Spiropyran and spironaphthoxazine based opto-chemical probes for instant ion detection with high selectivity and sensitivity to trace amounts of cyanide

Photoswitchable Photochromic Chelating Spironaphthoxazines: Synthesis, Photophysical Properties, Quantum-Chemical Calculations, and Complexation Ability

The stable and efficient photochromic and photoswitchable molecular systems designed from spirooxazines are of increasing scientific and practical interest because of their present and future applications in advanced technologies. Among these compounds, chelating spironaphthoxazines have received widespread attention due to their efficient optical response after complexation with some metal ions being of biomedical interest and environmental importance, as well as their good cycle performance and high reliability, especially by metal ion sensing. In this mini-review, we summarize our results in the design of novel photoswitchable chelating spironaphthoxazines with specific substituents in their naphthoxazine or indoline ring systems in view of recent progress in the development of such molecular systems and their applications as metal ion sensors. The design, synthesis methods, and photoresponse of such spirooxazine derivatives relevant to their applications, as well as quantum-chemical calculations for these compounds, are presented. Examples of various design concepts are discussed, such as sulfobutyl, hydroxyl, benzothiazolyl, or ester and carboxylic acid as substituents in the chelating spironaphthoxazine molecules. Further developments and improvements of this interesting and promising kind of molecular photoswitches are outlined.

Photoresponsive reversible self-assembly of rod-coil amphiphiles containing spiropyran groups

Stimuli-responsive assembly deformation is a key feature in constructing smart soft materials, which makes them versatile and autonomous. In this study, rod-coil amphiphilic compounds containing spiropyran (SP) groups were developed and synthesized to investigate their stimuli-responsive assembly in a solution system with 99% water content. In addition to photochromic phenomena, reversible light-mediated morphological alterations occurred in these molecular aggregates. Based on the different flexible chain segments of rod-coil amphiphiles, the initial assemblies underwent a dissociation-reassembly process under ultraviolet (UV) irradiation, whereupon they deformed or disassembled to assemblies. Furthermore, as the UV source was removed, the original nanostructures were gradually recovered again via the ring-closing reaction process. These compounds, interestingly, can selectively combine with copper ions to produce cross-linked co-assembled nanostructures. The copper ion complex solution of rod-coil amphiphilic compounds emitted unique bright blue fluorescence, which allowed for the specific visual identification of copper ions in aqueous solutions.

A Modern Look at Spiropyrans: From Single Molecules to Smart Materials

Photochromic compounds of the spiropyran family have two main isomers capable of inter-switching with UV or visible light. In the current review, we discuss recent advances in the synthesis, investigation of properties, and applications of spiropyran derivatives. Spiropyrans of the indoline series are in focus as the most promising representatives of multi-sensitive spirocyclic compounds, which can be switched by a number of external stimuli, including light, temperature, pH, presence of metal ions, and mechanical stress. Particular attention is paid to the structural features of molecules, their influence on photochromic properties, and the reactions taking place during isomerization, as the understanding of the structure-property relationships will rationalize the synthesis of compounds with predetermined characteristics. The main prospects for applications of spiropyrans in such fields as smart material production, molecular electronics and nanomachinery, sensing of environmental and biological molecules, and photopharmacology are also discussed.

Fabrication of graphene-based sensor for exposure to different chemicals

Opto-chemical sensors are the most significant type of sensors that are widely used to detect a variety of volatile organic compounds and chemicals. This research work demonstrates the fabrication and characterization of an opto-chemical sensor based on a graphene thin film. A 300 nm graphene thin film was deposited on clean glass with the help of RF magnetron sputtering. The structure, surface and quality of the graphene thin film were characterized using XRD, SEM and Raman spectroscopy. For optical characterization, the thin film was exposed to IPA, acetone and toluene (separately) for five, ten and fifteen minutes. The optical transmission was then observed via UV-NIR spectroscopy in the near-infrared range (900 to 1450 nm). The thin film of graphene has expressed a sharp response time and recovery time with high sensitivity for each chemical. However, by comparing the output of the graphene thin film in response to each chemical, it was observed that graphene thin film has a better transmission and sensing rate for exposure to toluene.

Spiropyran-Merocyanine Based Photochromic Fluorescent Probes: Design, Synthesis, and Applications

Due to ever-increasing insights into their fundamental properties and photochromic behaviors, spiropyran derivatives are still a target of interest for researchers. The interswitching ability of this photochrome between the spiropyran (SP) and merocyanine (MC) isoforms under external stimuli (light, cations, anions, pH etc.) with different spectral properties as well as the protonation-deprotonation of its MC form allows researchers to use it suitably in sensing purposes by developing different colorimetric and fluorometric probes. Selective and sensitive recognition can be achieved by little modification of its SP moiety and functional groups. In this review, we emphasize the recent advancements (from 2019 to 2022) of spiropyran-merocyanine based fluorogenic and chromogenic probes for selective detection of various metal ions, anions, neutral analytes, and pH. We precisely explain their design strategies, sensing mechanisms, and biological and environmental applications. This review may accelerate the improvements in designing more advanced probes with innovative applications in the near future.

Preparation of Photoswitchable Polyacrylic Nanocomposite Fibers Containing Au Nanorods and Spiropyran: Optical and Plasmonic Properties

Photoswitchable nanofibers and nanocomposite fibers containing plasmonic nanoparticles have attracted a great deal of interest in optical and plasmonic devices. Herein, photoswitchable poly(methyl methacrylate-co-vinylimidazole-co-spiropyran ethyl acrylate) (MVSP) and its copolymer with butyl acrylate (MBVSP) were prepared via emulsion polymerization, and the corresponding nanofibers (MVSP@NF and MBVSP@NF) and nanocomposite fibers (MVSP/Au@NF and MBVSP/Au@NF) containing AuNRs were fabricated through electrospinning. FTIR and ¹H NMR analyses confirmed the progress of the copolymerization reaction. The morphology of the prepared nanofibers containing AuNRs with an aspect ratio of 2.5 was identified by SEM and TEM techniques. The inclusion of vinylimidazole into the copolymer chains resulted in well-dispersed AuNRs. Photoisomerization studies revealed a higher photochromic efficiency for MBVSP@F (reflective intensity of 37.4%) with respect to MVSP@NF (reflective intensity of 62.5%) because of the greater flexibility of the chains. In addition, the presence of AuNRs in the nanocomposite fibers with high absorptivity intensified the photochromic properties for both samples. The polarization-dependent plasmonic band of AuNRs was switched between 650 and 634 nm through the photoisomerization of nonpolar SP to polar MC reversibly for MVSP/Au@NF. This displacement was just 4 nm for MBVSP/Au@NF, owing to the limited coupling between AuNRs and MC isomers. Besides, the capability of both nanocomposite fibers for reversible optical patterning was investigated by fast write-erase cycles. Enhanced photofatigue resistance in those fibers and the photomodulation of the plasmonic band of AuNRs using SP to MC isomerization revealed their promising potential for optical patterning and on-demand real-time plasmonic devices.

A benzothiazole-based new fluorogenic chemosensor for the detection of CN- and its real-time application in environmental water samples and living cells

Since the cyanide ion is used in a wide range of industries and is harmful to both human health and the environment, a number of research efforts are dedicated to creating fluorescence sensors for the detection of cyanide (CN-). Herein, for the fluorescence detection of CN-, a new highly selective and sensitive sensor 2-(3-(benzo[d]thiazol-2-yl)-4-hydroxybenzylidene)-1H-indene-1,3(2H)-dione (BID) was created by conjugating a benzothiazole moiety with 1H-indene-1,3(2H)-dione. The donor and acceptor components of this hybrid receptor were covalently connected through a double bond. The nucleophilic addition of a cyanide anion to the BID inhibits the intramolecular charge transfer (ICT) transition, resulting in spectral and colour alterations in the receptor. When the solvent polarity was increased from n-hexane to methanol, this molecule exhibited a bathochromic shift in the emission wavelength (610 to 632 nm), suggesting the presence of a solvatochromic action. The sensor BID has shown strong specificity towards CN- by interrupting its internal charge transfer (ICT), resulting in a significant change in the UV-vis spectrum and a notable blue shift in the fluorescence emission spectrum. The cyanide anion (CN-) is responsible for the optical alterations observed by BID, as opposed to the other anions examined. The detection limit was 5.97 nM, significantly less than the WHO's permitted amount of CN- in drinking water. The experimental findings indicate that BID's fluorescence response to CN- is pH insensitive throughout a wide pH range of 6.0 to 12.0. The interaction mechanism between the BID and CN- ions has been studied by HRMS, 1H-NMR titration experiments, FT-IR, and DFT, which confirmed the nucleophilic addition of CN- on vinylidene and subsequent disturbance of ICT. Additionally, we demonstrated the real-time detection application of CN- in environmental water samples and live-cell imaging.