Block functional chromophore

The lignin model compounds selected for this study possess two functional groups, a phenolic hydroxyl group, and an aliphatic hydroxyl group located on the side chain para to the phenolic hydroxyl group. Experiments were performed to determine the effect of blocking each of these two sites relative to the formation of chromophoric structures. 

Chromophore Functionalization of DNA Bases via Synthesis of DNA Building Blocks... 

Fig. 4 General synthetic strategy to obtain block copolymers with azobenzene-containing side-groups via polymeranalogous reaction (open circles) protected functional groups, (filled circles) functional groups, (rectangles) azobenzene chromophore units...

Subsequently the polybutadiene segment was functionalized by quantitatively converting the olefin double bonds of the 1,2-polybutadiene block via a hydroboration reaction to hydroxyl functions. In the last step various azobenzene-chromophores were attached via a polymeranalogous reaction. The synthesis and characterization as well as photophysical aspects of block copolymers based on an amorphous polystyrene block and a functionalized 1,2-polybutadiene block... 

Elimination of the 12a-OH function would extend the chromophore (by producing an additional DB at 12a-l) and eliminate activity. Substituting a halogen into position 11a would constitute a chromophoric block. Both of the preceding actions would predictably result in considerably decreased activity. 

Optical densities at 269.5 nm for polystyrene solutions at concentrations of 0-1 X 10"2 mole/liter and for poly(styrene-co-methyl methacrylate) solutions at a total concentration of 1 X 10 2 mole/liter are presented in Figure 1 as functions of styrene content. The solvents were (from the top) dioxane, chloroform, tetrahydrofuran (THF), tetrachloroethane (TCE), and dichloro-ethane (DCE). It is evident that the linear relationship between optical density and styrene concentration that is valid for a polystyrene at all concentrations (open circles) does not hold for the statistical copolymers (solid circles). For example, copolymer (25-80 mole % styrene) solutions in chloroform deviate markedly from linearity the maximum per cent decrease in extinction coefficient (hypochromism) corresponds to a copolymer containing 50 mole % styrene. We define hypochromism as the decrease in absorption intensity at 269.5 nm per chromophore of the statistical copolymer relative to that of the atactic polystyrene. It is also evident from Figure 1 that the alternating copolymer also gives a sharp hypochromism whereas block copolymers and mechanical mixtures of polystyrene and poly (methyl methacrylate) do not deviate from the straight line. Similar results were obtained with the other solvents, but the composition range where hypochromism appears depends on the solvent used. 

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