Photochromic Dithienylethene Units Research Articles

Photoswitchable electron-rich phosphines: using light to modulate the electron-donating ability of phosphines.

The synthesis and properties of photoswitchable electron-rich phosphines containing N-heterocyclic imines equipped with a photochromic dithienylethene unit are reported. Heteronuclear NMR spectroscopy and UV/vis studies reveal that the imine substituents undergo reversible electrocyclic ring-closing and ring-opening reactions upon exposure to UV and visible light, respectively. The photoisomerization alters the electron-donating ability of the phosphines by up to ΔTEP = 8 cm-1.

Photoswitchable Nitrogen Superbases: Using Light for Reversible Carbon Dioxide Capture.

Using light as an external stimulus to alter the reactivity of Lewis bases is an intriguing tool for controlling chemical reactions. Reversible photoreactions associated with pronounced reactivity changes are particularly valuable in this regard. We herein report the first photoswitchable nitrogen superbases based on guanidines equipped with a photochromic dithienylethene unit. The resulting N‐heterocyclic imines (NHIs) undergo reversible, near quantitative electrocyclic isomerization upon successive exposure to UV and visible irradiation, as demonstrated over multiple cycles. Switching between the ring‐opened and ring‐closed states is accompanied by substantial pK a shifts of the NHIs by up to 8.7 units. Since only the ring‐closed isomers are sufficiently basic to activate CO2 via the formation of zwitterionic Lewis base adducts, cycling between the two isomeric states enables the light‐controlled capture and release of CO2.

Photoresponsive Dithienylethene-Containing Tris(8-hydroxyquinolinato)aluminum(III) Complexes with Photocontrollable Electron-Transporting Properties for Solution-Processable Optical and Organic Resistive Memory Devices.

The rational design of a new class of photoresponsive tris(8-hydroxyquinolinato)aluminum(III) (Alq3) complexes has been developed. By incorporating the photochromic dithienylethene units with different peripheral heterocycles into the Alq3 framework, the photochromic properties as well as photoswitching efficiency can be readily modulated, through effective photocyclization of the Al(III) complex. Such intrinsic photochromic behavior leads to the unprecedented enhancement in the electron-transporting properties as demonstrated by the as-fabricated electron-only device, rendering the realization of photoswitchable electron mobility. In addition, one of these complexes is capable of serving as an active layer for solution-processable resistive memory devices. Photocontrollable memory performance has been achieved with a binary memory behavior, with high ON/OFF ratio and long retention time. This work represents not only the first example of photoresponsive Alq3-based electron-transporting materials but also the solution-processable Alq3-based optical and resistive memory devices with photocontrollable performance.

Synthesis, characterization, and properties of some bisacetylide and binuclear acetylide gold(I) compounds based on the photochromic dithienylethene unit

We report the synthesis and characterization of two new bisacetylide compounds, 1,2-bis(2-ethynyl-5-methyl-3-thienyl)perfluorocyclopentene and 1-[2-methyl-5-phenyl-3-thienyl]-2-[4-methyl-2,5-bis(ethynyl)-3-thienyl]hexafluorocyclopentene together with three dinuclear acetylide gold(I) complexes LAu-CC-dithienylethene-CC-AuL in which L = PPh3 or PCy3, containing the photochromic dithienylethene unit. The photophysical properties of these new complexes are compared and contrasted with those of some previously reported dithienylethene complexes. It has been revealed that these compounds with dithienyletehene units show photochromic behavior, but their absorption spectra, cyclization/cycloreversion quantum yields, and efficiencies of the photochromic process and conversions from the open- to the closed-ring isomers in the photostationary state, are all highly dependent on the substitution sites of the bisalkynyl moiety and whether or not there is bisalkyne metalation. The photochromic process was also found to show complete reversibility by alternating irradiation with UV and visible light.

Controlling the Stepwise Closing of Identical DTE Photochromic Units with Electrochemical and Optical Stimuli

The full or stepwise controlled closing of identical photochromic dithienylethene units in the same molecule was addressed with a combination of electrochemical and optical stimuli in a trimetallic carbon-rich ruthenium complex.

Photoswitching of the second-order nonlinearity of a tetrahedral octupolar multi DTE-based copper(i) complex

The modulation of the quadratic NLO response of an octupolar metal-based chromophore featuring four photochromic dithienylethene units is reported. Quantum mechanical simulations are consistent with a full switching of the DTE units and reproduce the strong enhancement of the NLO response.

New Light on the Ring–Chain Equilibrium of a Hydrogen‐Bonded Supramolecular Polymer Based on a Photochromic Dithienylethene Unit and its Energy‐Transfer Properties as a Storage Material

A novel, bifunctional, quadruple hydrogen-bonding ureido-pyrimidinone (UPy) unit bridged by photochromic dithienylethene (1) has been synthesized, which affords linear assemblies in solution and undergoes concentration-dependent ring-opening polymerization. The two UPy functional groups of 1 can dimerize intramolecularly to form a cyclic monomer with the two thienyl rings fixed in a parallel conformation, which prohibits its photocyclization. We exploited the photochemical reactivity and resonance difference of the linker of the bis-UPy derivative as well as using the more typical (1)H NMR, DOSY, and Ubbelohde viscometry methods to investigate for the first time the ring-chain polymerization mechanism. Moreover, we fabricated a mixed polymer film with a fluorescent dye noncovalently endcapping the linear photochromic assemblies through quadruple hydrogen bonds, which showed nondestructive fluorescent read-out ability for data storage by fluorescence resonance energy transfer (FRET) from the fluorescent dye to the closed form of the diarylethene.

Photochromic Organometallics with a Dithienylethene (DTE) Bridge, [YCCDTECCY] (Y={MCp*(dppe)}): Photoswitchable Molecular Wire (M=Fe) versus Dual Photo‐ and Electrochromism (M=Ru)

Dinuclear acetylide-type complexes bridged by a photochromic dithienylethene unit (DTE), [Y-C[triple bond]C-DTE-C[triple bond]C-Y] 1 (Y={MCp*(dppe)}; Cp*=pentamethylcyclopentadienyl, M=Fe (1(Fe)), Ru (1(Ru))), have been prepared, and their wirelike and switching behavior, as well as their oxidation chemistry has been investigated. The DTE complexes 1 exhibit photochromic behavior in a manner similar to organic DTE derivatives; UV irradiation causes ring closure of the open isomer 1O to form the closed isomer 1C and visible-light irradiation of the resultant 1C causes reverse ring opening to regenerate 1O. But the performance is dependent on the metals. With respect to the interconversion rates and the 1C content at the photostationary state under UV irradiation, the ruthenium complex 1(Ru) is superior to the iron analogue 1(Fe). The wirelike performance is associated with the photochromic processes, and the efficient switching performance has been verified for 1(Fe) as characterized by the V(ab) values [V(ab) is the electronic coupling derived from intervalence charge-transfer (IVCT) bands: V(ab)(1(Fe)C; ON)=0.047 eV versus V(ab)(1(Fe)O; OFF)=0 eV], and are also supported by the large switching factor (SF=K(C)(C; ON)/K(C)(O; OFF)=39; K(C)=comproportionation constant). SF for 1(Ru) is determined to be 4.2. The remarkable switching behavior arises from the different pi-conjugated systems in the two isomeric forms, that is, cross-conjugated (1O) and fully conjugated pi-systems (1C). It was also found that, in contrast to the reversible redox behavior of the iron complex 1(Fe), the ruthenium complex 1(Ru)O undergoes oxidative ring closure to form the dicationic species of the closed isomer 1(Ru)C(2+) and, thus, the ruthenium system 1(Ru) shows dual photo- and electrochromism. The distinct oxidation behavior of 1(Fe) and 1(Ru) can be ascribed to the spin distribution on the diradical intermediates 1(Fe)O(2+) and 1(Ru)O(2+), as supported by DFT calculations.

Symmetric Six-Fold Arrays of Photo- and Electrochromic Dithienylethene Switches

The direct synthesis of six-fold symmetric hexaphenylbenzenes with multiple photochromic dithienylethene units via a cobalt-catalyzed cyclotrimerization is reported. This approach allows for six photochromic units to be held in proximity with a well-defined spatial separation without affecting the photochromic properties of each unit.

Dithienylcyclopentenes-Containing Transition Metal Bisterpyridine Complexes Directed toward Molecular Electronic Applications

There is continuing interest in the design and synthesis of functional materials for applications in molecular electronics and information storage. Of particular interest are systems that can provide multiple means for controlling transport through well-defined and stable electronic and/or redox states. We report herein the synthesis and characterization of a system containing transition-metal complexes along with dithienylethene (DTE) units so as to achieve photo and redox control of transport. A facile synthetic methodology was developed to assemble and couple metal terpyridine (M-tpy) complexes with the photochromic DTE unit in a linear structure with M-DTE-M or DTE-M-DTE arrangements, with emphasis on the latter series. The photochromic properties of these assemblies were examined by monitoring the changes in their UV/vis spectra upon irradiation at specific wavelengths capable of triggering the open/closed isomerization in the DTE units. Their electrochromic properties were studied via cyclic voltammetry and controlled potential electrolysis experiments. Complexes 10 (PhDTE-Fe-DTEPh) and 11 (PhDTE-Co-DTEPh) with phenyl-ending groups were found to be both photochromic and electrochromic, so they represent excellent candidates for further elaborations. The Fe(II)-containing complex 8 (ClDTE-Fe-DTECl) with chloride-ending groups was photochromically inactive but could undergo the electrochemically induced open-to-closed isomerization. On the contrary, the electrochromically inactive complex 9 (ClDTE-Co-DTECl) underwent cyclization under ultraviolet irradiation.

On/Off Photoswitching of the Electropolymerizability of Terthiophenes

In this contribution the polymerization of terthiophene, to form an alkene bridged alpha,alpha-coupled sexithiophene polymer, is controlled by light; i.e. the electropolymerizability of the monomer 1F is switched off and on with UV and visible light, respectively. The system comprises of both bis-terthiophene and photochromic dithienylethene units. The presence of a light-switchable unit allows on-off switching of the electropolymerization of the monomer with light. Furthermore the incorporation of the dithienylethene in the polymer backbone increases dramatically the homogenity of the polymer formed (i.e., only sexithiophene units are formed). The derived films are robust and fully retain electrochromic behavior as has been demonstrated through cyclic voltammetry while spatial control (patterning) is readily achieved by applying simple optical masking techniques.

High‐Content Pendant Photochromic Copolymer with Dithienylethene/Fluorene 2:1 Mole Ratio

AbstractSummary: Two photochromic dithienylethene units were incorporated into one fluorene unit as a monomer and the mole ratio of photochromic unit/repeat unit reached to 2:1 using this monomer. The content of dithienylethene component in the polymer could be improved effectively by polymerization of this monomer, which contains more than one dithienylethene units. All the starting materials concerned in the synthesis are commercially available and so the synthesis could be performed on a large scale. The polymer obtained by typical palladium‐catalyzed Suzuki coupling reaction is photochromic both in solution and in solid state and possesses good solubility. The photochromic and photomodulation luminescence properties of the polymer are also presented.Structure of the photochromic polymer based on dithienylethene.magnified imageStructure of the photochromic polymer based on dithienylethene.

Photocontrolled release and uptake of a porphyrin guest by dithienylethene-tethered beta-cyclodextrin host dimers.

Two photoswitchable dithienylethene-tethered beta-cyclodextrin dimers were synthesized to function as host molecules with an externally controllable binding affinity. The cyclodextrin cavities of these dimers are linked through their secondary sides by a photochromic dithienylethene unit that is connected to the secondary rim either directly (4) or through propyl spacers (9). Irradiation with light switches these dimers between a relatively flexible (open) and a rigid (closed) form. The binding properties of the dimers depend on the configuration of the dithienylethene spacer, as is shown by microcalorimetry performed with tetrakis-sulfonatophenyl porphyrin (TSPP) as a guest molecule. The differences in binding properties are most pronounced for the more rigid dimer 4, which binds TSPP 35 times more strongly in the open form (4 a) than in the closed form (4 b). The values found for the enthalpy of binding (deltaH degrees ) indicate that this difference in binding is due to the loss of cooperativity between the two beta-cyclodextrin cavities in the closed form. Molecular modeling shows that 4 b is not able to bind TSPP effectively in both cyclodextrin cavities. The open and closed forms of the more flexible dimer 9 show no substantial difference in their binding of TSPP. Thermodynamic values indicative of strong binding of TSPP by two beta-cyclodextrin cavities were measured for both forms of the dimer, and molecular modeling confirms that both are flexible enough to tightly bind TSPP. The binding differences between the forms of dimer 4 allow the photocontrolled release and uptake of TSPP, which renders control of the ratio of complexed to free TSPP in solution possible.

A photoresponsive laser dye containing photochromic dithienylethene units

A novel molecule, containing two photochromic dithienylethene moieties linked to a fluorescent bis(phenylethynyl)- anthracene residue has been prepared, and shows a reversible change in its fluorescence quantum yield from 0.001 to 0.83, and a corresponding increase in laser emission intensity, on exposure to UV light.