Cyano-substituted stilbenes

B. Jiang, S.-W. Yang, R. Niver, and W.E. Jones, Jr., Metalloporphyrin polymers bridged with conjugated cyano-substituted stilbene units, Synth. Met., 94 205-210, 1998. 

In parallel to this example, Lewis and coworkers have also observed inverse reactivity for electron transfer and cycloaddition efficiency in the interaction of trans-stilbene with unsaturated esters (52). This result is understandable if the exciplex, rather than the radical ion pair, arranges the olefins in the correct geometry for cycloaddition. Analogous results have also been reported in the (2+2) cross photoreaction of cyano-substituted stilbenes with dienes, where all possible regioisomers were formed, eq. 16 (53a) ... 

Here, k( and k0 are the rate constants of the fluorescent and nonactivated radiationless relaxation steps, respectively. Using Eq. (8) Saltiel and D Agostino [9] determined an activation energy of approximately 13kJmol and an zlf-factor of the order of 10 2-1013s for stilbene in nonpolar solvents. Similar results have been reported for halogen- and cyano-substituted stilbenes (Table 12a). As examples, plots of log d>f versus 1/T are shown in Figure 12 for stilbene, 4-chloro-, and 4-bromostilbene. 

Lapouyade R, Czeschka K, Majenz W, Rettig W, Gilabert E, Rulliere C (1992) Photophysics of donor-acceptor substituted stilbenes. A time-resolved fluorescence study using selectively bridged dimethylamino cyano model compounds. J Phys Chem 96(24) 9643-9650... 

The preparation of cyano-substituted styryl and stilbenyl compounds can be achieved38,39 by using sodium methoxide at room temperature. In this way, o-tolunitrile has been reacted with the anil of 2-(/>-formyl-phenyl)benzo[6]furan and / -chloroaniline (52) to give 2-(2-cyano-stilben-4 -yl)benzo[6]furan (53). 

The sensitization properties of porphyrin compounds have also been improved by introducing dendron groups to the cyano substituted meso-stilbene moieties (46, 47). The aggregation of porphyrin was efficiently suppressed by the bulky dendrons while the electron injection to the conduction band of TiC>2 was improved by the cyano groups. The overall energy transfer efficiency was promoted remarkably to 2.76% for a solid DSSC. This is an encouraging result for a porphyrin dye and it offers the potential for porphyrins as alternatives to ruthenium-based dyes in the DSSC [82]. 

The effect of the cyano substitution in the bis-stilbene molecules (11) has been assessed. Intramolecular addition is the result of irradiation of dilute solutions of 4,4 - l,n-alkanediylbis[( )-2-(4-oxyphenyl)ethenyl] bispyridine. The outcome is dependent on the alkyl chain length. Cyclization is also influenced by the presence of zinc ions, since these can chelate with the pyridine nitrogen atoms. ... 

Such reactions have also been carried out on benzofurans carrying benzyl, fluoro, chloro, bromo, methoxy, cyano, and phenyl groups in the benzo ring. Substitution in the stilbene part of the molecule can also be obtained by the use of Schiff s bases derived from differing benzal-dehydes.26,28,29... 

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

---