[Show abstract][Hide abstract] ABSTRACT: We investigate the physicochemical properties of a novel imidazolium benzospiropyran derivative, SP(Im), in imidazolium based ionic liquids (ILs). SP(Im) was prepared through alkylation of an imidazole to the photoswitchable compound and this derivative was characterised in imidazolium based ILs with increasing chain length to examine the stability of its merocyanine (MC) and spiropyran (SP) forms and compared to standard spiropyran, BSP. The rate of thermal relaxation of the new derivative is found to be about ten times faster than that of BSP as reflected in rates of 13.9 x 10(-3) s(-1) and 1.0 x 10(-3) s(-1) for SP(Im) and BSP, respectively, in [C(6)mIm][NTf(2)]. Since ILs are believed to form nano-structured domains it is proposed that the covalent attachment of the imidazolium side group of SP(Im) fully integrates the photoswitchable moiety into the non-polar region through side-chain association. In contrast, unbound BSP is relatively free to migrate between both polar and non-polar regions and the MC form is more readily stabilised by the IL charge via through space interactions and spontaneous movement to charged nano-domains leading to enhancement of the MC lifetime. At higher concentrations, rheological and transport properties were investigated to determine the impact of covalent attachment of the BSP fragment to an imidazolium cation on the ionic liquid structure. Ionic conductivity was found to decrease by up to 23% for SP(Im) with effects increasing with cation side-chain length. Unlike BSP, the photoswitching of the SP(Im) did not affect conductivity or viscosity values. This may indicate that the mobility of the photoswitchable compound and the resulting disruption of such movement may be critical to the control of this physical property.
[Show abstract][Hide abstract] ABSTRACT: Switchable materials have tremendous potential for application in sensor development that could be applied to many fields. We are focusing on emerging area of wireless sensor networks due to the potential impact of this concept in society. Spiropyran-based sensors are probably the most studied type of photoswitchable sensing devices. They suffer from many issues but photofatigue, insufficient selectivity and lack of sensitivity are probably the most important characteristics that hinder their wider application. Here, we are address these issues and demonstrate that covalent attachment of modified spiropyran into a polymeric film significantly reduces photodegradation. The observed signal loss after 12th cycle of switching between the spiropyran and merocyanine forms is only about 27% compared to the loss of 57% of the initial signal in an equivalent experiment based on non-immobilized spiropyran. This has enabled us to demonstrate at least five reversible cycles of detection of an ion of interest (in our case H+) with minimal signal loss. Furthermore, we demonstrate that the sensitivity can be increased by incorporation of additional binding groups in the parent spiropyran molecule. Using molecular modelling to calculate the relevant bond lengths as a measure of interaction between MC and H+, the calculated increase of H-bond strength is approximately an order of magnitude for a derivative containing a methoxy group incorporated in the o-position of the parent spiropyran in comparison to the equivalent unsubstituted phenol. This theoretical result was found to correspond very well with experimental observation. As a result, we have increased the sensitivity to H+ by approximately one order of magnitude.
Full-text · Article · Aug 2009 · Journal of Photochemistry and Photobiology A Chemistry
[Show abstract][Hide abstract] ABSTRACT: Novel modified spirooxazines (SOs) with additional chelating groups were synthesised and the crystal structure of one of these was determined. UV-vis spectroscopic characterization of the photoisomerization of the SO derivatives shows that the photochromic behaviour is altered with Zn(2+) coordination. In particular, addition of a group as in carboxylic acid 5 to the indole section of the SO increases the lifetime of the merocyanine Zn(2+) complex by 20-fold compared to the methylated indole 6. (C) 2009 Published by Elsevier Ltd.
No preview · Article · May 2009 · Tetrahedron Letters
[Show abstract][Hide abstract] ABSTRACT: Spiropyran derivatives have been immobilised on the surface of polystyrene microbeads using different
immobilisation strategies. These functionalised polymeric beads can be reversibly switched between the
colourless inactive spiropyran (SP) and highly coloured (purple) active merocyanine (MC) forms using
low power light sources, such as light-emitting diodes (LEDs). A UV LED (375 nm) is used for the SP
/MC conversion, and a white LED (430–760 nm) for the reverse MC/ SP conversion. The
photochromic behaviour of the coated beads has been characterised using different LEDs and
reflection spectroscopy, employing optic fibres and an in-house-designed holder. Investigations into the
metal-ion binding behaviour of the spiropyran-modified microbeads have shown that Cu2+ ions cause
an appreciable colour and spectral change when brought into contact with the beads in the MC form,
suggesting that a significant interaction is occurring. However, the Cu2+ ions can be completely expelled
by photonic-conversion of the beads into the inactive SP form using a white LED. This sequence has
been successfully repeated six times, suggesting that it is possible to cycle through activation of the
functionalised beads from a non-binding to a binding form (SP / MC) using a UV LED, allow
binding with Cu2+ ions to occur, and subsequently, expel the bound ions and regenerate the passive SP
surface using a white LED. Other metals, such as calcium, do not cause any appreciable colour or
spectral change over the same concentration range and in the presence of the same anion (final
concentration 7.1 104 M nitrate salt in ethanol). The system is therefore self-indicating in terms of
whether the active MC or inactive SP forms are present, and whether Cu2+ ions are bound to the MC
form. In principle, therefore, these functionalised beads could form the basis of a photoswitchable
stationary phase for metal ion binding and detection: irradiation of the stationary phase with UV LEDs
causes retention of guest species due to the presence of the MC form, while subsequent exposure to
white LEDs causes release of guest species into the mobile phase
Full-text · Article · Oct 2008 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: In the crystal structure of the title compound, C(19)H(17)Cl(2)NO, the indoline and benzopyran ring systems are approximately perpendicular to each other. The indoline ring is in an envelope conformation with the spiro C atom as the flap. The N atom of the indoline ring forms a pyramidal environment, the sum of the angles at this atom being 352.46°.
[Show abstract][Hide abstract] ABSTRACT: In the crystal structure of the title compound, C19H17Cl2NO, the indoline and benzopyran ring systems are approximately perpendicular to each other. The indoline ring is in an envelope conformation with the spiro C atom as the flap. The N atom of the indoline ring forms a pyramidal environment, the sum of the angles at this atom being 352.46°.
Full-text · Article · Jan 2008 · Acta Crystallographica Section E Structure Reports Online
[Show abstract][Hide abstract] ABSTRACT: Here, we discuss an interesting concept that brings an added flexibility in chemo/bio sensing. We present system that can be switched photonically between two states, only one of which exhibits ion-binding behaviour. The system is based on molecular photoswitch spiropyran, which is probably the most studied compound exhibiting above characteristics. Upon irradiation with UV light the passive spiropyran (SP) molecule undergoes a heterocyclic ring cleavage that results with the formation of the merocyanine (MC) which is zwitterionic form capable of ion binding. In contrast to the uncharged and colourless spiropyran form, the merocyanine form is highly charged and can be utilized as ligand for other charged species. Moreover, it is strongly coloured, and the colour tells us which form is present. In addition it provides interesting information about the immediate environment of the merocyanine binding site (e.g. polarity, presence of certain ions etc.). In this work, we present a SP-based system in which SP is immobilized and protected within a polymeric matrix. Such system may be used for detection of metal ions in highly polar solvents, e.g. water. The response characteristics and kinetics of MC-Cr3+ complex formation and SP-MC switching within the polymer matrix have been determined. Simple light emitting diodes (LEDs) have been employed for photoswitching and colorimetric measurement of SP-MC switching and MC-Cr3+ complex formation as light sources and detectors.
[Show abstract][Hide abstract] ABSTRACT: In science, control of interactions at the molecular scale is the ultimate goal, as this in turn determines all macroscale behaviour. Using molecular-switches based on spiropyran-like molecules, it is possible to produce surfaces whose physico- chemical properties can be controlled under external photonic stimulation . It has been demonstrated that low-power light sources such as UV and green LEDs can switch spiropyran-modified surfaces between an inactive spiro (SP) form and an active merocyanine (MC) form which is highly coloured, and possesses a phenolate binding site for metal guest species such as Cu2+ , Co2+ . Similarly, aminoacids interact with the MC form through complementary zwitterionic charges . The amino acid and metal ion 'guests' can be subsequently expelled using a green LED to reform the original inactive SP . These processes have been observed in liquid phase experiments, but recently, in order to generate smart adaptive surfaces based on spiropyran photochromic moieties, we have covalently bound spiropyran derivatives to the surface of polystirene microspheres.
Full-text · Article · Feb 2007 · Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference
[Show abstract][Hide abstract] ABSTRACT: We report a new direct route for the selective preparation of novel partial cone O-aryl ether calixarenes to be used as new platforms for the preparation of non-aggregated dyes. These partial cone conformers have the aromatic substituents lying within the calixarene annulus via the upper rim.
No preview · Article · Jan 2007 · Tetrahedron Letters
[Show abstract][Hide abstract] ABSTRACT: Two homochiral tripodal receptors were characterised by X-ray crystallography, the first examples for this class of imidazolium receptor. These receptors were also screened for anion recognition. Both receptors demonstrated selectivity towards chloride and bromide with binding constants as high as 16,000.
No preview · Article · Jan 2007 · Tetrahedron Letters
[Show abstract][Hide abstract] ABSTRACT: A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calixarene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.
No preview · Article · Aug 2006 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: Emerging technologies create new application fields but few of them require that we completely rethink our approach in preparation and characterization of sensors. The vision of internet scale wireless sensor networks (WSNs) requires the deployment of enormous numbers of sensors. This necessarily means that the cost of each sensor must be brought down significantly if this vision is to be realized.
An ideal solution for this problem would be a sensor that does not interact with its environment in any way until there is a need for measurement. Upon the measurement, the sensor’s surface is completely regenerated and returned into the state as before the measurement. This step is critical as it ensures that the measurement did not any effect on the sensor hence no calibration is necessary.
In our work, we use compounds that indeed can be switched between the active and passive state using light. Most commonly used compounds are so called spiropyrans (SP) and spirooxazines (SO). Here we show the recent advance in preparation of reversible, light-modulated sensors using surface immobilised SP/SO derivatives. A further attractive property of these materials is that they are inherently self-indicating through striking colour changes that enable the state to be easily determined (active vs. passive), and the presence of a bound guest to be detected. These spectral changes enable a range of self-diagnostic tests to be incorporated that enable binding events to be controlled at the surface interface, and for real binding events to be distinguished from artefacts arsing from changes in light intensity, or photobleaching of the active component. We have identified most notable problems for utilization of these compounds in “calibrationless” sensors such as relatively weak binding constants, photodegradation, and unfavourable kinetics of switching between the active and passive state and we demonstrate our approach in solving these problems.