Switching of molecular insertion in a cyclic molecule via photo- and thermal isomerization

Two new cyclic ligands were synthesized: a ligand with two trans-azobenzene moieties and one bipyridine moiety, trans(2)-oAB-O13, and a ligand with two trans-azobenzene moieties and two bipyridine moieties, trans(2)-oAB-bpy. Both ligands underwent reversible trans-cis isomerization at the azobenzene moieties. The mole ratios of the trans(2) form:trans-cis form:cis(2) form, evaluated by (1)H NMR spectroscopy of the photostationary states prepared by 1 h illumination, were 0.13:0.27:0.60 (365 nm irradiation) and 0.41:0.47:0.12 (436 nm irradiation) for oAB-O13, and 0.18:0.12:0.70 (365 nm irradiation) and 0.36:0.43:0.21 (436 nm irradiation) for oAB-bpy. When trans(2)-oAB-O13 was mixed with Cu(I), both the bipyridine units and the polyether chains coordinated to the copper center. Addition of a noncyclic bipyridine ligand, trans(2)-oAB-2OH, afforded a bis(bipyridine)copper(I) complex, [Cu(trans(2)-oAB-O13)(trans(2)-oAB-2OH)]BF(4). The bis(bipyridine) ligand, trans(2)-oAB-bpy, formed a 1:1 complex with Cu(I), [Cu(trans(2)-oAB-bpy)]BF(4). [Cu(cis(2)-oAB-bpy)]BF(4) did not undergo the ligand substitution reaction with a noncyclic ligand with two azobenzene moieties and one bipyridine moiety, oAB, whereas its thermal isomerization in the presence of oAB caused the formation of [Cu(trans(2)-oAB-bpy)(trans(2)-oAB)]BF(4), indicating that the isomerization and ligand exchange reactions synchronized via a conformational change of the cyclic ligand.     

Pushing the limit: synthesis, photophysical and DNA binding studies of a NIR-emitting Ru(II)-polypyridyl probe with 'light switch' behaviour

The new Ru(II) polypyridyl complex 1 was synthesised using microwave irradiation from the new polypyridyl ligand 2'DipyTAP', and its photophysical properties, and DNA binding abilities were investigated using various spectroscopic techniques; and 1 was shown to act as a 'NIR molecular light switch' for DNA with an emission window between 680 and 860 nm.     

Microwave Assisted Synthesis of a New Triplet Iridium(III) Pyrazine Complex

A new cyclometalated iridium(III) complex Ir(DPP)₃ (DPP=2,3-diphenylpyrazine) was pre-pared by reaction of DPP with iridium trichloride hydrate under microwave irradiation. The structure of the complex was confirmed by elemental analysis, ¹H NMR, and mass spec-troscopy. The UV-Vis absorption and photoluminescent properties of the complex were investigated. The complex shows strong ¹MLCT (singlet metal to ligand charge-transfer) and ³MLCT (triplet metal to ligand charge-transfer) absorption at 382 and 504 nm, respec-tively. The complex also shows strong photoluminescence at 573 nm at room temperature.These results suggest the complex to be a promising phosphorescent material.     

A Light‐Activated Olefin Metathesis Catalyst Equipped with a Chromatic Orthogonal Self‐Destruct Function

A sulfur‐chelated photolatent ruthenium olefin metathesis catalyst has been equipped with supersilyl protecting groups on the N‐heterocyclic carbene ligand. The silyl groups function as an irreversible chromatic kill switch, thus decomposing the catalyst when it is irradiated with 254 nm UV light. Therefore, different types of olefin metathesis reactions may be started by irradiation with 350 nm UV light and prevented by irradiation with shorter wavelengths. The possibility to induce and impede catalysis just by using light of different frequencies opens the pathway for stereolithographic applications and novel light‐guided chemical sequences.     

Direct DNA photocleavage by a new intercalating dirhodium(II/II) complex: comparison to Rh2(mu-O2CCH3)4

Transition metal complexes possessing the intercalating dppz ligand (dppz = dipyrido[3,2-a:2',3'-c]phenazine) typically bind ds-DNA through intercalation (K(b) approximately 10(5)-10(6) M(-1)), and DNA photocleavage by these complexes with visible light proceeds through the generation of a reactive oxygen species. The DNA binding and photocleavage by [Rh(2)(mu-O(2)CCH(3))(2)(eta(1)-O(2)CCH(3))(CH(3)OH)(dppz)](+) (2) is reported and compared to that of Rh(2)(mu-O(2)CCH(3))(4) (1). Spectral changes and an increase in viscosity provide evidence for the intercalation of 2 to double stranded DNA with K(b) = 1.8 x 10(5) M(-1). DNA photocleavage by 2 is observed upon irradiation with lambda(irr) > 395 nm both in air and deoxygenated solution. DNA photocleavage is not observed for 1 or free dppz ligand under these irradiation conditions. The coupling of a single dppz ligand to a dirhodium(II/II) bimetallic core in 2 provides a means to access oxygen-independent DNA photocleavage with visible light.     

Light-driven interconversion of Pd2L4 cage and mononuclear PdL2 mediated by the isomerization of azobenzene ligand

The lantern-shaped cage Pd₂L₄ and tweezer-like PdL₂ can be synthesized from the trans- and cis-isomer of an azobenzene-containing ligand, respectively, which were characterized by ¹H, ¹³C, ¹H-¹H COSY, DOSY NMR spectroscopies, high-resolution ESI-MS and density function theory (DFT) calculations. The interconversion of Pd₂L₄ and PdL₂ can be achieved via the cis-trans isomerization of the azobenzene unit on the ligand upon alternative irradiation of light 365 nm or 420 nm.     

Water-soluble through-bond energy transfer cassettes for intracellular imaging

A special, water-soluble, fluorescent probe 1 was designed. This consisted of a fluorescein-based component to harvest irradiation at 488 nm and a rhodamine-based part designed to emit it at a significantly longer wavelength. This cassette was used to label an illustrative protein called ACBP. Evidence was accumulated to support the assertion that ACBP-1 bound its native ligand with a binding constant similar to that of the unlabeled protein, and retained its secondary structure (CD). ACBP-1 was imported into cells using the Chariot peptide. Confocal images proved that some ACBP-1 localized into the nucleus (as expected) and, most significantly, it could be visualized more effectively by irradiating at the donor (fluorescein-like) part of the cassette, than the acceptor (rhodamine-like) part. Overall, this study demonstrates that cassettes of this kind can label a protein without significantly perturbing its function or secondary structure and they can be visualized effectively via irradiation of the donor and observation of the acceptor fluorescence.     

Photochemical DNA cleavage by a Berenil analog

Berenil [bis(4-amidinophenyl)1,3-triazene] is a photostable DNA-binding ligand. We describe here the synthesis of N-(3-hydroxypropyl)-Berenil, which in contrast to Berenil is photosensitive to 360 nm irradiation, behaving as a caged diazonium salt. The 4-amidinobenzenediazonium fragment produced by photolysis induces DNA modification and cleavage.     

Light‐Driven Coordination‐Induced Spin‐State Switching: Rational Design of Photodissociable Ligands

The bistability of spin states (e.g., spin crossover) in bulk materials is well investigated and understood. We recently extended spin‐state switching to isolated molecules at room temperature (light‐driven coordination‐induced spin‐state switching, or LD‐CISSS). Whereas bistability and hysteresis in conventional spin‐crossover materials are caused by cooperative effects in the crystal lattice, spin switching in LD‐CISSS is achieved by reversibly changing the coordination number of a metal complex by means of a photochromic ligand that binds in one configuration but dissociates in the other form. We present mathematical proof that the maximum efficiency in property switching by such a photodissociable ligand (PDL) is only dependent on the ratio of the association constants of both configurations. Rational design by using DFT calculations was applied to develop a photoswitchable ligand with a high switching efficiency. The starting point was a nickel–porphyrin as the transition‐metal complex and 3‐phenylazopyridine as the photodissociable ligand. Calculations and experiments were performed in two iterative steps to find a substitution pattern at the phenylazopyridine ligand that provided optimum performance. Following this strategy, we synthesized an improved photodissociable ligand that binds to the Ni–porphyrin with an association constant that is 5.36 times higher in its trans form than in the cis form. The switching efficiency between the diamagnetic and paramagnetic state is efficient as well (72 % paramagnetic Ni–porphyrin after irradiation at 365 nm, 32 % paramagnetic species after irradiation at 440 nm). Potential applications arise from the fact that the LD‐CISSS approach for the first time allows reversible switching of the magnetic susceptibility of a homogeneous solution. Photoswitchable contrast agents for magnetic resonance imaging and light‐controlled magnetic levitation are conceivable applications.     

Photochemically initiated oxidative carbon-carbon bond-cleavage reactivity in chlorodiketonate Ni(II) complexes

Three mononuclear Ni(II) complexes containing a 2-chloro-1,3-diketonate ligand and supported by the 6-Ph(2)TPA chelate, as well as analogues that lack the 2-chloro substituent on the β-diketonate ligand, have been prepared and characterized. Upon irradiation at 350 nm under aerobic conditions, complexes containing the 2-chloro-substituted ligands undergo reactions to generate products resulting from oxidative cleavage, α-cleavage, and radical-derived reactions involving the 2-chloro-1,3-diketonate ligand. Mechanistic studies suggest that the oxidative cleavage reactivity, which leads to the production of carboxylic acids, is a result of the formation of superoxide, which occurs through reaction of reduced nickel complexes with O(2). The presence of the 2-chloro substituent was found to be a prerequisite for oxidative carbon-carbon bond-cleavage reactivity, as complexes lacking this functional group did not undergo these reactions following prolonged irradiation. The approach toward investigating the oxidative reactivity of metal β-diketonate species outlined herein has yielded results of relevance to the proposed mechanistic pathways of metalloenzyme-catalyzed β-diketonate oxidative cleavage reactions.     

Reversible Photochemical Modifications in Dicarbene‐Derived Metallacycles with Coumarin Pendants

Molecular rectangles were obtained from two bis(NHC) ligands, each featuring two terminal coumarin groups and two Ag⁺, Au⁺, or Cu⁺ ions. Upon UV irradiation (λ=365 nm), the dinuclear complexes undergo photochemical modification through a [2+2] cycloaddition reaction of two adjacent coumarin moieties to give a macrocyclic tetra(NHC) ligand. The photodimerization of the coumarin pendants proceeds stereoselectively to give the syn‐head‐head isomers in all cases. Subsequent irradiation at λ=254 nm initiates a photocleavage reaction with reconstitution of the initial dinuclear complexes with coumarin pendants.     

Synthesis and Reactivity of Cationic Boron Complexes Distorted by Pyridine-based Pincer Ligands: Isolation of a Photochemical Hofmann–Martius-type Intermediate

A family of cationic boron complexes was synthesized, using a dianilidopyridine pincer ligand, which imposes in-plane distortion of the geometry at boron towards T-shaped. Reactivity of these cations toward hydride and base was investigated, and the utility of these cations as precursors to a variety of π-conjugated BN heterocycles was demonstrated. 300 nm irradiation of a deprotonated pincer boron complex triggered a C−N cleavage/C−C formation yielding a dearomatized boryl imine, which has a structure akin to the long-proposed intermediate in the photochemical Hofmann–Martius rearrangement. The photo-rearrangement triggers relief of the distortion imposed by the pincer ligand.     

Ruthenium(II) [3 + 2 + 1] mixed ligand complexes: substituent effect on photolability, photooxidation of bases, photocytotoxicity and photonuclease activity

Mixed ligand complexes of ruthenium(II), [Ru(itpy)(bpy)Cl]ClO(4)1, [Ru(itpy)(phen)Cl]ClO(4)2, [Ru(bitpy)(bpy)Cl]ClO(4)3 and [Ru(bitpy)(phen)Cl]ClO(4)4 have been synthesized and characterized. Complex 3 has also been characterized crystallographically. These complexes exhibit photolability of the Ru-Cl bond. Upon irradiation at 440 nm in the presence of nucleosides and nucleotides the complexes exchange chloride for the nucleoside or nucleotide. The photolability of the Ru-Cl bond depends on the nature of the substituent in the tridentate tpy ligand. Photolysis of the complexes in the presence of a nucleoside or nucleotide also produces 8-oxoguanine due to the oxidation of guanine by the excited states of the complexes. These four complexes exhibit photonuclease properties and bring about the cleavage of plasmid DNA when irradiated at 440 nm. These complexes have been found to be toxic towards NIH 3T3 cells under photolytic conditions.     

Photoswitchable electrochemical behaviour of a [FeFe] hydrogenase model with a dithienylethene derivative

A diiron dithiolate complex 1o with a dithienylethene (DTE) phosphine ligand has been elaborately designed and fully investigated by spectroscopic and DFT computational studies. Upon irradiation with UV light, the DTE moiety in complex 1o undergoes an excellent photocyclization reaction to attain ring-closed state 1c in high yield (>95%), accompanied by a colour change from orange to deep blue. On the other hand, upon irradiation with visible light (>460 nm), ring-closed form 1c in CH(3)CN solution reverts perfectly into ring-open form 1o. Both 1o and 1c were characterised by IR, (1)H, (31)P, (19)F NMR and electrochemical spectroscopy. The electrochemical behaviours of both the open and closed forms were investigated by cyclic voltammetry. Upon photocyclization reaction, a 290 mV (from -2.29 V to -2.00 V) positive shift is induced in the potential of electrochemical catalytic proton reduction, due to the electron-withdrawing effect of the ring-closed DTE moiety. Consequently, complex 1 can reversibly photoswitch the potential of proton reduction on the [FeFe] moiety.     

Wavelength-dependent photofragmentation of a mixed-ligand cyclometalated platinum(II) coordination compound in a molecular beam

The photofragmentation of (3-Me-4',6'-dfppy)Pt(dpm) (dfppy = difluorophenylpyridinato; dpm = dipivaloylmethyl or 2,2,6,6,-tetramethyl-3,5-heptanedionato- O, O) in a molecular beam is reported. Time-of-flight mass spectra (TOF-MS) and resonance-enhanced multiphoton ionization (REMPI) data are presented and discussed. The dissociation patterns are strongly wavelength-dependent. With 355 nm excitation, the heaviest mass platinum-containing fragments are Pt(+) and diatomic PtC(+). The formation of PtC(+) is the result of an intramolecular rearrangement on the ligand. During irradiation with 410-500 nm light, the fragmentation pattern changes such that the parent ion and platinum-containing fragments of the parent are formed in abundant yield. The (3-Me-4',6'-dfppy) ligand remains intact and coordinated to platinum, but coordinated (dpm) successively breaks apart. A spin-forbidden charge-transfer absorption band centered at around 460 nm plays an important role in the gas-phase photoexcitation of the parent molecule; it is observed in the REMPI spectrum of the parent ion.     

Synthesis and Reactivity of Cationic Boron Complexes Distorted by Pyridine‐based Pincer Ligands: Isolation of a Photochemical Hofmann–Martius‐type Intermediate

A family of cationic boron complexes was synthesized, using a dianilidopyridine pincer ligand, which imposes in‐plane distortion of the geometry at boron towards T‐shaped. Reactivity of these cations toward hydride and base was investigated, and the utility of these cations as precursors to a variety of π‐conjugated BN heterocycles was demonstrated. 300 nm irradiation of a deprotonated pincer boron complex triggered a C?N cleavage/C?C formation yielding a dearomatized boryl imine, which has a structure akin to the long‐proposed intermediate in the photochemical Hofmann–Martius rearrangement. The photo‐rearrangement triggers relief of the distortion imposed by the pincer ligand.     

N,N,O,O-四齿配体-钯(Ⅱ)配合物的生成反应热动力学及在Suzuki反应中的催化活性

合成了新型双齿配体5-羟基-1-(6-氯吡啶-2-基)-1H-吡唑-3-羧酸甲酯及其钯配合物并进行了表征. 通过微热量计测定计算了配合物形成的热力学和动力学参数, 计算结果显示, 该配合物极易形成, 在空气和溶液中稳定, 可以用作Suzuki反应的催化剂. 使用1%(摩尔分数)的催化剂, 以2倍量的氢氧化钾为碱, 乙醇-水为溶剂, 在120℃微波加热2 min, 使具有不同电子和空间效应的溴代芳烃和苯硼酸或对甲氧基苯硼酸反应, 偶联产物的分离产率可以达到80.7%~95.9%. 氯代芳烃也以合适的产率得到偶联产物.     

Ruthenium(II) complexes of 1,12-diazaperylene and their interactions with DNA

Four complexes of the ligand 1,12-diazaperylene (DAP) have been prepared, [Ru(bpy)n(DAP)(3-n)]2+ where n = 0-2 and [Ru(DAP)3]2+. The [Ru(DAP)3]2+ complex was characterized by X-ray analysis and was found to exhibit the expected propeller-like structure with significant intermolecular pi-stacking interactions. The three Ru(II) complexes showed self-consistent optoelectronic properties with similar ligand-centered pi-pi* absorptions in the range of 333-468 nm and MLCT bands associated with the DAP which increased in intensity and decreased in energy as the number of DAP ligands varied from 1 to 3. Hypochromicity and viscosity changes were observed that were consistent with DAP intercalation into DNA, and binding constants were measured in the range of 1.4-1.6 x 10(6) M(-1) for the mixed ligand complexes. Furthermore, the complex [Ru(bpy)2(DAP)]2+ was found to photocleave plasmid DNA upon irradiation with visible light.     

α-环糊精修饰型香豆素的设计合成

以环氧氯丙烷为桥接,利用水溶性α-环糊精(α-CD)进行7-羟基-4-甲基香豆素的功能化修饰,得到新型α-环糊精修饰型香豆素衍生物(α-CD-C).用傅里叶变换红外(FT-IR)光谱、氢核磁共振(1H NMR)、液质联用(LC-MS)等对该香豆素衍生物进行了结构表征.紫外光二聚实验表明,该α-环糊精修饰型香豆素可在365 nm光照下进行光二聚反应,且可在随后的254 nm光照下进行解二聚反应;同时通过比较该交替光照下的光二聚反应程度,可知该光二聚反应仅是部分可逆的.     

四齿配体[Ru(iph)(L)2]2+ (L=cpy,mpy, npy)配合物的结构和光谱特征

采用密度泛函的B3LYP和UB3LYP方法分别优化了一系列[Ru(iph)(L)₂]²⁺ (L=cpy (1), mpy (2), npy (3); 其中iph为2,9-双(1′-甲基-2′-咪唑)-1,10-邻二氮杂菲, cpy为4-氰基嘧啶, mpy为4-甲基嘧啶, npy为4-氮二甲基嘧啶)配合物的基态和激发态结构. 利用含时密度泛函理论(TD-DFT)方法, 结合极化连续介质(PCM)模型计算了它们在丙酮溶液中的吸收和发射光谱. 研究结果表明: 优化得到的几何结构参数和相应的实验值符合得非常好. 1和2的最高占据分子轨道主要由金属的d轨道和iph配体的π轨道构成, 但是3主要占据在npy配体上, 而它们的最低空轨道主要由iph配体的π反键轨道占据. 因此, 1和2的最低能吸收和发射属于金属到配体(MLCT)和配体内部(ILCT)的电荷转移跃迁, 而3属于两个配体之间的电荷转移(LLCT)跃迁. 三个配合物的最低能吸收分别在509 nm (1), 527 nm (2)和563 nm (3), 其磷光发射分别在683 nm (1), 852 nm (2)和757 nm (3). 这显示出通过调节L配体的π电子给予能力可以改变最低能吸收和发射的跃迁性质和发光颜色.