Experimental and theoretical investigations of cyanide detection using a photochromic naphthopyran

Photochromic naphthopyran derivatives were synthesised for anion recognition applications. The crystal structure, experimental and theoretical investigation of photochromic and anion sensing properties of a simple naphthopyran derivative were investigated. The naphthopyran derivative displayed good fatigue resistance and selective sensing response towards cyanide ions. The mechanism of complex formation was suggested based on NMR studies. Theoretical calculations were performed to understand the experimental results. An excellent correlation between the theoretical and experimental data was observed.     

Controlled conversion of isomers in a hybrid biphotochromic system

[reaction: see text] The photochromic performance of a hybrid system connecting naphthopyran and dithienylethene was investigated, and the photochemistry of eight different isomers was explored by choosing an appropriate wavelength of light.     

Thin film photochromic materials: Effect of the sol-gel ormosil matrix on the photochromic properties of naphthopyrans

Photochromic naphthopyran derivatives have been embedded in sol-gel prepared organically modified thin films. The introduction of organic functional groups into a silica matrix allows tailoring the surface of its pores and the polarity of the environment of the embedded host molecules. The photochromic properties of the naphthopyran molecules, such as the spectral properties of the coloured forms and the kinetics of the thermal bleaching, depend strongly on the polarity of the pores where the molecules are located and, hence, on the nature and loading of organic functional groups in the composition of the ormosil matrix. Important changes in the photochromic properties of the films have also been induced by modifications in the sol-gel preparation and processing parameters. The photostability of the photochromic molecules upon prolonged exposition to UV light is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix, where the dye molecules will be located, affects the stability of the molecules, in terms of the effectiveness of the interaction between the photochromic molecules and the pore surface.     

Photochromism and Metal Complexation of a Macrocyclic Styryl Naphthopyran

A macrocyclic benzo‐15‐crown‐5 ether unit tethered to a photochromic naphthopyran by a styryl spacer ( MEN ) is shown to form a 1:1 complex with magnesium(II). The structure and dynamics of the specific host–metal interactions were investigated by PFG‐NMR analysis. A combination of UV/Vis and variable temperature multi‐dimensional ¹H NMR photokinetic analysis of the crown‐containing styryl naphthopyran and its metal complex was used to probe the effect of metal complexation on the photochromism.     

Thermally reversible photochromic behaviour of new naphthopyrans involving an intramolecular [2+2] cyclization reaction

New 4-(2,2-diphenylethenyl)naphthopyrans were synthesized and their photochromic behaviour in solution were studied under continuous UV light irradiation conditions. Although only one coloured photoproduct was expected to be formed, due to the naphthopyran substitution pattern, NMR analysis on degassed UV irradiated solutions, performed at low temperature, showed the formation of different compounds. Among them, the main product is formed through an intramolecular [2+2] cyclization reaction and show thermally reversible photochromic properties.     

萘并吡喃光致变色荧光开关研究进展

萘并吡喃及其衍生物是经典的光致变色材料,具有很低的背景颜色、优良的光致变色抗疲劳性、易于调控的变色动力学、开环体具有宽的吸收等优点,受到了研究者的重视。本文综述了近几年来作者课题组利用萘并吡喃构建光致变色荧光开关的研究进展,通过将荧光基团和萘并吡喃以掺杂模式、共聚物和有机小分子等形式构建光致变色荧光开关,研究了它们在溶液和薄膜中的荧光开关性能,初步探讨了萘并吡喃荧光开关在非破坏性读出和荧光成像等方面的应用潜能。     

Photostability of a photochromic naphthopyran dye in different sol-gel prepared ormosil coatings

A photochromic naphthopyran derivative was embedded in sol-gel prepared thin ormosil films. The resulting samples show high transparency and exhibit a strong red colouration upon irradiation with UV light. The photostability of the photochromic molecules is strongly related to the nature of the embedding ormosil matrix. The introduction of organic functional groups into the inner pore surface of the matrix allows tailoring the chemical environment where the dye molecules will be allocated, in terms of the effectiveness of the interaction between the photochromic molecules and the Si-OH groups on the surface of the pores, affecting the stability of the molecules upon prolonged exposition to UV light. The photostability of the molecules was increased in matrices functionalized with larger organic groups, or with larger amount of modifying groups. In this way the photodegradation of the photochromic molecules could be reduced by a factor of 5, as compared with the photodegradation of the molecules in unfunctionalized silica matrix.     

Spectrokinetic studies on new bi-photochromic molecules containing two naphthopyran entities

A range of new bi-photochromic molecules containing two identical (3a-d) or two distinct naphthopyran units (6a-d), linked through the phenyl substituents located on the sp³ hybridised pyran ring carbon atom, using conjugated and non-conjugated spacers, have been synthesised from bis-propynols and (substituted)naphthols. Study of the spectrokinetic properties of these compounds under near UV-vis continuous irradiation conditions revealed that the two naphthopyran units are stimulated independently leading to open forms with higher colourabilities but without affecting the individual bleaching kinetics. Compared to the individual photochromic components and to model mono-photochromes it was observed that the nature of the bridge has a small effect on the photochromic properties of each system.     

2,2-二芳基取代萘并吡喃类光致变色化合物的合成与性能研究

从光消色速度和最大吸收强度两个角度出发, 用Grignard试剂和萘并吡喃-2|酮合成了一系列2,2-二芳基取代萘并吡喃类光致变色化合物, 并用 1H NMR, IR, MS和元素分析确定其结构. 研究了其紫外-可见光谱, 并探讨了紫外-可见光谱和光致变色性能之间的关系, 分析了其结构和光消色速度之间的关系, 初步探索到光消色速度快慢和取代基位置之间的规律, 为实用化的有机光致变色化合物的合成提供了有价值的参考依据.     

Synthesis, photochromic properties, and light-controlled metal complexation of a naphthopyran derivative

A light-controlled reversible binding switch based on photochromic 3H-naphtho[2,1-b]pyran is under development for studying cellular oscillatory calcium signals. The binding affinities of the closed and open forms of substituted naphthopyran 1 for Ca(2+), Mg(2+), and Sr(2+) in buffer were determined. The photochemically ring-opened form of the receptor exhibited increased affinity compared to the thermally stable closed form of the receptor. The binding affinity difference for Ca(2+) was approximately 77-fold at pH 7.6.     

Comprehensive photokinetic and NMR study of a biphotochromic supermolecule involving two naphthopyrans linked to a central thiophene unit through acetylenic bonds

A photophysical and photochemical study of a biphotochromic compound where two naphthopyran units are linked by an acetylene-thiophene-acetylene bridge has been carried out in toluene. Both fluorescence and intersystem crossing to the triplet manifold were found to compete with the photocoloration process. Two photoproducts (transoid-trans and transoid-cis stereoisomers), absorbing at approximately 480 nm and corresponding to the opening of a single photochromic unit, were detected by spectrophotometric analysis after short irradiation time in diluted solution and identified by 1H-nuclear magnetic resonance (NMR) spectroscopy. After prolonged irradiation at 228 K of highly concentrated solutions (up to 3 x 10(-3) mol dm(-3)), two additional isomers, absorbing at approximately 550 nm, were formed. Their NMR spectra indicate the opening of both photochromic units. An interesting effect of selective vibronic excitation was found, showing that the photoreaction is favored at excited vibronic levels to the detriment of the radiative relaxation.     

Synthesis and photochromic properties of substituted naphthopyran compounds

A group of 3,3-diaryl-3H-naphtho[2,1-b]pyran compounds with functional substituents at the 5- and 6-positions of the naphthopyran skeleton and the para positions at the 3-aryl moieties were prepared through condensation reactions between 2-naphthol derivatives and 1,1-diarylprop-2-yn-1-ol derivatives. The chemical structures of the compounds were confirmed by NMR and MS. The crystal structure of 3,3-diphenyl-6-morpholino-3H-naphtho[2,1-b]pyran (4b) was determined and the relationship between the pyran substructure and photochromism was discussed. The photochromic properties were studied as well, and decoloration kinetics of colored forms was fitted to the biexponential model. Among these compounds, 4b was considered to be the best one due to the large ΔOD of colored form, which is one of the most important properties used in the photochromic material.     

Photochromic hybrid sol–gel films containing naphthopyrans

Abstract  

Several photochromic benzo- and naphthopyrans were embedded in hybrid organic–inorganic ureasilicate based films obtained by a sol–gel process. The resulting films, containing 0.1% (w/w) of the photochromic compound, were transparent and flexible and for naphthopyrans they were colourless or presented just a slight colouration. Under UV continuous irradiation the films developed a significant absorption in the visible region that fades in the dark with variable kinetics depending on the naphthopyran structure. 2,2-Diphenyl-3H-naphtho[2,1-b]pyran films showed a very fast colouration under UV light giving rise to coloured open forms, containing mainly the TC isomer (98%) along with a very small amount of the more stable TT isomer (2%), that practically returned to the initial absorbance in 1 min.     

Rapid decoloration and acidichromism of photochromic 3,3-diaryl-3H-pyrano[3,2-f]quinolines

Pyranoquinoline, with its light-sensitive fragment and coordination node, provides an ideal matrix for the development of multi-functional photochromic compounds. This paper presents the synthesis and photochromic properties of 3,3-diaryl-3H-pyrano[3,2-f]quinoline derivatives QP1-QP8. All exhibited good photochromism under UV light irradiation followed by biexponential kinetic decay in the dark at ambient temperature. Their photochromic processes were reversible, and acidichromism was observed to occur in solution. The fading speeds of QP2 and QP6 were higher than those of their known naphthopyran counterparts, whereas the decoloring speeds of the six other compounds were all over an order of magnitude higher than those of QP2 and QP6. The synthesized pyranoquinolines exhibited very good fatigue resistance both in solution and the solid state. Compared to other pyranoquinolines, the optical densities of QP2 and QP6, i.e., the compounds with 2,4-dimethoxylphenyl and 1-naphthyl, were enhanced dramatically. For all the synthesized pyranoquinolines, a distinct bathochromic shift was observed with increasing solvent polarity. The structure-property relationship of the pyranoquinolines was revealed through the single-crystal X-ray analysis of QP1 and QP7.     

Spiropyrans and spirooxazines. 3. Synthesis of photochromic 5′-(4,5-diphenyl-1,3-oxazol-2-yl)-spiro[indoline-2,3′-naphtho[2,3-<Emphasis Type="Italic">b</Emphasis>]pyran]

The reaction of 2-hydroxy-3-(4,5-diphenyl-1,3-oxazol-2-yl)-1-naphthaldehyde with 1,2,3,3-tetramethyl-3H-indolium perchlorate afforded photochromic spiro[indoline-2,3′-naphthopyran] containing a 4,5-diphenyloxazole group in position 5′ of the naphthopyran fragment. The merocyanine form of the spiropyran gave complexes with bivalent heavy cations.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 693–697, March, 2005.     

Synthesis and photochromic properties of tricarbonylchromium complexes of 2H‐η6‐benzochromenes

Although in the 2H‐chromene (benzopyran) series complexation with tricarbonylchromium, under thermal conditions, is totally regioselective, in the naphthopyran series the same reaction cannot be observed. We show here that with tricarbonyl(trispyridine)chromium as complexing agent, in the presence of Lewis acid, complexation of naphthopyrans can be achieved and is totally regioselective. The complexes formed are photochromic compounds, and their thermal bleaching kinetic constants are reduced as compared with the non‐complexed homologous compound. Copyright © 2000 John Wiley & Sons, Ltd.     

Designing naphthopyran mechanophores with tunable mechanochromic behavior

Mechanochromic molecular force probes conveniently report on stress and strain in polymeric materials through straightforward visual cues. We capitalize on the versatility of the naphthopyran framework to design a series of mechanochromic mechanophores that exhibit highly tunable color and fading kinetics after mechanochemical activation. Structurally diverse naphthopyran crosslinkers are synthesized and covalently incorporated into silicone elastomers, where the mechanochemical ring–opening reactions are achieved under tension to generate the merocyanine dyes. Strategic structural modifications to the naphthopyran mechanophore scaffold produce dramatic differences in the color and thermal electrocyclization behavior of the corresponding merocyanine dyes. The color of the merocyanines varies from orange-yellow to purple upon the introduction of an electron donating pyrrolidine substituent, while the rate of thermal electrocyclization is controlled through electronic and steric factors, enabling access to derivatives that display both fast-fading and persistent coloration after mechanical activation and subsequent stress relaxation. In addition to identifying key structure–property relationships for tuning the behavior of the naphthopyran mechanophore, the modularity of the naphthopyran platform is demonstrated by leveraging blends of structurally distinct mechanophores to create materials with desirable multicolor mechanochromic and complex stimuli-responsive behavior, expanding the scope and accessibility of force-responsive materials for applications such as multimodal sensing.

Structure–activity relationships for strategic substitution of the naphthopyran mechanophore scaffold enable polymeric materials with tunable mechanochromic behavior.     

Study on fluorescent switching of naphthopyran with carbazole and pyrene dyad immobilized on SBA-15

A naphthopyran-bridge-carbazole dyad (CzNP), which exhibits both fluorescence and photochromism was synthesized. Then the CzNP was grafted into SBA-15-NH₂, with particular focus on how the SBA-15-NH₂ affects the photoswitching fluorescence change properties. A double fluorescence photochromic material, which was prepared by reacting 1-Pyrenecardboxaldehyde(PY-CHO):naphthopyran-carbazole(CzNP)=1:1 (molar ratio) with SBA-15-NH₂ was also synthesized. Naphthopyran in this two systems displayed excellent photochromic performance. The fluorescent emission was modulated between ‘on’ and ‘off’ via the photoisomerization of naphthopyran in high-degree, especially in PY-CzNP-SBA-15-NH₂ (>90%) due to the photoinduced energy transfer from pyrene excimers to the opened-form naphthopyran and the photoinduced electron transfer between carbazoles and the opened-form naphthopyran moiety. Both the fluorescence photoswitching CzNP-SBA-15-NH₂ and PY-CzNP-SBA-15-NH₂ in CH₃CN/H₂O (v/v, 1:1) solution displayed excellent fatigue resistance. The structural characteristics of CzNP-SBA-15-NH₂ and PY-CzNP-SBA-15-NH₂ were measured by FTIR spectra, X-ray diffraction (XRD), and Elemental analysis.     

The use of poly(alkylene oxide)s to achieve fast and controlled photochromic switching in rigid matrices

We report a conjugation system for the enhancement of photochromic dye performance in rigid matrices using widely available, cheap, chemically robust and compatible polymeric starting materials, namely poly(propylene oxide) (PPO) and poly(1,2‐butylene oxide). Conjugation of these soft (low T_g) polymers to an indeno‐fused naphthopyran photochromic dye, in a telechelic geometry, gives access to a wide range of accelerated and tuned fade speeds (decoloration) via variation in molecular weight. The t_1/2 and t_3/4 fade speeds for PPO conjugates (polymer molecular weights ranging between ca. 425 and 2000) are accelerated by 35–58 and 51–76%, respectively, compared with the nonconjugated control dye. Longer oligomers provide faster decoloration approaching that obtained in solution. The stability of the polyethers allows functionalization using a wide variety of chemistries, including harsh acid catalyzed transformations, providing an overall facile synthesis of photochromic dye‐polymer conjugates in high yield and purity. In addition, these polymers give easy access to conjugates with star‐type architectures, which provide an even further improvement in performance compared with their linear counterparts with less conjugated polymer needed per dye to achieve a given fade speed. © 2012 Commonwealth of Australia. J Polym Sci Part A: Polym Chem, 2012     

Regulation of Charge Delocalization in a Heteronuclear Fe2Ru System by a Stepwise Photochromic Process

Heteronuclear complexes FeCp₂?DTE?C?C?Ru(dppe)₂Cl ( 1 o ; dppe=1,2‐bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp₂?DTE?C?C?Ru(dppe)₂?C?C?DTE?FeCp₂ ( 2 oo ), with redox‐active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe???Ru electronic communication. Upon UV‐light irradiation of 2 oo , the Fe???Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo → 2 co → 2 cc ; this is ascribed to the gradual increase in π‐conjugated systems. The near‐infrared absorptions in mixed‐valence species [ 2 oo ]⁺/[ 2 co ]⁺/[ 2 cc ]⁺ are gradually intensified following the conversion of [ 2 oo ]⁺→[ 2 co ]⁺→[ 2 cc ]⁺, which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes.