A comparative study of the photochromic compounds incorporated on the surface of nanoparticles

Electric Properties of Photochromic Molecules Physisorbed on Silver and Copper Nanoparticles

This paper investigates the electric properties of the photochromic dihydroazulene/vinylheptafulvene system as it is physisorbed onto silver and copper nanoparticles. Our focus is on how the polarizability and hyperpolarizability of the dihydroazulene, s-cis-vinylheptafulvene, and s-trans-vinylheptafulvene molecules depend on molecular orientation with respect to the nanoparticles, the molecule-cluster separation, and the type of nanoparticle. The computational approach utilizes a combined quantum mechanical/molecular mechanical method in which the molecules are treated quantum mechanically while the nanoparticles are treated with a simpler classical method. The molecules are described with density functional theory. The electric properties are calculated using response theory utilizing the long-range-corrected functional CAM-B3LYP and the correlation consistent basis set aug-cc-pVDZ. The atoms of the nanoparticles are represented using atomic polarizabilities. The interactions between the nanoparticles and the molecular systems are calculated using a polarizable embedding scheme after which the molecular properties are calculated with time-dependent density functional theory. The results show that the electric properties are indeed affected by the presence of the nanoparticles. It is also clear that it is the hyperpolarizabilities that change the most while the polarizabilities are less affected. Furthermore, the influence of the nanoparticles on the molecules depends heavily on the relative molecular orientation with respect to the nanoparticles and molecular conformation. Finally, it is observed that a copper nanoparticle has a larger influence on the molecular systems than a silver nanoparticle.

Spectroscopic and Physicochemical Studies on 1,2,4-Triazine Derivative

A novel 5-(5-Bromo-2-hydroxybenzylidene)-6-oxo-3-phenyl-5,6-dihydro-1,2,4-triazine-2(1H)-carbothioamide (4) “compound 4” was synthesized. The chemical structure of compound 4 was confirmed with spectroscopic techniques. Thermal analysis (TGA/dTGA) studies were conducted for identifying the kinetic thermodynamic parameters and the thermal stability of the synthesized compound 4. Cyclic voltammetric studies were performed for recognizing electrochemical characteristics of the synthesized compound 4. The calculated highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and the band gap were found to be −3.61, −5.32, and 1.97 eV, respectively. Using a diffused reflectance spectroscopy (DRS) technique, the estimated values of the optical band transitions of compound 4 in powder form were found to be 2.07 and 2.67 eV. The structural properties of thermally evaporated compound 4 thin films were analyzed using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. It was found that compound 4 has a triclinic crystal structure. The optical transitions and the optical dispersion factors of compound 4 thin films were investigated using a UV-Vis spectroscopy technique. From the UV-Vis spectroscopy technique, Egind=3.6 V was estimated for both the as-deposited and annealed thin films. For the as-deposited film, there were two photoluminescence (PL) emission peaks centered at 473 and 490 nm with a shoulder at 422 nm. For the annealed film at 423 K, there were five PL emission peaks centered at 274, 416, 439, 464, and 707 nm with a shoulder at 548 nm. The dark electrical conduction of compound 4 thin film was through a thermally activated process with activation energy equaling 0.88 eV.

Photoswitchable Binary Nanopore Conductance and Selective Electronic Detection of Single Biomolecules under Wavelength and Voltage Polarity Control

We fabricated photoregulated thin-film nanopores by covalently linking azobenzene photoswitches to silicon nitride pores with ∼10 nm diameters. The photoresponsive coatings could be repeatedly optically switched with deterministic ∼6 nm changes to the effective nanopore diameter and of ∼3× to the nanopore ionic conductance. The sensitivity to anionic DNA and a neutral complex carbohydrate biopolymer (maltodextrin) could be photoswitched "on" and "off" with an analyte selectivity set by applied voltage polarity. Photocontrol of nanopore state and mass transport characteristics is important for their use as ionic circuit elements (e.g., resistors and binary bits) and as chemically tuned filters. It expands single-molecule sensing capabilities in personalized medicine, genomics, glycomics, and, augmented by voltage polarity selectivity, especially in multiplexed biopolymer information storage schemes. We demonstrate repeatedly photocontrolled stable nanopore size, polarity, conductance, and sensing selectivity, by illumination wavelength and voltage polarity, with broad utility including single-molecule sensing of biologically and technologically important polymers.

Design and Study of a Photo-Switchable Polymeric System in the Presence of ZnS Nanoparticles under the Influence of UV Light Irradiation

Recent progress in the field of photosensitive materials has prompted a need to develop efficient methods to synthesize materials with basic intermolecular architectural designs and novel properties. Accordingly, in this work we design and study a photoactive polymer as a photo-switchable polymeric system in the presence and absence of ZnS nanoparticles (average size < 10 nm) at 5 wt.%. The influence of UV light irradiation on its properties were also studied. The photoactive block copolymer was obtained from styrene (S) and methyl methacrylate (MMA) as monomers and 1-(2-hydroxyethyl)-3,3-dimethylindoline-6-nitrobenzopyran (SP) was grafted to the block copolymer backbone as a photochromic agent. Furthermore, the incorporation of ZnS (NPs) as photo-optical switch component into the system enhances the purple colored photo-emission, with the open form of the spiropyran derivative (merocyanine, MC). The ZnS stabilize the isomeric equilibrium in the MC interconversion of the photochromic agent. The photo-switchable properties of the PS-b-PMMA-SP in the presence of ZnS (NPs) were examined using UV-VIS spectroscopy, Photoluminescence (PL) spectroscopy, optical fluorescence and scanning electronic microscopy (SEM-EDX.). The observed changes in the absorbance, fluorescence and morphology of the system were associated to the reversible interconversion of the two states of the photochromic agent which regulates the radiative deactivation of the luminescent ZnS NPs component. After UV irradiation the photoactive polymer becomes purple in color. Therefore, these basic studies can lead to the development of innovative functional and nanostructured materials with photosensitive character as photosensitive molecular switches.

"Click-switch" - one-step conversion of organic azides into photochromic diarylethenes for the generation of light-controlled systems

Diarylethenes (DAEs) are an established class of photochromic molecules, but their effective incorporation into pre-existing targets is synthetically difficult. Here we describe a new class of DAEs in which one of the aryl rings is a 1,2,3-triazole that is formed by “click” chemistry between an azide on the target and a matching alkyne–cyclopentene–thiophene component. This late-stage zero-length linking allows for tight integration of the DAE with the target, thereby increasing the chances for photomodulation of target functions. Nineteen different DAEs were synthesized and their properties investigated. All showed photochromism. Electron-withdrawing groups, and in particular −M-substituents at the triazole and/or thiophene moiety resulted in DAEs with high photo- and thermostability. Further, the chemical nature of the cyclopentene bridge had a strong influence on the behaviour upon UV light irradiation. Incorporation of perfluorinated cyclopentene led to compounds with high photo- and thermostability, but the reversible photochromic reaction was restricted to halogenated solvents. Compounds containing the perhydrogenated cyclopentene bridge, on the other hand, allowed the reversible photochromic reaction in a wide range of solvents, but had on average lower photo- and thermostabilities. The combination of the perhydrocyclopentene bridge and electron-withdrawing groups resulted in a DAE with improved photostability and no solvent restriction. Quantum chemical calculations helped to identify the photoproducts formed in halogenated as well as non-halogenated solvents. For two optimized DAE photoswitches, photostationary state composition and reaction quantum yields were determined. These data revealed efficient photochemical ring closure and opening. We envision applications of these new photochromic diarylethenes in photonics, nanotechnology, photobiology, photopharmacology and materials science.

New photochromic diarylethenes are reported in which one aryl ring is a 1,2,3-triazole that is formed by “click” chemistry between an azide on the target and a matching alkyne–cyclopentene–thiophene component.

Visible to near-IR molecular switches based on photochromic indoline spiropyrans with a conjugated cationic fragment

Photochromic molecules which can absorb and emit light within the "biological window" (650-1450 nm) are of great interest for using in various important biomedical applications such as bio-imaging, photopharmacology, targeted drug delivery, etc. Here we present three new indoline spiropyrans containing conjugated cationic fragments and halogen substituents in the 2H-chromene moiety which were synthesized by a simple one-pot method. The molecular structure of the obtained compounds was confirmed by FT-IR, ¹H and ¹³C NMR spectroscopy (including 2D methods), HRMS, elemental and single crystal X-ray analysis. Photochemical studies revealed the photochromic activity of spiropyrans at room temperature which caused photoswitchable fluorescence in the near-IR region after UV-irradiation. While the spirocyclic forms of compounds demonstrated absorption bands in the UV-Vis spectra with maxima in the visible region at about 445 nm and were not fluorescent, the photogenerated merocyanine isomers absorbed in the near-IR range at 708-738 nm and emitted at 768-791 nm. It was found that compound 1a with fluorine substituent possesses the most red-shifted absorption and emission bands of merocyanine form among all the known photochromic spiropyrans with maxima at 738 and 791 nm correspondingly. TD DFT calculations have shown that the longest wavelength absorption maxima of the merocyanine forms correspond to S₀-S₁ transitions of the isomers with at least one trans-trans-trans-configured vinylindolium fragment which brings them closer to cyanine-like structure and causes an appearance of the absorption and emission bands in the near-IR region.

The influence of nanoparticles on the excitation energies of the photochromic dihydroazulene/vinylheptafulvene system

This paper studies how nanoparticles affect photochromic systems, focusing on the influence of gold nanoparticles on the optical properties of the dihydroazulene/vinylheptafulvene (DHA/VHF) system.

Green and efficient synthesis of pyranopyrazoles using [bmim][OH−] as an ionic liquid catalyst in water under microwave irradiation and investigation of their antioxidant activity

Green and speedy synthesis of bispyranopyrazoles. [bmim][OH⁻] ionic liquid. Microwave irradiation. Antioxidant activity compared to vitamin E and C.