Stilbenoid compound

Scheme 1-64 points up one additional and important aspect to the problem of ferromagnetic coupling in dication diradicals. The stilbenoid compounds of Scheme 1-64 give N+ / N+ dication diradicals upon two consecutive one-electron oxidations (anodic or by means of NOPF6). The compound containing the methoxy group in the stilbenoid fragment has a half-life of up to two months, even under ambient conditions. This... 

The interesting photophysics and photochemistry [37, 38] of stilbenoid compounds make them suitable for applications in materials science. In addition to well-established applications, such as in optical brighteners, others arise in light-emitting diodes (LED), in non-linear optics (NLO), and in optical imaging, storage, and switching techniques. 

Whilst the above results demonstrate the clear potential of stilbenoid compounds for the photochemical synthesis of large aromatic systems, the scope has not yet been exhausted. Indeed, the ready synthetic availability of the stilbene precursors, together with the tolerance to a large selection of substituents and mild reaction conditions, make this approach particularly attractive for - and complementary to - other cyclization strategies such as the Lewis acid-mediated SchoU reaction, which is compatible with only a few classes of functional groups (vide supra). 

Due to their miscellaneous photophysical and photochemical properties, stilbene compounds can be used for many applications in materials science. Data on the photochemistry of stilbenoid compounds and their role in materials science were reviewed [1-3]. In this chapter, we briefly discuss materials for lasers, nonlinear optical systems, photoconductive materials, and imaging and switching techniques. 

Frequency upconversion of 800 nm ultrashort 175 fs optical pulses by two-photon absorption in a stilbenoid compound-doped polymer (PMMA) optical fiber was reported [28]. By the intensity-dependent transmission method, the two-photon absorption cross section was deduced. The combination of a well-designed organic chromophore incorporated into a fiber geometry is appealing for the development of an upconversion blue polymer laser. Upconversion fluorescence and optical power limiting effects based on the two- and three-photon absorption process of a frans-4,4 bis(pyrrolidinyl)stilbene were investigated [29]. The molecular TPA cross section three-photon absorption (3PA) cross section g3 at 720-1000 nm were measured. The 3PA-induced optical power-limiting properties were also illustrated at 980 nm. 

The stilbenoid compound lunularic acid (9) occurs in all liverworts examined thus far and appears to fiilfrll the same growth-regulating function in these plants that abscisic acid... 

The most comprehensive studies on shape-persistent Hekates have been performed on stilbenoid star-shaped molecules. Structures and mesomorphic properties are collected in Table 1. Core building blocks with only one repeating unit per arm and one flexible chain 26a,b, 28a-d, 30a did not show any liquid crystal properties [56-58]. In the series of two chain derivatives 28e, 30b,c the formation of meso-phases depend on the core [57-59]. The electron deficient triazine and the dicyanopyridine building block induced obviously columnar mesophases. The pyridine derivative 30b showed only a crystalline phase [58]. In the series of nine chain stars 26c-g [60-62] and 28f-n [57], the compounds formed columnar phases depending on the chain length of the peripheral chains. Propyloxy chains are too short but hexyloxy and dodecyloxy chains are sufficient for the formation of liquid crystal phases by nanosegregation [60-62]. This can be rationalised by a dense... 

Structurally, dendrimers of type 5 are best compared with rigid dendrimers made up of tolan building blocks. However, neither the form of aggregation observed in stilbenoid dendrimers, nor the phase behaviour or the photochemistry of these compounds have so far been found to occur in similar form in tolan systems. 

Suzuki-type coupling protocols were also evaluated as a method to prepare some related tetrahedral stilbenoid molecules and the optimal yields were achieved when using Pd(dppf)Cl2 as the catalyst. The cruciform materials prepared using this strategy are shown in Scheme 3.3. Compounds 5a and b were obtained as a mixture of cis and trans isomers as identified by high-performance liquid chromatographic (HPLC) analysis. Nevertheless, the mixtures were readily converted into the all-trans isomers by irradiating the dissolved samples with a mercury lamp. 

A novel topological strategy has been examined for designing amorphous molecular solids suitable for optoelectronic applications. In this approach, chromophores were attached to a tetrahedral point of convergence. For instance, stilbenoid units were covalently linked to a tetraphenylmethane core by means of a palladium-catalyzed Suzuki coupling reaction [143]. The optical properties of these compounds were examined. 

In addition, stilbenes are fluorescent compounds which are easily detected by flu-orometry. For resveratrol, fluorescence detection is highly selective and even twice as sensitive as UV detection (Stecher et al. 2001). Due to this potential, methods by using HPLC coupled with absorbance and fluorescence detection were developed (Jeandet et al. 1997 Vitrac et al. 2002). Otherwise identification of stilbenes in wine by HPLC-DAD can be limited by coelution of two or more compounds. Therefore application of modern mass-spectrometry techniques is important to confirm the structure of stilbenes and to detect novel compounds in wine (Monagas et al. 2005b Buiarelli et al. 2007 Careri et al. 2004 Jean-Denis et al. 2006 Kammerer et al. 2004 Mark et al. 2005 Piissa et al. 2006 Stecher et al. 2001). Table 9C. 1 shows an overview on stilbenoid molecular ions and fragments identified in wine and grapevine by mass spectrometry. 

Fig. 10. The electronic characters of the excited state funnel (S ) and of the ground state barrier to cis-trans isomerization S ) of stilbenoid or similar compounds are opposite and complementary...

Monodisperse oligo(phenylenevinylene)s are assembled to three-dimensional scaffolds in convergent three- or fourfold Homer reactions of a silane core and stilbenoid aldehydes in moderate to good yields. The central silane is sensitive toward nucleophilic attack. Tetrahedral compounds with short side chains form stable amorphous films but trigonal-pyramidal shaped assemblies tend to recrystallize. The connection of the chromophores to a central silicon atom results in a stabilization of the excited states an intense blue-green fluorescence is emitted from solution as well as from transparent films. 

Stilbene system is widely distributed in nature where it is found in a variety of compounds that exhibit therapeutic roles in different fields, including cancer treatment. Albeit stilbene itself is not found in nature, polyhydroxylated stilbenoids (stilbenes and bibenzyls) have been isolated from several medicinal plants [1]. 

The anti-virus activity research concerning stilbenoids mainly focuses on HIV. Glepidotin D (162) was isolated from the leaves of Glycyrrhiza lepidota as the compound responsible for the anti-viral activity with an EC50 of 2.0 g/ml and an ICso of 5.0 //g/ml, which excludes the need for further study [98]. 

In some rigid planar systems snch as 34 photochemically induced proton transfer occurs in benzene as solvent, but this is followed by cyclization resulting in the formation of the acridine 35 . The cychzation is a common oxidative process in c -stilbenoid systems. The proton transfer is an essential feature in the cyclization, since it was demonstrated that the reaction fails with the methoxylated analogue. With the bis hydroxy compound 34, X = = OH, a second cyclization affords 36 albeit in lower yield (14%). 

Star-shaped compounds having a 1,3,5-triazine core and stilbenoid arms have been prepared. These compounds form nematic discotic systems <04T6881>. Discotic liquid crystalline... 

It is also important to consider any possible deleterious effects that resveratrol and its metabolites may have on plants. Production of defensive stilbenes in plants results in resource competition between parallel biosynthetic pathways. For example, one group of metabolites that may be severely impacted by this competition is the chalcones and their metabolites that play a variety of important roles in plants. These compounds share a pool of basic precursors with the stilbenoids [134,135]. Alterations in stilbenoid production could have far reaching effects on the health of the plant. The severity of this problem has been highlighted by Fischer and colleagues [136] who reported that overexpression of a stilbene synthase gene in transgenic tobacco and petunia plants resulted male in sterility. 

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