Cyano groups chromophores

The significant influence of R1 and R2 on color is quite surprising because these substituents are not components of the chromophore system. Ester and, especially, cyano groups in these positions cause a distinct hypsochromic shift [9],... 

C NMR spectroscopy ". It is interesting that cyano groups in the 2.6-positions (567) impart unusual properties to semibullvalenes, for instance a color in the absence of any chromophor and a reversible thermochromism, while no such influence is observed in the case of the 3,7-dicyano derivatives. 

Miller s group [415-417] at IBM reported two series of statistical PF copolymers using perylene and cyano-substituted phenylene vinylene chromophoric segments (Scheme 2.51). 

The optical properties of chromophores can be varied by means of substituents. Electron donors (e g., alkyl, alkoxy, or substituted amino groups) and electron acceptors (e g., cyano, alkylsulfonyl, or carbalkoxy groups) can intensify fluorescence depending on their position on the chromophore. 

Although the synthesis of each chromophore material is to some extent unique (and hence requires individual description which is beyond the scope of this review), most chromophores used for device prototyping involve amine donor moieties. Thus, once a large quantity of aldehyde-terminated amine do-nor/partial bridge material has been synthesized, it can be reacted via Knoeve-nagel condensation with a variety of acceptor groups to form different series of chromophores. The acceptor in Schemes 1-4 is 3-cyano-5,5-dibutyl-2-dicy-anomethylene-4-methyl-2,5-dihydrofuran (which we refer to as the cyanofuran, CF, acceptor). This is synthesized by a literature method [213]. 

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