a responsivity of 14.2 mAW −1 and photo-current/dark-current ratio of ∼9 at a wavelength of 900 nm. The results show the potential of the two-dimensional transition-metal dichalcogenide/bulk semiconductor heterojunction devices for opto-electronic applications. • Heterojunction by combining WSe 2 with p-type Ge epilayer grown on Si was fabricated. • Carrier conduction of WSe 2 /p-type Ge heterojunction was investigated. • Thermionic emission dominated the carrier transport in higher temperature region. • Direct and Fowler-Nordheim tunneling dominated carrier transport in lower temperature region. • Self-driven photo switching was observed with responsivity of 14.2 mAW −1 at 900 nm.

High performance trilayer MoS2 photodetector

The two-dimensional molybdenum disulfide (MoS2) material has attracted a lot of attention and research recently because of the outstanding properties including layer-strutured semiconductor material and a direct band gap. These properties make MoS2 to be great potential for application in electronics and optoelectronics. In this study, we fabricated and measured a photodetector made of trilayer MoS2 materials based on nanopore structure devices. The highly crystalline trilayer MoS2 films were synthesized and placed on top of the nanopore. The aluminum metal is then evaporated and contacted to both sides of this MoS2 film to form electrodes for conductivity measurement. The measured vertical trilayer MoS2 photodetector exhibited high photoresponsivity and photogain of about 105 A/W and 105, respectively. It is also found that the photo switching of photodetector is stable and reproducible with fast rise and decay times in milisecond scale. These characteristics make few-layer MoS2 device to work as optical switches for optoelectronic applications.

Modulation of the optoelectronic properties of a donor–acceptor conjugate between a cationic polythiophene and a peptide appended perylene bisimide ampiphile

The morphology of a cationic polythiophene changes from core–shell to a mixed fibrillar network with black spots, quenching of the PL-intensity and an enhanced photo switching property on addition of peptide appended perylene bisimide.

Novel Photoswitchable Dihetarylethenes Exhibiting Fluorescence.

Photochromic bridged dihetarylethenes exhibiting photochromism were synthesized. The synthesized coumarinyl(thienyl) thiazoles also display light regulated fluorescence in their open form. When the open form is irradiated with UV-light of wavelength less than 400nm, a significant decrease in fluorescence intensity is observed due to cyclisation. Again, when the cyclised isomeric form is irradiated with visible light of wavelength greater than 470nm the open form along with fluorescence is recovered. This reversible photo switching behaviour of dihetarylethenes may make them to be used as photo regulators. This phenomenon is also supported by DFT calculations.

Synthesis, liquid crystalline properties and photo switching properties of coumarin-azo bearing aliphatic chains: Application in optical storage devices

A series of novel azo-coumarin derivatives with different aliphatic chain length (3a-e) have been synthesized and characterized for liquid crystal properties and their photoswitching behavior. The incorporation of coumarin along with azobenzene was prepared via esterification reaction and differ in the length of alkyl group, CnH2n+1, where n = 6, 8, 10, 12 and 14. Azo-coumarin bearing C14 alkyl chain shows Smectic–A phase while azo-coumarin bearing rest of long alkyl chain exhibited Nematic phase. The incorporation of natural product moieties into azobenzene network has increased electron delocalisation and liquid crystal properties. The photoswitching properties of said molecules were tested and the coumarin-azo compounds 3a-e took ~46 s to reach photostationary state during UV illumination and exhibited long thermal back relaxation time (~16 h) in solutions. Device is also fabricated to see the performance of the device with respect to the alkyl chain length. Presented studies show the importance of azo-coumarin derivatives with different chain length for the application of optical storage devices.

Photoswitching and photocatalytic functions of SnxCu1−xS nanostructures

Ultra-thin semiconducting nanostructures are garnering strategic importance in energy and environment remediation applications. In this regard, SnxCu1−xS nanostructures were processed through an eco-friendly chemical route and investigated in detail for photoswitching and photocatalytic functions. X-ray diffraction, FT-IR, Raman, UV–vis absorbance and high-resolution microscopic tools were initially used to examine the physico-chemical traits of SnxCu1−xS nanostructures. Ambiguous evidence for the substitution of Sn ions in place of Cu ions was attained through X-ray photoelectron spectroscopy. The photocatalytic performance of SnxCu1−xS systems was investigated through effective remediation of organic dye molecules under visible light. Scavenger based photocatalytic experiments were additionally carried out to infer the degradation mechanism. Type II p-n SnxCu1−xS/In2S3 heterojunction diodes were also demonstrated for the first time with improved electrical conductivity and photoelectrical performances. The rectification ratio, forward current values and photo switching capabilities of these diodes were noted to improve in the Current vs. Voltage (I-V) and Current vs. Time (I-T) curves as a function of Sn composition and applied bias potential. The excellent photo switching stability augments the photo generated carriers to be effectively separated along the p-n junctions. The enhanced photoelectronic and photocatalytic functionalities in SnxCu1−xS has finally been reasoned to the improved charge transfer kinetics in the respective architectures, resulting from the effective Sn interaction in hexagonal host lattice.

Photosensing properties of ruthenium(II) complex-based photodiode

Ru(II) complex containing 2,6-di(1H-pyrazol-3-yl)pyridine ligand was synthesized to prepare organic-based photodiode. After forming the back contact with aluminum metal on p-Si by thermal evaporation, Al/Ru(II) complex/p-Si heterojunction was constructed by inserting Ru(II) complex organic layer into Si substrate. The fundamental electrical parameters and photosensing properties of fabricated heterojunction were investigated by current–voltage and capacitance–voltage measurements under the dark and different light intensities. The studied device exhibits a good rectifying property with rectification ratio of 2.4 × 104 at ± 7 V. It is observed that the photosensing properties such as light sensitivity and photoconductive responsivity of the photodiode based on Ru(II) complex are strongly dependent on the illumination power. The transient measurements show that the heterojunction device has a good photo switching property in the application of the photodiode, photoconductor and photocapacitor. The obtained results declare that the fabricated Ru(II)-based heterojunction device can be used in the organic-based optoelectronic device applications as a photodiode, photosensor, and optical sensor.

Surface induced charge transfer in CuxIn2-xS3 nanostructures and their enhanced photoelectronic and photocatalytic performance

Multi-functional semiconducting nanostructures are gaining popularity for application in photoelectronics, energy storage devices and also in industrial and environmental remediation functions. In this regard, CuxIn2-xS3 nanostructures were investigated in detail for their photoelectrical and photocatalytic performance. Their physico-chemical characteristics were at first studied using X-ray diffraction, Raman, UV–vis absorbance, X-ray photoelectron spectroscopy and high resolution electron microscopic tools. CuxIn2-xS3 based flip chip Schottky diodes were demonstrated to attest their improved conductivity and enhanced photoelectrical performance. The photo switching capabilities of a type II p-n CdTe/CuxIn2-xS3 heterojunction was also investigated. In both the device configurations, the current-voltage (I-V) characteristics revealed the forward current and rectification ratio to improve under lower threshold voltages. The time-dependent photoresponse characteristics affirmed the stability of diodes, augmenting the improved/effective separation of photo generated electron hole pairs under illumination. Additionally, the photocatalytic performances of CuxIn2-xS3 nanostructures were inferred under visible light conditions through effective remediation of methylene blue (MB) dye molecules. The obtained results infer the Cu interaction in tetragonal lattice of CuxIn2-xS3 to promote the surface induced charge transfer mechanism in respective nanostructures, thereby enhancing their photoelectronic and photocatalytic functionalities.

Excitation wavelength based reversible multicolour photoluminescence by a single chromophore upon aggregation: Detection of picric acid-application in bioimaging

In an attempt to achieve photo switching of multicolour photoluminescence on a unimolecular platform, herein we report a benzothiazole based probe as an excitation wavelength sensitive multicolour emitter in its aggregated state. Though in solution the blue emission overwhelms others, but in the dry state the emission in blue, green and red with intermediate yellow could be achieved. Further, the probe in its aggregated state detects picric acid in solution, solid and live cells, where blue emission is quenched in all the three working media while the red emission is activated in solid state and live cells. TD-DFT (time dependent density function theory) calculations were performed to understand the electronic properties and sensing behaviour of the probe. This probe constitutes a first example of detection of picric acid in human cancer cells to the best of our knowledge. The tuneable multicolour emission of the probe suggests its possible implementation in applications related to OLEDs.

Live Cell Palm Techniques for Super Resolution Imaging of Murine Cardiac Myocytes

Since their inception, super resolution methodologies have revolutionised the way in which biologists can visualise subcellular structures. Cardiac science has particularly benefited under these methodologies, as structures such as the dyads of cardiomyocytes have become resolvable, thus yielding new understanding of -their spatial organization. However, pairing of nanoscale dyadic structure and function has been hampered by the fact that techniques such as direct stochastic optical reconstruction microscopy (dSTORM) generally require fixed tissue. Furthermore, quantification of dSTORM images based on antibody labelling is complicated by variability in labelling efficacy, and displacement of the fluorophore from the protein of interest. We presently circumvented these limitations by creating a transgenic mouse expressing a photo activated red fluorescent protein tagged to ryanodine receptor 2 (PA-tag-RFP-RyR2). Imaging of live, isolated cardiomyocytes was attained with a commercial Zeiss Elyra dSTORM setup using the photo-activated light microscopy (PALM) technique. PA Tag RFP requires dual sample illumination with activation laser and imaging laser to produce constant photo switching. In our experiments we found that by adjusting the rate of activation and photobleaching from imaging we could optimize the blinking behaviour required for live cell PALM imaging. To reduce background, HILO and TIRF illumination were employed to reduce the thickness of the optical section. Our results show RyR localisation accuracy of 40nm in the X and Y plane for live cell images, in contrast to the higher resolution of 10-20nm in fixed samples with antibody labelling. RyR cluster arrangements in live cells were observed to be broadly in agreement with fixed samples. Ongoing work is aimed at linking RyR organization to local calcium release events (Ca2+ sparks), with focus on unravelling the functional consequences of the dynamic nature of RyR arrangement.

Super-resolution fluorescence blinking imaging using modified Fourier ptychography.

In this paper, we propose a new super-resolution imaging technique based on fluorescence blinking (SRFB). Contrary to structured illumination microscopy (SIM), SRFB considers the time-varying fluorescence distribution under a suitable density as the varying illuminated speckle pattern, and therefore, external speckle patterns or diffusers are not required. With several images recorded at different times, a super-resolution image can be obtained through an iterative algorithm modified from Fourier ptychography. Recorded image sequences in a microscopy imaging experiment based on photo switching or fluorescence blinking effects, such as STORM and SOFI, can be handled with SRFB and used to recover a super-resolution image. The simulation and experimental results confirm that the SRFB scheme can surpass the diffraction limit by a factor greater than two.

Molecular engineering of the photo switching in the ortho chromophores of the nanostructured green fluorescence protein

Green fluorescent protein (GFP) has attracted wide attention as an efficient fluorescent probe for photophysical properties studies in the biological and biochemical sciences. In this work, the effect of different substituents (OMe, OEt, NO2, Br, CN, and CF3) in the para position of the phenyl ring in 4-(2-hydroxybenzylidene)-1,2-dimethyl-1H-imidazol-5(4H)-one (o-HBDI), an analogue of the core chromophore of the GFP, on their photophysical properties were explored in both gas and solution phases by using TD-DFT method at PBE0/6-311++G(d,p) and M06-2X/6-311++G(d,p) levels of theory. The potential energy surfaces (PESs) were evaluated along the reaction coordinate (RC = dOH) at the ground S0 and excited S1 states of the three o-HBDI derivatives composed of electron donating and accepting substitutes in both gas and solution phases. The structural, electronic and photophysical properties, the atomic charges and electron density at critical points were examined. The results show the photophysical properties of o-HBDI are dependent on substitution patterns and solvents. In contrast to S0 state, the excited-state intramolecular proton transfer (ESIPT) process at S1 state in these compounds is expected to be approximately less barrier height. The ESIPT process in all three solvents is predicted to be an exergonic reaction. Depending on the strength of the electronic accepting or donating of the substituents, a wide tunable range of the fluorescence emissions from 460nm (visible blue light) to 642nm (visible red light) was predicted in the solvent media. By comparing wavelengths, the maximum value of the stoke shift is observed for CN-o-HBDI and TF-o-HBDI. Chromophores composed of the electron donating substituents (OMe and OEt) represent greatest red-shift in non-polar solvent cyclohexane. Our computed results are in good agreement with the experimental observations and have the potential applications in manipulating and tuning photo-physical properties of the technologically and biologically important fluorescent protein.

1D02 キラルアゾベンゼンの異性化によるネマチック-コレステリック相間の光スイッチング

1D02 キラルアゾベンゼンの異性化によるネマチック-コレステリック相間の光スイッチング

Preparation of azo-dye sensitized TiO2 photocatalyst for inhibition of E-Coli bacteria under visible light irradiation

The antibacterial activity of dye-sensitized semiconductor titanium dioxide films containing 4-{(E)-[4-(dimethylamino) phenyl] diazenyl} benzoic acid azo dye against E. coli was investigated as a model for Gram-negative bacteria. Several reports have been reported where metal complex have is used as dye, though sensitization of organic dye has not yet reported. These azo-dye sensitized TiO2 nanomaterials were characterized by XRD, SEM and UV-visible spectra. Spherical nature of TiO2 and sensitization can be seen from SEM images, XRD data suggest the particles in anatase form, photo switching of Azo-dye was studied using UV-Visible spectra. The bactericidal effects of films under UV-visible light irradiation were measured, experimental results indicate that these films inhibit the growth of Escherichia coli under UV light irradiation, the irradiation time could be considerably reduced and the bactericidal efficiency is related to the coverage of TiO2 films. With the increase in concentration of dye the activity was also increased.

Electrocatalytic Z → E Isomerization of Azobenzenes.

A variety of azobenzenes were synthesized to study the behavior of their E and Z isomers upon electrochemical reduction. Our results show that the radical anion of the Z isomer is able to rapidly isomerize to the corresponding E configured counterpart with a dramatically enhanced rate as compared to the neutral species. Due to a subsequent electron transfer from the formed E radical anion to the neutral Z starting material the overall transformation is catalytic in electrons; i.e., a substoichiometric amount of reduced species can isomerize the entire mixture. This pathway greatly increases the efficiency of (photo)switching while also allowing one to reach photostationary state compositions that are not restricted to the spectral separation of the individual azobenzene isomers and their quantum yields. In addition, activating this radical isomerization pathway with photoelectron transfer agents allows us to override the intrinsic properties of an azobenzene species by triggering the reverse isomerization direction (Z → E) by the same wavelength of light, which normally triggers E → Z isomerization. The behavior we report appears to be general, implying that the metastable isomer of a photoswitch can be isomerized to the more stable one catalytically upon reduction, permitting the optimization of azobenzene switching in new as well as indirect ways.

Synthesis and liquid crystalline behaviour of substituted (E)-phenyl-4-(phenyldiazenyl) benzoate derivatives and their photo switching ability

ABSTRACTAzobenzene derivatives containing phenyl/4-halogen-phenyl 4-{(E)-[4-(pent-4-en-1-yloxy)phenyl]diazenyl}benzoate group with different electronegative substituent (H, F, Cl, Br and I) at other end was synthesised. These azo-based benzoate derivatives have been characterised by FTIR, 1H-NMR, 13C-NMR, elemental analyser, POM and UV-Vis spectroscopy. Photosaturation at 358 nm obtained after 82 s of UV irradiation and the longest thermal back relaxation time of 45 h recorded by UV-Vis. The azo derivative could be possible photolock under UV light, as observed by the improved thermal back relaxation time. The resulting photolockable chain of azobenzene might prove valuable in the development of optical device application. These azobenzene moieties also exhibit liquid crystalline behaviour with respect to the halogen substitution as an electron withdrawing group shows that strong structure property relationship exists among them.

Effect of intrinsic polymer properties on the photo sensitive organic field-effect transistors (Photo-OFETs)

In this work, we have demonstrated how the intrinsic properties of a conjugated polymer can influence the electro-optical characteristics of photo sensitive organic field - effect transistors (Photo-OFETs). Photo-OFETs fabricated with three batches of poly[2-methoxy,5-(3′,7′-dimethyl-octyloxy)]-p-phenylene vinylene (MDMO-PPV) were investigated in the scope of our work. Photo-OFETs were fabricated with the polymers, than electrically and electro-optically characterized. It was observed that the channel current and the field-effect mobility increase with increasing polymer molecular weight. Interestingly, the electro-optical characteristics and photo switching properties of the transistors were found to depend on the polydispersity (PDI) of the polymer as well. These results are explained in terms of influences of chain packing, ordering and trap density on the FET switching properties and transistor parameters.

Light-enhanced liquid-phase exfoliation and current photoswitching in graphene-azobenzene composites.

Multifunctional materials can be engineered by combining multiple chemical components, each conferring a well-defined function to the ensemble. Graphene is at the centre of an ever-growing research effort due to its combination of unique properties. Here we show that the large conformational change associated with the trans–cis photochemical isomerization of alkyl-substituted azobenzenes can be used to improve the efficiency of liquid-phase exfoliation of graphite, with the photochromic molecules acting as dispersion-stabilizing agents. We also demonstrate reversible photo-modulated current in two-terminal devices based on graphene–azobenzene composites. We assign this tuneable electrical characteristics to the intercalation of the azobenzene between adjacent graphene layers and the resulting increase in the interlayer distance on (photo)switching from the linear trans-form to the bulky cis-form of the photochromes. These findings pave the way to the development of new optically controlled memories for light-assisted programming and high-sensitive photosensors.