Photochromic Dithienylethene Research Articles

Study on NIR Optical Rewritable Film Based on Dithienylethene and Upconversion Nanocrystals

Tm3+ and Yb3+ codoped NaYF4 upconversion (UC) nanoparticles (NPs) with intense ultraviolet (UV) fluorescence were synthesized using a solvothermal approach. NIR optical rewritable film incorporated with the UCNPs and dithienylethene (DTE) were performed for optical storage based on the photochromic reaction of DTE induced by the intense UV from themultiphoton UC fluorescence of NaYF4NPs. The photochromic DTE did not exhibit obvious fatigue after repetitious write/erase cycles using NIR/green irradiation.

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.

Diarylethene-Containing Cyclometalated Platinum(II) Complexes: Tunable Photochromism via Metal Coordination and Rational Ligand Design

The synthesis, characterization, electrochemistry, photophysics and photochromic behavior of a new class of cyclometalated platinum(II) complexes [Pt(C(∧)N)(O(∧)O)] (1a-5a and 1b-5b), where C(∧)N is a cyclometalating 2-(2'-thienyl)pyridyl (thpy) or 2-(2'-thienothienyl)pyridyl (tthpy) ligand containing the photochromic dithienylethene (DTE) unit and O(∧)O is a β-diketonato ligand of acetylacetonato (acac) or hexafluoroacetylacetonato (hfac), have been reported. The X-ray crystal structures of five of the complexes have also been determined. The electrochemical studies reveal that the first quasi-reversible reduction couple, and hence the nature of lowest unoccupied molecular orbital (LUMO) of the complexes, is sensitive to the nature of the ancillary O(∧)O ligands. Upon photoexcitation, complexes 1a-3a and 1b-3b exhibit drastic color changes, ascribed to the reversible photochromic behavior, which is found to be sensitive to the substituents on the pyridyl ring and the extent of π-conjugation of the C(∧)N ligand as well as the nature of the ancillary ligand. The thermal bleaching kinetics of complex 1a has been studied in toluene at various temperatures, and the activation barrier for the thermal cycloreversion of the complex has been determined. Density functional theory (DFT) calculations have been performed to provide an insight into the electrochemical, photophysical and photochromic properties.

Amphiphilic Diblock Copolymer with Dithienylethene Pendants: Synthesis and Photo‐Modulated Self‐Assembly

In this work, an amphiphilic diblock copolymer (PEG(43)-b-PSDTE(29)) bearing photochromic dithienylethene (DTE) pendants is synthesized by reversible addition fragmentation chain transfer radical polymerization. The diblock copolymer was characterized by spectroscopic methods and gel permeation chromatography. The analyses proved the well-defined structure and narrow molecular weight distribution of the diblock copolymer. The DTE pendants could undergo reversible photoisomerization between their open and closed forms in solution when irradiated with UV and visible light as indicated by (1)H NMR and UV-vis spectroscopy. Hollow vesicle-like structures were formed by gradually adding deionized water to the colorless PEG(43)-b-PSDTE(29open) (DTE in open form) tetrahydrofuran solution. Under the same conditions, the aggregates formed in the blue PEG(43)-b-PSDTE(29close) (DTE in closed form) solution were colloidal spheres with solid interiors. The isomerization of DTE pendants could cause the deformation of the vesicle-like structures. The above results demonstrate a kind of novel photo-modulated self-assembly behavior of the amphiphilic diblock copolymer, which could be used for drug-delivery and other applications.

Linear and Nonlinear Optical Properties of Cationic Bipyridyl Iridium(III) Complexes: Tunable and Photoswitchable?

A series of cationic Ir(III) substituted bipyridyl ()(N(∧)N (N(∧)N-bpy) complexes incorporating electron-donor and -acceptor substituents, [Ir(C(∧)N-ppy-R')(2)(N(∧)N-bpy-CH═CH-C(6)H(4)-R)][X] (X(-) = PF(6)(-) or C(12)H(25)SO(3)(-)), 2 (a, R = NEt(2) and R' = Me; b, R = O-Oct and R' = Me; c, R = NO(2) and R' = C(6)H(13); C(∧)N-ppy = cyclometalated 2-phenylpyridine, [Ir(C(∧)N-ppy-Me)(2)(N(∧)N-bpy-CH═CH-thienyl-Me)][PF(6)], 2d, and the dithienylethene (DTE)-containing complex 2e have been synthesized and characterized, and their absorption, luminescence, and quadratic nonlinear optical (NLO) properties are reported. Density functional theory (DFT) and time-dependent-DFT (TD-DFT) calculations on the complexes facilitate a detailed assignment of the excited states involved in the absorption and emission processes. All five complexes are luminescent in a rigid glass at 77 K, displaying vibronically structured spectra with long lifetimes (14-90 μs), attributed to triplet states localized on the styryl-appended bipyridines. The second-order NLO properties of 2a-d and related complexes 1a-d with 1,10-phenanthrolines have been investigated by both electric field induced second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques. They are characterized by high negative EFISH μβ values which decrease when the ion pair strength between the cation and the counterion (PF(6)(-), C(12)H(25)SO(3)(-)) increases. The EFISH response is mainly controlled by metal-to-ligand charge-transfer/ligand-to-ligand charge-transfer (MLCT/L'LCT) processes. A combination of HLS and EFISH techniques is used to evaluate both the dipolar and octupolar contributions to the total quadratic hyperpolarizability, demonstrating that the major contribution is controlled by the octupolar part. The incorporation of a photochromic DTE unit into the N(∧)N-bpy ligand (complex 2e) allows the luminescence to be switched ON or OFF. The photocyclisation of the DTE unit can be triggered by using either UV (365 nm) or visible light (430 nm), leading to an efficient quenching of the ligand-based 77 K luminescence, which can be restored upon irradiation of the closed form at 715 nm. In contrast, no significant modification of the EFISH μβ value is observed upon photocyclization, suggesting that the quadratic NLO response is dominated by the MLCT/L'LCT processes, rather than by the intraligand excited states localized on the substituted bipyridine ligand.

Color change of redox-active organometallic dithienylethene complexes by photochemical and redox processes

Photochromic dithienylethene (DTE) derivatives, DTE–MCpL 2 {M = Fe, Ru; Cp = η 5-cyclopentadienyl; L 2 = (CO) 2, (CO)PPh 3, dppe (dppe = Ph 2PCH 2CH 2PPh 2)}, with a directly σ-bonded, redox-active organometallic attachment have been prepared and their response to photo- and electrochemical stimuli has been investigated. It turns out that the color of the organometallic derivatives can be controlled not only by photochromic processes but also by one-electron redox processes. The Ru complexes 1 Ru and 2 Ru exhibit reversible photochromism in a manner similar to organic DTE derivatives, with ring closing and ring opening triggered by UV and visible-light irradiation, respectively. Their photochromic behavior is critically dependent on both of the central metal and ligands. One-electron oxidation of the Fe complex 3 Fe gives the corresponding radical cationic species with a visible absorption.

Reversible photoswitching of dye-doped core–shell nanoparticles

We present a simple and versatile mechanism for the reversible photoswitching of dye-doped core-shell nanoparticles. Photochromic dithienylethenes are incorporated into the outer shell, close enough to the dyes entrapped in the core to efficiently quench them by energy transfer when photoconverted with UV light. The emission can be switched back on by irradiation with λ > 450 nm.

Photo- and electro-chromic organometallics with dithienylethene (DTE) linker, L2CpM-DTE-MCpL2: Dually stimuli-responsive molecular switch

Photochromic dithienylethene (DTE) derivatives, M-DTE-M (M: M(η(5)-C(5)R(5))L(2); M = Fe, Ru; R = H, Me; L = CO, phosphine), with direct σ-bonded, redox-active organometallic attachments are prepared and their response to photo- and electro-chemical stimuli as well as wire-like and switching performance has been investigated. These properties turn out to be dependent on the metal and the auxiliary ligands. The DTE complexes with the MCp(CO)(2) and RuCp(CO)(PPh(3)) fragments undergo reversible photochemical ring-closing and -opening of the DTE moiety upon UV and visible-light irradiation, respectively, whereas the other FeCp(CO)(PPh(3)) and Fe(η(5)-C(5)R(5))(dppe) derivatives are virtually inert with respect to the photochemical ring closing process. Electrochemical analysis of the DTE complexes reveals that 2e-oxidation of the open isomer O also brings about the ring closure of the DTE moiety to afford the Fischer-carbene-type, dicationic closed derivatives C(2+) with the π-conjugated system different from that in the neutral ones C obtained photochemically. Subsequent reduction of C(2+) furnishes the neutral closed species C. Thus the ring closure is mediated not only by the conventional photochemical process but also by the sequential oxidation-reduction process, i.e. the organometallic DTE complexes are found to be dually photo- and electro-chromic. It is notable that the oxidative procedures are viable for the photochemically inert derivatives. Wire-like and switching performance has been evaluated on the basis of the comproportionation constant K(C) for the 1e-oxidized mixed valence monocationic species obtained by the electrochemical analysis and the switching factor SF (K(C)(C)/K(C)(O)), respectively. The K(C)(C) (7.5 × 10(4)) and SF values (5.4 × 10(3)) for phosphine-substituted derivatives are significantly large, as a result of the distinct π-conjugated systems of the DTE moieties involved in the O- (with cross-conjugation) and C-forms (fully conjugated). Compared to the previously reported acetylide-type complexes bridged by a DTE linker, (dppe)Cp*M-C≡C-DTE-C≡C-MCp*(dppe), both parameters have been significantly improved by factors of ~150. Time-dependent DFT analysis for the photochemical processes has revealed that the ring-closing process occurs not only via the ligand centered singlet excited state but also via the ligand centered triplet state resulting from energy transfer processes between the ligand- and metal-centered excited states and that this proposed mechanism can account for the photochemical reactivity of ruthenium complexes superior to that of the corresponding iron derivatives.

Adsorption of a single molecule of a diarylethene photochromic dye on Cu(111)

On the route to single (large) molecule unimolecular chemistry, the adsorption of a photochromic dithienylethene dye on Cu(111) at a submonolayer level has been studied by Ultra High Vacuum-Scanning Tunneling Microscopy at Low Temperature. This technique has shown that the observed adsorbed molecule's shape is compatible with an helical conformation but has also revealed a surrounding electronic corrugation due to the perturbed surface states. Careful examination of the standing wave pattern indicated that only a part of the molecule is indeed interacting with the metallic substrate. Geometric considerations were used to infer that the bridging ethene moiety could be responsible for the electronic scattering. Scanning Tunneling Spectroscopy has shown a substantial amount of charge transfer from the surface to the adsorbate. The hypothesis that this precise double bond is a reactive locus toward charge transfer processes is confirmed by the electrochemical results: this double bond is indeed reduced upon coulometric reduction on glassy carbon. Furthermore, the use of a copper cathode strongly facilitates the reduction since a +0.6 V shift was recorded.

Synthesis and photochromism of 1,2-bis(5-aryl-2-phenylethynylthien-3-yl)hexafluorocyclopentene derivatives

Photochromic dithienylethenes that possess elements of lipid complementarity, and undergo large, photoinduced changes in molecular geometry have been prepared. Further, a regioselective approach has been developed for the preparation of dithienylethenes containing phenylethynyl and various aryl substituents at C2 and C5 of the thiophene moieties, respectively. The prepared photochromic compounds were observed to undergo reversible photoisomerization. Their absorption properties, reaction quantum yields, and photoconversions were determined in n-hexane.

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.

Helically π‐Stacked Conjugated Polymers Bearing Photoresponsive and Chiral Moieties in Side Chains: Reversible Photoisomerization‐Enforced Switching Between Emission and Quenching of Circularly Polarized Fluorescence

AbstractNovel multifunctional conjugated polymers, [poly(p‐phenylene)s and poly(bithienylene‐phenylene)s with (R)‐ and (S)‐configurations], which have fluorescence, chirality, and photoresponsive properties, have been designed and synthesized. The polymers are composed of π‐conjugated main chains, where poly(p‐phenylene) and poly(bithienylene‐phenylene) are fluorescence moieties, and the side chains of the photochromic dithienylethene moiety are linked with chiral alkyl groups. The polymer films exhibit right‐ or left‐handed circularly polarized fluorescence (CPF) and also show reversible quenching and emitting behaviors as a result of photochemical isomerization of the dithienylethene moiety upon irradiation with ultraviolet and visible light. This is the first report realizing the reversible switching of CPF using chirality and photoresponsive properties.

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.

Photochromic molecular wires: Insights from theory

Using an ab initio theoretical spectroscopy approach, we have determined the structures and electronic properties of two molecular wires capped by photochromic dithienylethenes, that have recently been synthesized and characterized. The calculations have been performed with a range-separated hybrid functional (CAM-B3LYP) combined to an extended atomic basis set, and using a solvent model for all computational stages. Not only, we were able to reproduce the position of the measured absorption bands for any closed/open combination, but also to understand why the doubly-closed form is present in the experimental conditions.

Photochromic dithienylethenes with extended π-systems

The syntheses and photochromic properties of six new photochromic dithienylethenes with differently substituted conjugated double bonds at the thiophene units are presented.

Optical control of quantum dot luminescence via photoisomerization of a surface-coordinated, cationic dithienylethene

Photoisomerization of a coordinating, photochromic dithienylethene bearing a pyridine and a methylpyridinium group was investigated as a means to reversibly modulate the luminescence from CdSe-ZnS core-shell quantum dots. Resonance energy transfer and electron transfer are both plausible quenching mechanisms based on an increase in the spectral donor-acceptor overlap and an anodic shift in the reduction potential accompanying the isomerization reaction of the dithienylethene photoswitch. Photochemical degradation of both the quantum dot and photochromic quencher was observed after repeated cycling between the two isomers, suggesting irreversible electron transfer from the quantum dot to the dithienylethene as the dominant luminescence quenching mechanism.

New fast synthesis route for symmetric and asymmetric phenyl-substituted photochromic dithienylethenes bearing functional groups such as alcohols, carboxylic acids, or amines

This Letter describes an efficient three-step synthesis route of symmetric and asymmetric phenyl-substituted photochromic 1,2-dithienylethenes bearing unprotected functional groups (i.e., alcohols, carboxylic acids or amines). These products can be easily obtained by typical Suzuki cross-coupling between photochromic dichlorides and commercial available boronic acids or pinacol esters.

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.

The synthesis and photochromic properties of two bis(phosphine) ligands based on dithienylethene backbone and their oxides, sulfurets and selenides

A phosphor atom was introduced into photochromic dithienylethene and the corresponding dithienylethene bis(phosphine)ligands were obtained by the lithiation of 1,2-bis-(5-chloro-2-methylthien-3-yl) cyclopentene in the presence of n-butyllithium which were then reacted with Ph 2PCl or Cy 2PCl, respectively. The bis(phosphine)ligands were oxidised with H 2O 2, sulfurated by S 8 and selenated by Se and their structures were characterized.

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.