Photochemische Reaktionen. 118. Mitteilung [1] Zur vinylogen β-Spaltung von Enonen. UV.-Bestrahlung von 4-(3',7',7'-Trimethyl-2'-oxabicyclo [3.2.0]hept-3'-en-1'-yl)but-3-en-2-on

Vinylogous β-Cleavage of Enones: UV.-irradiation of 4-(3′,7′,7′-trimethyl-2′-oxabicyclo[3.2.0]hept-3′-ene-1′-yl)but-3-ene-2-on On ¹π,π*-excitation (λ = 254 nm) in acetonitrile (E/Z)- 2 is converted into the isomers 4–9 and undergoes fragmentation yielding 10 ; in methanol (E/Z)- 2 gives 7–10 and is transformed into 11 by incorporation of the solvent. On ¹π,π*-excitation (λ λ?347 nm; benzene-d₆) (E)- 2 is isomerized into (Z)- 2 , which is converted into the isomers 3 and 4 by further irradiation. ¹π,π*-Excitation (λ = 254 nm; acetonitrile) of 4 gives 6 and (E)- 9 , whereas UV.-irradiation (λ = 254 nm; acetonitrile-d₃) of 5 yields (E)- 7 and 8 . On ¹π,π*-excitation (λ = 254 nm; acetonitrile) of (E/Z)- 12 the compounds (E)- 14 and (E)- 15 are obtained.     

Preparation and optical properties of sol–gel materials doped with coumarin molecules

New optical materials containing coumarin (3-(3-(4-(dimethylamino)phenyl)propenoyl)-2H-chromen-2-one) in silica are reproducibly prepared by a sol–gel technique and characterized with UV/Vis and luminescence spectroscopy. The incorporation of the coumarin molecules in the silica gels is monitored with UV/Vis spectroscopy. The coumarin doped gels change their color with time which is attributed to a protonation of the dimethylamino group of the coumarin molecules during aging of the gels and is proved by UV/Vis spectroscopy. The process of protonation of the dimethylamino group is described as a second order reaction. The luminescence spectra of the coumarin doped gels at room temperature also are given.     

Highly substituted azulene dyes as multifunctional NLO and electron-transfer compounds

Two highly substituted azulene derivatives were synthesised by Pd-mediated dimerisation from the corresponding tolan species. One azulene derivative (2) has donor functionalities (dianisylaminophenyl and dianisylamino) in the 1-, 2-, 3- and 6-positions, while the other (1) has donors (dianisylaminophenyl) in the 2- and 6-positions and acceptors (nitrophenyl) in the 1- and 3-positions. Each azulene derivative shows strong bond length alternation in the solid state, determined by X-ray crystal analysis, and an intense CT band around 450-500 nm in its UV/Vis spectrum. The first-order hyperpolarisability of 1 and of 2 was measured by hyper-Rayleigh scattering and is about that of disperse red DR1. Both azulene derivatives show multiple oxidation processes. The intramolecular adiabatic ET behaviour of the mixed valence radical cations of 1 and of 2 was investigated by UV/Vis/NIR spectroelectrochemistry. The intervalence-CT band of 1(+) could be analysed by the Generalised Mulliken-Hush theory, which yields an electronic coupling V=1140 cm(-1) for the optically induced adiabatic hole transfer.     

A Series of Isolable Silanoic Thio‐, Seleno‐, and Telluroesters (LSi(X)OR) with Donor‐Supported SiX Double Bonds (L=β‐Diketiminate; X=S,Se, Te)

The first silicon analogues of carbonic (carboxylic) esters, the silanoic thio‐, seleno‐, and tellurosilylesters 3 (Si?S), 4 (Si?Se), and 5 (Si?Te), were prepared and isolated in crystalline form in high yield. These thermally robust compounds are easily accessible by direct reaction of the stable siloxysilylene L(Si:)OSi(H)L′ 2 (L=HC(CMe)₂[N(aryl)₂], L′=CH[(C?CH₂)‐CMe][N(aryl)]₂; aryl=2,6‐iPr₂C₆H₃) with the respective elemental chalcogen. The novel compounds were fully characterized by methods including multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction analysis. Owing to intramolecular N→Si donor–acceptor support of the Si?X moieties (X=S, Se, Te), these compounds have a classical valence‐bond N⁺–Si–X^? resonance betaine structure. At the same time, they also display a relatively strong nonclassical Si?X π‐bonding interaction between the chalcogen lone‐pair electrons (n_π donor orbitals) and two antibonding Si? N orbitals (σ*_π acceptor orbitals mainly located at silicon), which was shown by IR and UV/Vis spectroscopy. Accordingly, the Si?X bonds in the chalcogenoesters are 7.4 ( 3 ), 6.7 ( 4 ), and 6.9 % ( 5 ) shorter than the corresponding Si? X single bonds and, thus, only a little longer than those in electronically less disturbed Si?X systems (“heavier” ketones).     

Synthesis and photoluminescent properties of 7-N,N-diphenylamino-3- benzoheterocyclic coumarin derivatives

Two new 7-N,N-diphenylamino-3-benzoheterocyclic coumarin derivatives containing electron-transporting benzotriazolyl or benzoxazolyl moiety, 3-(1-benzotriazole)-7-N,N-diphenylaminocoumarin (BTDC) and 3-(2-benzoxazole)-7-N,N-diphenylaminocoumarin (BODC), were synthesized and characterized by element analysis, ¹H NMR and FT-IR spectra. The UV–vis and fluorescence spectra of these coumarin derivatives were investigated. The results show that BTDC and BODC exhibit strong blue and red emissions, respectively, under ultraviolet light excitation. The relationships between the chemical structure and the fluorescence characteristics of the 7-N,N-diphenylamino-3-benzoheterocyclic coumarin derivatives are discussed. It was found that the coumarin derivative will become a high-efficiency emitting material when an amino group is attached in 7-position of the coumarin ring, and 7- strong electron donors can improve the ability of the intramolecular charge transfer of the coumarin molecules.     

Synthesis and studies of new photochromic spiropyrans containing a formylcoumarin fragment

A computer search for new photoactive compounds among indoline spiropyrans of coumarin series was carried out using DFT B3LYP/6-31G(d,p) method. Based on the data obtained, the spiropyrans containing a formylcoumarin fragment annulated to the 2H-pyran ring and possessing photochromic properties were synthesized. The structure and photochromism of these compounds were studied by ¹H NMR, IR, and UV/Vis spectroscopy. The introduction of a formyl group into the coumarin moiety of spiropyrans led to a bathochromic shift of the long wavelength absorption maxima of merocyanine isomers, as well as to a considerable increase in their lifetime.     

A green and efficient synthesis of isoxazol-5(4<Emphasis Type="Italic">H</Emphasis>)-one derivatives in water and a DFT study

A series of 4-arylmethylene-3-methylisoxazol-5(4H)-one derivatives are obtained via treating ethyl acetoacetate, hydroxylamine hydrochloride and variety of aromatic aldehyde compounds in the presence of antimony trichloride as an efficient catalyst in aqueous media. Mild conditions, safe, short reaction times, commercially available catalyst, environmentally friendly, no uses of organic solvent and high yields are remarkable advantages to this process. (Z)-4-(3-hydroxybenzylidene)-3-methylisoxazol-5(4H)-one, (HBIM), is characterized by theoretical (density functional theory) and experimental (IR, ¹H NMR, CV and UV). The structural parameters, vibrational frequencies, molecular electrostatic potential, frontier molecular orbital analysis (HOMO–LUMO), thermodynamic properties and nonlinear optical properties are found and discussed. UV–Vis spectra are recorded in two organic solvents. Thermal stability of HBIM is studied by thermogravimetric analysis. The molecule orbital contributions are studied using the total and partial density of states (TDOS and PDOS).     

Tunable Electronic Properties of a Proton‐Responsive N,N‐Dimethylaminoazobenzene Fullerene (C60) Dyad

A basic N,N‐dimethylaminoazobenzene–fullerene (C₆₀) dyad molecular skeleton is modelled and synthesized. In spite of the myriad use of azobenzene as a photo‐ and electrochromic moiety, the idea presented herein is to adopt a conceptually different path by using it as a bridge in a donor–bridge–acceptor single‐molecular skeleton, connecting the electron acceptor N‐methylfulleropyrrolidine with an electron donor N,N‐dimethylaniline. Addition of trifluoroacetic acid (TFA) results in a drastic colour change of the dyad from yellow to pink in dichloromethane (DCM). The structure of the protonated species are established from electronic spectroscopy and time‐dependent density functional theory (TD‐DFT) calculations. UV/Vis spectroscopic investigations reveal the disappearance of the 409 nm ¹(π→π*) transition with appearance of new features at 520 and 540 nm, attributed to protonated β and α nitrogens, respectively, along with a finite weight of the C₆₀ pyrrolidinic nitrogen. Calculations reveal intermixing of n_(N?N)→π*_(N?N) and charge transfer (CT) transitions in the neutral dyad, whereas, the n_(N?N)→π*_(N?N) transition in the protonated dyad is buried under the dominant ¹(π →π*) feature and is red‐shifted upon Gaussian deconvolution. The experimental binding constants involved in the protonation of N,N‐dimethylanilineazobenzene and the dyad imply an almost equal probability of existence of both α‐ and β‐protonated forms. Larger binding constants for the protonated dyads imply more stable dyad complexes than for the donor counterparts. One of the most significant findings upon protonation resulted in frontier molecular orbital (FMO) switching with the dyad LUMO located on the donor part, evidenced from electrochemical investigations. The appearance of a new peak, prior to the first reduction potential of N‐methylfulleropyrrolidine, clearly indicates location of the first incoming electron on the donor‐centred LUMO of the dyad, corroborated by unrestricted DFT calculations performed on the monoanions of the protonated dyad. The protonation of the basic azo nitrogens thus enables a rational control over the energetics and location of the FMOs, indispensable for electron transport across molecular junctions in realizing futuristic current switching devices.     

Synthesis,characterization and fluorescence behavior of new fluorescent probe phthalocyanines bearing coumarin substituents

In this study, we report a new ligand, 6-hexyloxy-3-[p-(3′,4′-dicyanophenoxy)phenyl]coumarin, and its fluorescent tetrasubstituted phthalocyanines {M[Pc(OBzCou)₄], M = 2H, Zn(II), Co(II); Bz: Benzene}. The effect of the coumarin derivative on the intensity of the fluorescence spectra of the metal-free (H₂Pc) and zinc phthalocyanine (ZnPc) derivatives was investigated. The change of the emission properties of both the coumarin moieties and the phthalocyanine core in the presence of the metal ion and the ring-opening reaction of the coumarin were studied by means of steady-state fluorescence spectroscopy. The radiative decay of the Pcs and the treated coumarin substituents bound to the Pcs was examined. The novel chromogenic compounds were characterized by elemental analysis, ¹H NMR, ¹³C NMR, Maldi-TOF, IR and UV–Vis spectral data. The photophysical properties of the Pcs are extensively affected by their state of aggregation: in particular, dimerization and aggregation result in a remarkable modification of the absorption and emission bands and may induce significant quenching of the usually strong Pc fluorescence. The electronic spectra exhibit a band of coumarin identity together with characteristic Q and B bands of the phthalocyanine core.     

Novel UV-sensitive bis-chalcone derivatives: synthesis and photocrosslinking properties in solution and solid PMMA film

A series of chalcone derivatives in which two chalcone groups are attached by alkyldioxy chains were synthesized and characterized by ¹H NMR, UV–Vis, and Fourier transform infrared (FTIR) spectral analysis. Upon the irradiation of 365-nm UV light, the chalcone groups in the molecules underwent [2π + 2π] photodimerization. The photocrosslinking properties were investigated both in solution and in polymethyl methacrylate (PMMA) solid films on quartz plate. It has been found that the photocrosslinking rates of the compounds depended on the different flexibility of the functional groups, which was determined by the length of the spacer chain between the two chalcone moieties. The longest soft chain containing derivatives has a faster photocrosslinking rate both in solution and in solid film. Irradiated by polarized ultraviolet light (PUV), all of the films doped with bis-chalcone derivatives showed an anisotropic absorption property, which may give a promising application as LC-alignment materials.     

Effects of coumarin substituents on the photophysical properties of newly synthesised phthalocyanine derivatives

In this study, synthesis of new ligands, 8-hydroxy-3-[p-(3′,4′-dicyanophenoxy)-phenyl]coumarin and 8-hexyloxy-3-[p-(3′,4′-dicyanophenoxy)-phenyl]coumarin, and their phthalocyanines, 2,9,16,23-tetrakis[8-hexyloxy-3-(4-oxyphenyl)coumarin]-metal-free and metallophthalocyanines {M[Pc(OBzCou)₄] (M = 2H, Zn(II), Co(II); Bz: benzene; Cou: coumarin)} were synthesised. The novel chromogenic compounds were characterised by elemental analysis: ¹H NMR, ¹³C NMR, MALDI-TOF, IR and UV–vis spectral data. The effect of coumarin substituents on the photophysical properties of metal-free (H₂Pc) and zinc phthalocyanines (ZnPc) derivatives has been examined. Spectrophotometric measurements revealed that coumarin-substituted ZnPc derivatives were in the unaggregated form, whereas those of H₂Pc species were in aggregated form. It means that substitution of coumarin derivative prevents the cluster formation in the presence of zinc ion in the centre of Pc.     

Charge-transfer complexes of pyrimidine Schiff bases with aromatic nitro compounds

Charge-transfer (CT) complexes of pyrimidine Schiff bases, derived from condensation of 2-aminopyrimidine and substituted benzaldehydes, with some aromatic polynitro compounds were prepared and investigated using IR, UV, visible and (1)H NMR spectroscopy. For all solid complexes, the main interaction between the donor and acceptor molecules takes place through the π-π* interaction. Strong and some weak acidic acceptors, in addition interact through proton transfer from the acceptor molecule to the basic centre of the electron donor. Also, an n-π* transition was detected in some complexes.     

Synthesis and fluorescence properties of 7-hydroxy-3-(2-pyridyl)coumarin derivatives

Three coumarin derivatives, 7-hydroxy-3-(2-pyridyl)coumarin (HPC), 7-(4-(5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl)benzyloxy)-3-(2-pyridyl)coumarin (Ox-PC), and 7-(4-(9H-carbazol-9-yl)butoxy)-3-(2-pyridyl)coumarin (Cz-PC), were synthesized and characterized by elemental analysis, ¹H NMR, FT-IR, and UV?Cvis absorption spectra. The fluorescence behaviors of the compounds in methanol solutions and solid states were investigated. HPC exhibits weak green emission, whereas Cz-PC and Ox-PC show strong blue emissions in dilute solutions.     

(Dibenzoylmethanato)boron Difluoride Derivatives Containing Triphenylamine Moieties: A New Type of Electron‐Donor/π‐Acceptor System for Dye‐Sensitized Solar Cells

(Dibenzoylmethanato)boron difluoride derivatives containing triphenylamine moieties were synthesized as a new type of electron‐donor/π‐acceptor system. These new compounds exhibited long‐wavelength absorptions in the UV/Vis spectra, and reversible oxidation and reduction waves in cyclic voltammetry experiments. Their amphoteric redox properties are based on their resonance hybrid forms, in which a positive charge is delocalized on the triphenylamine moieties and a negative charge is localized on the boron atoms. Molecular orbital (MO) calculations indicate that their HOMO and LUMO energies vary with the number of phenylene rings connected to the difluoroboron‐chelating ring. This is useful for optimizing the HOMO and LUMO levels to an iodine redox (I^?/I₃^?) potential and a titanium dioxide conduction band, respectively. Dye‐sensitized solar cells fabricated by using these compounds as dye sensitizers exhibited solar‐to‐electric power conversion efficiencies of 2.7–4.4 % under AM 1.5 solar light.     

One-Pot Synthesis of 1,3,4-Thiadiazin-5-yl-chromen-2-one Derivatives via Three-Component Reaction

An expeditious, one-pot reaction has been described for the preparation of 1,3,4-thiadiazin-5-yl-chromen-2-one derivatives. These compounds were synthesized by the reaction of 3-(2-bromoacetyl)coumarin with thiocarbohydrazide and various carbonyl compounds. The newly synthesized compounds were characterized by infrared, ¹H NMR, and mass spectra.     

Reversible Light‐Driven Polymerization of Polyoxometalate Tethered with Coumarin Molecules

A new photosensitive polyoxometalate (POM) organic–inorganic hybrid compound has been prepared by covalently tethering coumarin moieties onto a Mn–Anderson cluster. This compound has been fully characterized by ¹H NMR, ¹³C NMR, FTIR, and UV/Vis spectroscopy, and ESI‐MS. This organic–inorganic hybrid compound can undergo reversible light‐driven polymerization and this process has been characterized in detail.     

Intramolecular Phototransfer of Protons and the Quenching of Fluorescence of Derivatives of 2-(Coumarinyl-3)-5-(ortho-hydroxyphenyl)-1,3,4-oxadiazole

The spectral-luminescence properties of ortho-hydroxy derivatives of 2-(coumarinyl-3)-5-phenyl-1,3,4-oxadiazole have been studied. It is shown that the basic reason for the decreased quantum yield of emission for the compounds studied is the high-speed phototransfer of a proton (estimated as 109 s^-1). Fluorescence of the products of this reaction (phototautomers) was not observed. It was confirmed by quantum-chemical calculations that the increase in efficiency of nonradiative dissipation of the electron excitation energy in phototautomeric forms of ortho-hydroxycoumarinyloxadiazoles is explained by an increase in intramolecular donor-acceptor interaction on introduction of the coumarin unit into the molecule. As a result of the high efficiency of nonradiative deactivation of the excited state, the ortho-hydroxyderivatives studied have promise as UV photostabilizers in polymeric materials.     

Synthesis,crystal structure and fluorescence properties of two dinuclear zinc(II) complexes incorporating tridentate (NNO) Schiff bases

Reactions of hydrated zinc(II) trifluoroacetate and sodium azide with two tridentate Schiff bases HL¹ (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-chlorophenol) and HL² (2-((E)-(2-(dimethylamino)ethylimino)methyl)-4-bromophenol) under the same reaction conditions yielded two dinuclear isostructural zinc(II) complexes, [Zn(L¹)(N₃)]₂ (1) and [Zn(L²)(N₃)]₂ (2), respectively. The complexes were characterized systematically by elemental analysis, UV–Vis, FT-IR, and ¹H NMR spectroscopic methods. Single-crystal X-ray diffraction studies reveal that each of the dinuclear complexes consists of two crystallographically independent zinc(II) ions connected by double bridging phenoxides. All zinc(II) ions in 1 and 2 are surrounded by similar donor sets and display distorted square–pyramidal coordination geometries. The ligands and complexes reveal intraligand ¹(π → π*) flourescence. The enhancement of the fluorescence intensities for the complexes compared to the ligands indicates their potential to serve as photoactive materials.     

Synthesis and Characterization of Nitrogen and Sulfur Containing 1,4-Naphthoquinones

Abstract

New N,S-disubstituted naphthoquinones were synthesized by reactions of S- and N-nucleophiles with 2,3-dichloro-1,4-naphthoquinone. 2-(Hexadecylthio)-3-(phenylamino)-naphthalene-1,4-dione 5a was synthesized by reaction of 2-chloro-3-(phenylamino)-naphthalene-1,4-dione 3a with hexadecanethiol 4a. The structures of the new synthesized naphthoquinone derivatives were determined by micro analyses and spectroscopic methods (FT-IR, ¹H NMR, ¹³C NMR, MS, and UV/Vis.). Photo- and electrochemical properties of selected compounds were investigated by using fluorescence spectroscopy and the cyclovoltammetry method.