Photodimerization and photooxygenation of 9-vinylcarbazole catalyzed by titanium dioxide and magnesium perchlorate

Photoreaction of 9-vinylcarbazole in acetonitrile in the presence of titanium dioxide and a catalytic amount of magnesium perchlorate gave 3,6-di(9-carbazolyl)-1,2-dioxane as a photooxygenated product via photodimerization of 9-vinylcarbazole.The photoreaction proceeds via an electron transfer mechanism,where magnesium perchlorate accelerated formation of the photo-oxygenated product.

Tetraolefin stereospecific photodimerization and photopolymerization in coordination polymers

In the context of the highly desirable design and preparation of smart materials with adjustable properties based on photoreactive compounds,we report two unique photoreactive coordination polymers(CPs),{[Zn(4-Iba)_(2)(4-tkpvb)]·H_()2O}_(n)(1,4-HIba=4-iodobenzoic acid,4-tkpvb=1,2,4,5-tetrakis(4-pyridylvinyl)benzene)and[Cd(1,4-bdc)(4-tkpvb)]_(n)(2,1,4-H_(2)bdc=1,4-benzenedicarboxylic acid).Depending on the metal ions and auxiliary carboxylate ligands used,the 4-tkpvb ligands in 1 and 2 adopt different mutual arrangements,which facilitate the photodimerization and photopolymerization reactions in single crystal to single crystal(SCSC)transformations.Upon UV light irradiation which results in the dimerization of the 4-tkpvb ligands,the one-dimensional(1D)zigzag chainsof 1 are transformed into a two-dimensional(2D)network of{[Zn(4-Iba)_(2)(bpbtpvcb)_(0.5)]·H_(2)O}_(n)(1a,bpbtpvcb=1,3-bis(4-pyridyl)-2,4-bis(2,4,5-tri(2-(4-pyridyl)vinyl)phenylcyclobutane).Similarly,in the crystals of 2,all 4-tkpvb ligands experience a photopolymerization reaction to form an unprecedented 1D linear organic polymer,poly-1,3-bis(4-pyridyl)-2,5-bis(2-(4-pyridyl)-vinyl)phenyl)cyclobutane(poly-bpbpvpcb).Furthermore,the 2D network of 2 is converted into a three-dimensional(3D)framework of[Cd_(n)(1,4-bdc)_(n)(poly-bpbpvpcb)](2a).This work not only offers a new protocol to selectively synthesize new supramolecular cyclic compounds,but also expands the application of photopolymerization to the synthesis of macromolecules.

Photodimerization-induced transition of helixes to vesicles based on coumarin-12-crown-4

Rational construction of fine-tuning and precisely controllable topological nanostructures based on supramolecular self-assembly system remains a challenge.Herein,coumarin-12-crown-4(1)as a building block was synthesized by one-pot method and showed reversible high stereo-selective photodimerization(anti-head-to-head dimer(anti-HH-1):syn-head-to-head dimer(syn-HH-1)=10.8:1)and photocleavage.Helical nanobelts were formed by the self-assembly of 1 through asymmetrical H-bonds,which were in concordance with the crystal state superstructure.Upon irradiation with 365 nm light,these nanobelts transformed into nanoballs which were constructed by three building blocks.Further,we investigated the photoreaction of 1 and got two pure covalent dimers(anti-HH-1 and syn-HH-1).The anti-HH-1 selfassembled into hollow micro-vesicles.The transformation of superstructures based on photo-controlled multiple blocks shines a light to the research on the relationship between molecules and superstructures.

Photodimerization of azaanthracene derivatives mediated by cucurbit[10]uril

Challenges of achieving efficient photodimerization of azaanthracene derivatives remain due to the low selectivity and slow reaction rate.In this paper,cucurbit[10]uril(CB[10]),with the largest rigid and hydrophobic cavity among CB[n]s,was used to affect the photodimerization reaction of four water-soluble 1-(2-)substituted azaanthracene derivatives(1-4).It revealed that 1-4 could form 1:2 host-guest complexes with CB[10]in aqueous solution.Irradiation of 1 in the presence of 0.5 equiv.of CB[10]selectively produced a head-to-tail(anti-HT)photodimer product.As for 2-4,CB[10]acted as a nanoreactor accelerating their photodimerization reaction in water.Our results suggest that photodimerization of azaanthracene derivatives could be promoted by the CB[10]-based host-guest strategy with high efficiency and selectivity.

Catalyst-free 2+2 Photodimerization of l,4-Bis[2-(4-pyridyl)ethenyl]-benzene in Solution Under Low Power UV Irradiation

Two different kinds of configurations of 1,4-bis[2-(4-pyridyl)etheny 1]-benzene(trans-bpeb and c/5-bpeb)were achieved,and a bpeb dimer was synthesized in dimethyl sulfoxide(DMSO).Compared with the previous work that synthesized the bpeb dimer or polymer in crystal with a template agent needed,the reaction occurred in a solu・tion phase in the present method.A hand-held ultraviolet lamp(365 nm)with the power of 12 W and the Watt density of 0.35 mW/cm2 can realize the photodimerization of bpeb,instead of the high-power mercury lamp in most previous studies.Unlike other 2+2 cycloaddition in liquid state using catalysts even noble metals,no catalysts were required here,which is cost-saving.Only the trans-pbeb can start the cycloaddition and the formation of the close J-aggregations of Zra≪5-pbeb in DMSO is a precondition for explaining the 2+2 photodimerization.The productivity for the 2+2 cycloaddition product was achieved as 55.6%.

Effect of acidity on morphologies and photodimerization kinetics in Langmuir-Blodgett monolayers of styrylquinoline derivatives

The real-time second harmonic generation was employed to investigate the[2＋2]photodimerization of styrylquinoline（SQ） derivatives in Langmuir-Blodgett（LB） monolayers deposited from aqueous subphases with different acidity.It was discovered that the photodimerization rate constant significantly decreased upon the addition of acid.The additional atomic force microscopy measurements revealed that surface morphologies were correlated to the photodimerization kinetics.These experimental results provide direct evidence for the topo-chemical mechanisms of[2＋2]photodimerization in LB films.The current study demonstrates that the intermolecular interactions and aggregation structures play important roles in the photochemical properties at surfaces.

Enhancement of intramolecular excimer formation and photodimerization of anthrylmethyl α,ω-alkanedioates via hydrophobic interactions

The fluorescence spectra and photodimerization of anthrylmethyl a,w-alkanedioates (A-Mn-A) both in organic and in aqueous organic mixed solvents have been studied.In aqueous organic mixed solvents strong intramolecular excimer emission is detected and the quantum yield for the intramolecular photodimerization is significantly greater than those in organic solvents.These observations suggest that hydrophobic interactions force A-Mn-A molecule to self-coil.The ratio of the head-to-head to head-to-tail products in the intramolecular photodimers of A-Mn-A depends on the length of the linking chain.This work presents a successful example of application of hydrophobic interactions to enhancement of large-ring formation.

Synthesis and Crystal Structure of Rctt-1-(2-benzoxazolyl)-2-(4-chlorophenyl)-4-phenyl-3-(4-pyridinyl)cyclobutane

The title compound (C28H21ClN2O, Mr = 436.92) was synthesized by the cross- photodimerization of (E)-2-(2-phenylethenyl)benzoxazole and (E)-4-[2-(4-chlorophenyl)ethenyl]- pyridine in sulfuric acid solution. Its molecular structure has been unequivocally determined by X-ray crystallography. The title compound belongs to triclinic system, space group P?with cell parameters: a = 9.648(3), b = 10.458(4), c = 12.106(4) , a = 89.089(7), b = 75.644(6), g = 68.441(7)? V = 1096.7(7) 3, Z = 2, Dc = 1.323 g/cm3, F(000) = 456 and m(MoKa) = 0.198 mm-1. The final R and wR are 0.0627 and 0.1285, respectively for 1737 observed reflections with I > 2s(I). S = 0.921 and (/s)max = 0.001. The cyclobutane ring has a puckered conformation with four different aryl groups substituted on each carbon atom. The dihedral angles of the cyclobutane ring are 20.2 and 20.6? The bond distances of the cyclobutane ring are 1.541, 1.555, 1.560 and 1.563 ? respectively, which are slightly longer than that of the normal CC single bond. The title compound is the only cross-dimer and its two heteroaryl groups are situated at the trans-1,3 position of the cyclobutane ring, revealing that the cross-photodimerization proceeds in a head-to-tail pattern with high stereo-selectivity.

Synthesis of Hymecromone Derivatives Containing Chiral 1,1'-Bi-2-naphthyl Moiety for Dual-mode Molecular Switch

Some hymecromone derivatives containing chiral 1,1'-bi-2-naphthyl moiety were synthesized and their photodimerizations were investigated. It was found that fluorescence intensity and optical rotation of the new chiral hymecromone derivatives could be regulated by light. This property has potential significance for developing a new type of dual-mode molecular switch.

One-dimensional Coordination Polymers of rctt-1,3-Diphenyl-2,4-bis[2-(5-phenyl)-oxazolyl]cyclobutane with CuCl_2 and CoCl_2

The Cu（Ⅱ） and Co（Ⅱ） supramolecular coordination polymers, [CuCl2（DPO）- （CH3CN）0.5（CH2Cl2）0.5]n （CuDPO, DPO = rctt-1,3-diphenyl-2,4-bis[2-（5-phenyl）oxazolyl]cyclo- butane） and [CoCl2（DPO）]n （CoDPO）, were synthesized and characterized by single-crystal X-ray diffraction method. CuDPO crystallizes in monoclinic, space group P21/n, with a = 11.243（5）, b = 16.070（8）, c = 19.872（9） A, β = 95.678（10）°, Z = 4, V= 3573（3） A3, C35.50H28.50Cl3CuN2.50O2, Mr = 692.00, Dc = 1.287 g/cm3, p = 0.868 mm^-1, F（000） = 1420, S = 1.089, （△/σ）max = 0.069, the final R = 0.0682 and wR = 0.1749. CoDPO is of monoclinie, space group P21/n, with a = 11.396（4）, b = 15.151（5）, c = 17.673（6） A, β = 90.528（6）°, Z = 4, V = 3051.4（17） A3, C34H26Cl2CoN2O2, Mr = 624.40, Dc = 1.359 g/cm3, μ = 0.770 mm^-1, F（000） = 1284, S = 0.981, （△/σ）max = 0.001, the final R = 0.0471 and wR = 0.0961. In each case, the metal cation is coordinated by two C1 anions and two N atoms from oxazole ring of the ligands, which leads to the formation of a one-dimensional polymeric structure. It is found that the cyclobutane ring of coordinated DPO adopts a distorted conformation in the crystal, which is attributed to the increased steric effect between adjacent aryl substituents for the coordination of oxazole ring to metal cation. Thermal gravimetric analysis of the two complexes was also observed.

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Mammalian collagens exhibit weak intrinsic UV fluorescence that depends on the age and previous history of the sample. Post-translational modifications result in additional fluorescent products (e.g. DOPA, dityrosine, and advanced glycation end products (AGE)). UV radiation can cause longer wavelength fluorescent oxidative bands. These alterations can assess the extent of photolysis. We describe the ground- and excited-state oxidative transformations of newly-purchased type I calf skin collagens (samples #092014 and #072012) and a 7-year-old sample (#072005). We compare the effects of UV radiation (mainly 254 nm) and age on the photochemical reaction kinetics and fluorescence spectral distribution of type I calf skin collagen at pH 7.4. The fluorescence spectra of samples #072012 and #092014 were similar but not identical to pure tyrosine, whereas #072005 indicated significant “dark” oxidation at the expense of tyrosine. Fading of oxidized product(s) at 270/360 nm is second-order. Build-up of 325/400 nm (dityrosine) fluorescence is linear with time. Rate parameters r2 and r1 were respectively proportional to second order disappearance of ground state oxidation products and the quasi–first-order photochemical formation of dityrosine. There is a reciprocal relationship between the rates of decrease in the 270/360 nm fluorescence and concomitant increase in 325/400 nm fluorescence. Their relative rates depend on the age of the collagen sample. There is a reciprocal relationship between r1 and r2. This relationship results because both ground state autoxidation and excited state photo-dimerization proceed via a common tyrosyl radical intermediate. Water of hydration appears to play a role in generating tyrosyl radical.

The Interaction(s) between Calf-Skin Hyaluronic Acid (Hyaluronan) and Dermal Type I Calf-Skin Collagen under 254 nm UV Radiation: Ability of Hyaluronan to Alter Qualitative and Quantitative Dimerization of Collagen Tyrosine Residues

The extracellular matrix (ECM) is the non-cellular component present within all tissues and organs, providing not only essential physical scaffolding for the cellular constituents and initiating crucial biochemical and biomechanical cues, required for tissue morphogenesis, differentiation and homeostasis. Roughly divided into two groups, these are 1) the main fibrous ECM proteins: collagens, elastins, fibronectins and laminins. 2) Classification of proteoglycans (PGs) is based on their location and binding. Although many different molecular interactions are possible, they depend on the cells’ condition (i.e. “Normal”, Aged, Wounded/Fibrotic, and cancerous). There is little or no data that addresses the influence of the surrounding ECM on dityrosine formation. As a simpler model, we have replaced total PG with hyaluronan (HA) and have used purified calf-skin collagen tyrosine, which forms dityrosine (A2) under 254 nm UV in buffered solution and (near) physiological temperatures. Our results reveal a complicated temperature dependence involving factors relating to collagen HA structure, and collagen’s photochemical activation parameters.

Pore-Directed Solid-State Selective Photoinduced E–Z Isomerization and Dimerization within Metal–Organic Frameworks

Design and construction of suitable pore microenvironments for selective catalytic reactions of small guest molecules is a major goal for chemists.Herein,we report control of competitive E–Z photoisomerization and photodimerization within porous metal–organic frameworks(MOFs)by fine-tuning the pore microenvironments using different dicarboxylate linkers.MOFs with small pores((E)-X_(MOF_(1))and(E)-X_(MOF_(1))′)favor the photoinduced E–Z isomerization of one encapsulated diaryl alkene substrate while those with large pores(((E)-X)_(2MOF_(2)))prefer the photodimerization of two encapsulated alkene substrates.Both reactions show broad functional group compatibility and proceed stereospecifically in good yields under mild conditions.High local concentration of diaryl alkene ligands and their preorientation within pores facilitate stereoselective dimerization.This pore engineering strategy is applicable to control and create pore microenvironemnts for other photoinduced organic reactions within porous MOFs.

Modulating the properties of quadruple hydrogen bonded supramolecular polymers by photo-cross-linking between the coumarin moieties

Novel linear supramolecular polymers were successfully constructed by self-assemblies of coumarinbridged bifunctional UPy derivative.Benefitting from the photodimerization ability of the coumarin moieties,the linear supramolecular polymers could form the large three-dimensional polymer networks upon UV light irradiation via photo-cross-linking,which provides a viable and alternative procedure to modulate the properties of supramolecular polymers.

Synthesis, structure and photochemical properties of r-1, c-2, t-3, t-4-tetra[2-(5-phenyloxazolyl)]cyclobutane

It was found that the main reason why trans-1, 2-bis [2-(5-phenyloxazolyl) ] ethene (POEOP) has low laser conversion efficiency is that POEOP photodimerized easily with high stereoselectivity. The photodimer r-1, c-2, t-3, t-4-tetra [2-(S-phenyloxazolyl) ] cyclobutane (TPOCB) was synthesized and its crystal structure was determined by X-ray diffraction method. The crystal is monoclinic. The space group is C2/c, with 0 = 2.2289(4), b=0.5406(2), c=2.631 7(7) nm, β=99.38(2)°, Z=4. The molecular cell of TPOCB is centrosymmetric. The dihedral angle between benzene and oxazole ring planes is similar to that of POEOP. It was also found that the photodimerization of POEOP and the photolysis of TPOCB is reversible, increasing the concentration of POEOP is advantageous to photodimerization. In contrast, decreasing the concentration of POEOP is advantageous to photolysis of TPOCB.