Showing papers in "Molecular Crystals and Liquid Crystals in 2005"
TL;DR: In this article, a real-time microbial sensor based on a lyotropic chromonic liquid crystal (LCLC) was proposed to detect and amplify the presence of immune complexes.
Abstract: We describe director distortions in the nematic liquid crystal (LC) caused by a spherical particle with tangential surface orientation of the director and show that light transmittance through the distorted region is a steep function of the particle's size. The effect allows us to propose a real-time microbial sensor based on a lyotropic chromonic LC (LCLC) that detects and amplifies the presence of immune complexes. A cassette is filled with LCLC, antibody, and antigen-bearing particles. Small and isolated particles cause no macroscopic distortions of the uniformly aligned LCLC. Upon antibody-antigen binding, the growing immune complexes disrupt the uniformity of the director and cause detectable optical transmittance between crossed polarizers.
111 citations
TL;DR: In this article, the authors found that various optical dyes inserted into the double helix of DNA molecules rendered active optical waveguide materials with excellent nonlinear optical properties, including photochromic dyes, nonlinear optic chromophores, two photon dyes and rare earth compounds.
Abstract: Purified deoxyribonucleic acid (DNA) derived from salmon and scallop sperm has demonstrated excellent passive and active optical properties. Characterization of the optical and electromagnetic properties of DNA suggests suitability for photonic applications. One of interesting features of DNA we discovered was an intercalation of aromatic compounds into stacked layers within the double helix of DNA molecules. We found that various optical dyes inserted into the double helix of DNA molecules rendered active optical waveguide materials with excellent nonlinear optical properties. Our research included the investigation of DNA for use as an optical waveguide material as well as intercalation of fluorescent dyes, photochromic dyes, nonlinear optic chromophores, two photon dyes and rare earth compounds into DNA for use as a nonlinear optical material.
94 citations
TL;DR: In this paper, the dependence of the lasing threshold on dye concentration and sample thickness was studied and it was shown that a mirrorless lasing system with dye-doped and pure cholesteric liquid crystals can operate efficiently in the range of dye concentrations of 0.3-2.4% with sample thickness of 10-50μm.
Abstract: Cholesteric liquid crystals (CLCs) are one dimensional photonic band-gap materials. Due to distributed feedback, low threshold mirrorless lasing can occur in dye-doped and pure CLCs. In order to optimize the lasing conditions, we have studied the dependence of the lasing threshold on dye concentration and sample thickness. In particular, we have studied dye concentrations in the range of 0.1–3.0 wt%, and cell thicknesses are in the range of 5–50 μm. We have found that the system has a shallow lasing threshold minimum and can operate efficiently in the range of dye concentrations of 0.3–2.4 wt% and sample thicknesses of 10–50 μm. We discuss the physical processes responsible for the observed behaviour.
62 citations
TL;DR: In this paper, a biotinylated diheteroarylethene derivative was bound to quantum dots bearing conjugated streptavidin, leading to an intensity decrease as a consequence of energy transfer to the closed form of the acceptor.
Abstract: The reversible modulation of the emission of CdSe/ZnS semiconductor nanocrystals (quantum dots) was achieved by binding photochromic diheteroarylethenes and switchable acceptors for fluorescence resonance energy transfer. A biotinylated diheteroarylethene derivative was bound to quantum dots bearing conjugated streptavidin, leading to an intensity decrease as a consequence of energy transfer to the closed form of the acceptor. Interconversion between the open and closed forms by irradiation with 365 and 546 nm light enabled deactivation and activation, respectively, of the FRET process with a corresponding modulation of quantum dot emission, observed both in solution and by sequential wide-field imaging.
58 citations
TL;DR: In this article, photo-polymerization of liquid crystalline di-acrylates is a very versatile method to produce homogeneously aligned polymer films, and the orientation of the liquid crystals and hence the anisotropic optical properties of the films are frozen in by the photopolymerisation process.
Abstract: Photo-polymerisation of liquid crystalline di-acrylates is a very versatile method to produce homogeneously aligned polymer films. The orientation of the liquid crystals and hence the anisotropic optical properties of the films are frozen in by the photo-polymerisation process. Homogeneously aligned nematic liquid crystals form birefringent films that find application as retarders, while splayed nematic liquid crystalline mixtures form angle dependent birefringent films that find application as wide viewing angle foils. In addition, cholesteric liquid crystals form reflecting films that can be used as colour filters or polarisers and smectic liquid crystals form highly ordered films that find application as polarisers. Moreover, modulating the light during the manufacturing process either in lateral or in-depth direction of the film can create complex structures not attainable with liquid crystalline polymers. All these films are mechanically, thermally and chemically stable and therefore very su...
54 citations
TL;DR: In this article, the de Vries model of SmA* phases as well as the dimers creation process were used to analyze the optical tilt Θo angle in comparison with a tilt angle obtained from X-ray measurements.
Abstract: The compounds from the fluorinated nF6B (n = 1,2,3,4,5,6,7) homologous series were investigated by means of optical, electrooptical, refractometrical, dielectric, densytometric, X-ray and IR spectroscopy methods. For some compounds being a subject of investigations a computer simulation of molecular properties were done. In our opinion high value of optical tilt Θo angle in comparison with a tilt angle obtained from X-ray measurements can be interpreted in terms of de Vries model of SmA* phases as well as of dimers creation process.
35 citations
TL;DR: The pi-halogen dimer (PHD) interaction is a new intermolecular packing motif discovered in certain crystalline diquinoline compounds as discussed by the authors, which consists of one aromatic offset face-face (OFF) interaction, and four aromatic pi- halogen interactions, and provides a compact building block for the self-assembly of lattice inclusion compounds.
Abstract: The pi – halogen dimer (PHD) interaction is a new type of intermolecular packing motif discovered in certain crystalline diquinoline compounds. It consists of a combination of one aromatic offset face-face (OFF) interaction, and four aromatic pi – halogen interactions, and provides a compact building block for the self-assembly of lattice inclusion compounds. This article reviews the current state of knowledge about this new solid-state construction motif.
30 citations
TL;DR: In this paper, three photosensitive cholesteric liquid crystal mixtures have been investigated as UV sensors, each of which is sensitive to a well definite part of the solar UV radiation spectrum.
Abstract: Three photosensitive cholesteric liquid crystal mixtures have been investigated as UV sensors. Each of them is sensitive to a well definite part of the solar UV radiation spectrum, the UV A or the UV B or the UV C range, with suitable absorption spectra. The photosensitive elements in the mixtures are either photoisomerizable nematic hosts or photoisomerizable optically active dopants. The selective reflection peaks of these cholesteric mixtures are in the visible part of the light spectrum. The UV exposure changes the cholesteric pitch and hence the position of the selective reflection peak. The consequence is that the colour reflected by each mixture varies under influence of the UV and it can be used as an indicator of the UV exposure itself. We present the mechanisms of the observed effects and possible application features.
30 citations
TL;DR: In this article, a series of chalcone derivatives with a general formula of CH3CnH2nCOOC6H4CH:CHCOC 6H4 were well synthesized and crystallized from organic solution.
Abstract: A series of new chalcone derivatives with a general formula of CH3CnH2nCOOC6H4CH:CHCOC6H4 where n = 10, 12, 14, and 16 were well synthesized and crystallized from organic solution. The physical properties as well as the chemical formulations of these compounds were determined by the microanalysis and spectroscopic methods (FTIR, and 1H and 13C NMR). Crystal structure of CH3C10H20COOC6H4CH:CHCOC6H4 was determined by single-crystal X-ray diffraction analysis. The space group of this crystal is triclinic with a = 5.8570(3) A, b = 8.5640(5) A, c = 24.1592(12) A, V = 1175.82(11) A3, and Z = 2, and its structure was refined to R(F) = 0.055 and ωR(F 2 ) = 0.161. The elongated terminal alkyl chain is fully stretched in solid phase. Phase-transition temperatures and the thermal parameters were obtained from differential scanning calorimetry (DSC). The texture observation was carried out with a polarizing optical microscope (POM) over heating and cooling cycles. All of the title compounds except undecylcar...
27 citations
TL;DR: In this article, 3,3,3′-Di(9-(4-butylphenyl)carbazyl) and 3, 3′-di(9-ethyl carbazyl)-based hydrazones were synthesized by a multi-step synthetic route including oxidative dimerization of 9-(4,butyl) carbazole and 9-ethylcarbazole, formylation of the dimmers obtained and the reactions of the formyl derivatives with different hydrazines.
Abstract: 3,3′-Di(9-(4-butylphenyl)carbazyl) and 3,3′-di(9-ethylcarbazyl)-based hydrazones were synthesized by the multi-step synthetic route including oxidative dimerization of 9-(4-butylphenyl)carbazole and 9-ethylcarbazole, formylation of the dimmers obtained and the reactions of the formyl derivatives with different hydrazines. The chemical structure of the compounds was confirmed by 1HNMR, IR and mass spectroscopy. The hydrazones synthesized form stable glasses with the glass transition temperatures exceeding 140°C. The values of ionisation potentials measured by electron photoemission technique are in the range of 5,21–5,4 eV. The hole drift mobilities in the films of the 50% solid solutions of the hydrazones in bisphenol Z polycarbonate established by the xerographic time-of-flight technique exceed 10−5 cm2/Vs at high electric fields.
26 citations
TL;DR: In this article, two types of cross-linked liquid-crystalline polymer films were prepared: monodomain films and polydomains films, and exposure of the polydomain films to UV linearly polarized light led to bending of the films always along the polarization direction of the actinic light.
Abstract: Cross-linked liquid-crystalline polymer films were prepared by polymerization of mixtures containing azobenzene monomers and cross-linkers with azobenzene moieties. Two types of the cross-linked liquid-crystalline polymer films were prepared: monodomain films and polydomains films. Photoirradiation of the monodomain films with UV linearly polarized light (LPL) gave rise to bending of the films toward actinic light along the polarization direction, when the light polarization was parallel to the rubbing direction. When the two directions were perpendicular to each other, the bending was isotropic without a preferential direction. On the other hand, exposure of the polydomain films to UV LPL led to bending of the films always along the polarization direction of the actinic light. This means that one can induce bending of the film along any direction precisely by choosing the polarization direction of the actinic light.
TL;DR: In this paper, the authors discuss the analysis and interpretation of intermolecular space in crystals and provide some principles for the analysis, interpretation, and management of all possible intermoles interactions and their energies.
Abstract: Control of the assembly of molecules in the crystalline state requires management of all possible intermolecular interactions, and their energies. Any one molecule is surrounded by and interacts with parts of the surface of several others, and it is the balance of all the intermolecular interaction energies that determines the lattice enthalpy, and therefore the product structure. In this context of competition between different intermolecular contacts, simplification occurs when intermolecular motifs operate in concert, as in multiple aryl embraces. Structural hierarchies of extended embrace motifs occur in crystals, analogous to the secondary ⇒ tertiary ⇒ quaternary construction of biological macromolecules. Some principles for the analysis and interpretation of intermolecular space in crystals are discussed. Richly abundant data on the packing of molecules in crystals provides the basis for the description of intermolecular motifs, but this data is only geometrical. A different property, inter...
TL;DR: In this paper, the authors studied numerically the interaction between particles in a nematic liquid crystal mediated by its elastic distortions with the aid of the Landau-de Gennes continuum theory.
Abstract: We study numerically the interaction between particles in a nematic liquid crystal mediated by its elastic distortions with the aid of the Landau-de Gennes continuum theory. We consider the cases where two particles impose rigid normal anchoring on their surfaces and are accompanied by a hyperbolic hedgehog defect. As a function of the distance between the centers of the particles D, we evaluate the force f acting on the particles by integrating the stress tensor. The result is well described by a power law f ∝ D −x . When the “dipoles”, composed of a particle and a hyperbolic hedgehog, are in parallel directions, the interaction is attractive and the exponent is x ≃ 4, consistent with the experimental observations together with the theoretical expectation of the dipole-dipole interaction. For antiparallel dipoles, repulsive interaction is observed and x ≃ 3.6, slightly stronger than the dipole-dipole interaction.
TL;DR: The electroluminescence of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) under DC magnetic field has been investigated experimentally and analyzed theoretically.
Abstract: The electroluminescence (EL) of poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) under DC magnetic field has been investigated experimentally and analyzed theoretically. We have estimated the lifetime of intermediate polaron pairs and relation between rate constants of recombination of triplet and singlet polaron pairs from the changes of the EL intensity caused by the DC magnetic field. The short lifetime of the polaron pairs (about 2 × 10−10s) in MEH-PPV has been discussed by taking the intersystem crossing in polaron pairs into consideration.
TL;DR: In this paper, the authors investigated the relationship between the surface property of rubbed polyimides and the variation of pretilt angle according to the side chain and main chain structures of the polyimide.
Abstract: We have investigated the relationship between the surface property of rubbed polyimides and the variation of pretilt angle according to the side chain and main chain structures. We calculated the surface free energy of synthesized polyimide surface by measuring the contact angles of distilled water and methylene iodide on the rubbed polyimide surface. Consequently, we found that pretilt angles on rubbed polyimides changed according to the side chain and main chain structures of the polyimide. Our calculations show that LC pretilt angles of polyimide films with a liquid crystal structure as a side chain were approximately 90° when a linear and rigid polyimide main chain and a side chain of suitable length were employed.
TL;DR: In this article, the surface structure and organization of the polymer films were investigated by measurements of the static contact angle with several interrogating liquids and by X-ray photoelectron spectroscopy at different take-off angles.
Abstract: We prepared several triblock copolymers of the A‒B‒C and A–C–B types composed of hydrophobic polystyrene (A), hydrophobic/lipophobic fluorinated polystyrene (B), and hydrophilic PEG-modified polystyrene (C) blocks with greatly varied degrees of polymerization. The resulting surface structure and organization of the polymer films were investigated by measurements of the static contact angle with several interrogating liquids and by X-ray photoelectron spectroscopy at different take-off angles. The contact angle values were also used to evaluate the film surface tensions, following two fundamentally different approaches. The low surface energies found for any of the triblock copolymers were attributed to the pronounced hydrophobicity and lipophobicity of the outermost surface caused by the preferential segregation of the fluorinated block regardless of the distinctly different macromolecular architectures of the triblock copolymers.
TL;DR: In this article, the influence of the bridging group between the mesogenic group and the terminal position on liquid-crystalline behavior was investigated, and mesogens with only the isoxazole group showed better thermal properties than those with isoxozoles and tetrazoles.
Abstract: The influence of the bridging group between the mesogenic group and the terminal position on liquid-crystalline behavior was investigated. Two liquid-crystalline series containing pentagonal heterocycles were synthesized for this purpose. The liquid-crystal phase of mesogens with the isoxazole group was more stable than that of those with isoxazole and tetrazole groups in the same molecule. The mesogens with only the isoxazole group showed better thermal properties than those with isoxazoles and tetrazoles. Nematic and smectic phases were observed. The mesophase sequences of the materials were investigated by polarization microscopy and DSC (Differential Scanning Calorimetry).
TL;DR: A novel azobenzene-based photochromic amorphous molecular material, tris[4-(phenylazo)phenyl]amine (TPAPA), was designed and synthesized.
Abstract: A novel azobenzene-based photochromic amorphous molecular material, tris[4-(phenylazo)phenyl]amine (TPAPA), was designed and synthesized. TPAPA was found to readily form an amorphous glass with a glass-transition temperature of 67°C and to exhibit photochromism as amorphous film. Irradiation of amorphous film of TPAPA with two coherent Ar+ laser beams led to the formation of surface relief grating with a diffraction efficiency of 2 ≈ 3% and a modulation depth of ca. 100 nm.
TL;DR: In this article, the effect of a hydrodynamic flow on the orientational configuration of a nematic liquid crystal around a spherical particle imposing rigid normal anchoring was studied, and it was shown that strong elastic deformation by the flow is expected.
Abstract: We study the effect of a hydrodynamic flow on the orientational configuration of a nematic liquid crystal around a spherical particle imposing rigid normal anchoring. We discuss the cases of large Ericksen numbers (characterizing the ratio of viscous force to the elastic force), where strong elastic deformation by the flow is expected. We assume the Stokes flow profile and deal with a simplified dynamic equation of the orientational order parameter of a second-rank tensor Q αβ. We consider the cases where a particle accompanying a hyperbolic hedgehog or a Saturn ring is subjected to a flow along the axis of rotational symmetry. In both cases the orientation profiles exhibit considerable deformation by a flow.
TL;DR: In this paper, the thermophysical properties of hexanethiolate capped gold nanoparticles and discotic liquid crystals were investigated using polarizing optical microscopy, differential scanning calorimetry and DC conductivity.
Abstract: Several mixtures of hexanethiolate capped gold nanoparticles and discotic liquid crystals were prepared. The thermophysical properties of these mixtures were investigated using polarizing optical microscopy, differential scanning calorimetry and DC conductivity. Formation of columnar mesophase and about 250 times enhancement in the DC conductivity indicate inclusion of gold nanoparticles into the matrix of triphenylene based discotic liquid crystals.
TL;DR: In this paper, the half-life and absorption maxima of the colored betaines 2′a-g were determined for pyrazoline based photochromes using laser flash spectroscopy.
Abstract: Spirotetrahydroindolizines (THIs) 1a-g and Spirotetrahydroazafluorenes (THF) 2a-g were previously synthesized. The high reaction rate of the thermal 1,5-electrocyclization results in the half-lives of the colored betaines 2′a-g range from 3.9 to 5.4 ns, thus showing the existence of the shortest lived colored form observed so far for pyrazoline based photochromes. However, laser flash spectroscopy was successfully used for the determination of both the half-life and absorption maxima of the colored betaines 2′a-g. Time resolved transient spectroscopy shows the geometry of the betaines 2′a-g to be related to one of the two detectable intermediates 1′a-g or 1′′a-g.
TL;DR: In this article, a series of azobenzene containing polymers with varying molecular weight was investigated for surface relief grating formation, and the modulation depth of the gratings as measured by AFM decreases with increasing molecular weight, however, the effect was much smaller than expected.
Abstract: Surface relief grating formation was investigated for a series of azobenzene containing polymers with varying molecular weight. The polymers were obtained by a combination of an atom transfer radical polymerization of trimethylsilylethyl methacrylate and subsequent polymeranalogous introduction of the azobenzene chromophore. Irradiation of the polymers with interfering polarized laser beams resulted in the formation of surface relief gratings. The modulation depth of the gratings as measured by AFM decreases with increasing molecular weight, however, the effect is much smaller than expected.
TL;DR: In this article, a series of thermotropic liquid-crystalline folate derivatives with hierarchical chiral structures at the oligo (glutamic acid) parts were presented.
Abstract: We have prepared a series of thermotropic liquid-crystalline folate derivatives which have hierarchical chiral structures at the oligo (glutamic acid) parts. The complexes of the folic acids with sodium salts show hexagonal columnar and Pm3n cubic phases. The addition of the salts induces supramolecular chirality in the columnar and cubic phases. Tuning of molecular chirality at the oligo(glutamic acid) moieties greatly affects their supramolecular chiral structures.
TL;DR: In this paper, the nucleophilic addition of the substituted isoquinoline derivatives to diacetyl spirocyclopropene 1 in dry ether at −20°C under nitrogen atmosphere for 3h, which undergo ring opening the corresponding betaines 3′,3′-diacetyl spirtertrahydroindolizines (THIs) 3a−g were synthesized in low yield via the nucleophysical addition of these derivatives to the diacetyll spirocycline.
Abstract: Seven novel 2′,3′-diacetyl spirotertrahydroindolizines (THIs) 3a–g were synthesized in low yield via the nucleophilic addition of the substituted isoquinoline derivatives 2a–g to diacetyl spirocyclopropene 1 in dry ether at − 20°C under nitrogen atmosphere for 3 h, which undergo ring opening the corresponding betaines 3′′′a–g through betaine 3′a–g and 3″a–g as intermediates after irradiation with UV-light. The serious decomposition of these products during purification process was moderately prevented by using flash chromatography after many trials. In situ hydrazinolysis of THIs 3a–g with hydrazine in ethanol at − 40°C afforded a novel type of cis-fixed pyridazinopyrrolo[1,2-b]isoquinolines 4a–g in moderate yield.
TL;DR: In this article, a variety of superstructures are generated in the chiral smectic phases, including ferrielectric and antiferroelectric phases, a twist grain boundary phase and the variants, such as smectric blue and Smectic Q phases, and mysterious isotropic phases exhibiting an anomalous electric-field induced phase transition.
Abstract: Molecular design producing a strong chiral effect has been proposed and dichiral twin and monomeric materials have been prepared systematically based on this concept. A variety of superstructures are generated in the chiral smectic phases, including ferrielectric and antiferroelectric phases, a twist grain boundary phase and the variants, such as smectic blue and smectic Q phases, and mysterious isotropic phases exhibiting an anomalous electric-field induced phase transition.
TL;DR: The frequency of dipole relaxation of liquid crystal (LC) layer at LC- solid interface, fr, is shown to be in full correlation with the polar anchoring energy W p ; the increase of W p is accompanied with the decrease of f r. This correlation is established by the use of the aligning polyimide layers treated with different methods.
Abstract: The frequency of dipole relaxation of liquid crystal (LC) layer at LC- solid interface, fr, is shown to be in full correlation with the polar anchoring energy W p ; the increase of W p is accompanied with the decrease of f r . This correlation is established by the use of the aligning polyimide layers treated with different methods. The anchoring energy increases and the relaxation frequency decreases in the following sequence of processes: rubbing–photoalignment–plasma beam alignment. The correlation between W p and f r is an evidence of strong contribution of dipole-to-dipole interaction at the LC-substrate interface to polar anchoring of LC. Based on this correlation new method of polar anchoring measurement can be developed.
TL;DR: The behavior of the 2H NMR linewidth throughout the whole mesophasic range of the ferroelectric liquid crystal 1-methylheptyl 4′-(4-decyloxybenzoyloxy) biphenyl-4-carboxylate (10B1M7) is discussed in this paper.
Abstract: The behaviour of the 2H NMR line-width throughout the whole mesophasic range of the ferroelectric liquid crystal “1-methylheptyl 4′-(4″-n-decyloxybenzoyloxy) biphenyl-4-carboxylate” (10B1M7) is here reported and discussed. Static Fringe Field NMR Diffusometry measurements from the isotropic to the anticlinic phase have been performed leading to a significant result concerning the tumbling diffusional coefficient (D⊥). These results have been compared to X-Ray measurements and 2H NMR line-widths in order to explain the peculiar behaviour occurring at the transition between the ferroelectric (FLC) and the antiferroelectric (AFLC) liquid crystalline phases.
TL;DR: In this paper, a femtosecond transient absorption spectroscopy was applied to the dynamics of different substituted fulgides in a polyamide (PMMA) environment as compared to liquid solution (toluene).
Abstract: The dynamics of fulgide photoswitches has been investigated applying femtosecond transient absorption spectroscopy. The switching performance of differently substituted fulgides is equally improved in polymer (PMMA) environment as compared to liquid solution (toluene). In the polymer a single pathway for the ring-closure reaction, i.e., without the intermediate observed in toluene, allows for sub-picosecond reaction times. The ring-opening (on-switching) reaction in the donor-acceptor substituted energy-transfer system occurs on ps time scale.
TL;DR: In this paper, two liquid crystalline partially fluorinated compounds exhibiting paraelectric, ferroelectric and antiferroelectric phases have been studied by dielectric spectroscopy and spontaneous polarization measurements.
Abstract: Two liquid crystalline partially fluorinated compounds: (S)–(+)–4-(1-metyloheptyloxycarbonylphenyl) 4′-(6-perfluorobutanoyloxyhex-1-oxy) biphenyl-4-carboxylate, in short MHPP(9F)HBC and (S)–(+)-4-(1-metyloheptyloxy-carbonylbiphenyl) 4′-(6-perfluorobutanoyloxyhex-1-oxy) benzoate, in short P(9F)HPMHBC, exhibiting paraelectric, ferroelectric and antiferroelectric phases have been studied by dielectric spectroscopy and spontaneous polarization measurements. These two compounds have the same molecular weight but their terminal chains at para positions are interchanged. Influence of molecular structure on the phase diagram and dielectric behaviour is presented. Two relaxation process revealed in the antiferroelectric phase are interpreted as collective modes: anti-phase and in-phase fluctuation of phase and amplitude. The reorientation around the short molecular axis does not contribute to the dielectric spectra.
TL;DR: In this article, several diarylethene derivatives having various substituents at the reactive carbons were prepared and the quantum yields were measured and it was shown that the cyclization and cycloreversion quantum yields varied depending on the substituent substitutions.
Abstract: Several diarylethene derivatives having various substituents at the reactive carbons were prepared and the quantum yields were measured Although the cyclization quantum yields were scarcely affected by the introduction of substituents, the cycloreversion quantum yields varied depending on the substituents