Effect of Remote Polyene Bridge Methyl Substituent on Physical Properties of Dipolar Chromophores with Conformationally and Configurationally Locked Polyene Bridge

Abstract

The effect of a C-2 substituent on the success of Knoevenagel condensation of the cycloalkenone moiety, which is usually the final step in the multi-step synthesis of conformationally and configurationally locked polyene bridged Donor - π Acceptor chromophores, has been investigated. In addition, the possibility of a two-pot synthesis of polyene bridges with more than two annulated cyclohexenyl rings and the effect of a polyene bridge methyl substituent on the planarity of the chromophore have been investigated. The results of these studies show that a C-2 on the terminal cycloalkenone of the polyenone must not be substituted for successful Knoevenagel condensation in the modular synthesis of Donor-π -Acceptor dipolar chromophores. It is also demonstrated that three new rings can be annulated in a two-pot reaction sequence. A significant blue shift in λ max of prepared rigid polyene bridge chromophores indicates that a remote methyl substituent on the polyene bridge has a dramatic effect on the planarity of the chromophore. must not be substituted for successful, final step, Knoevenagel condensation to complete the synthesis of the dipolar chromophores. We also demonstrated that three new rings can be annulated in a highly abbreviated two-pot reaction sequence. Measurements of the λ max of prepared rigid polyene bridge chromophores indicate that a remote methyl substituent on the polyene bridge has a dramatic effect on the planarity of the chromophore bridge. This conclusion is based on the observed significant blue shifts in λ max . The results of the three related studies reported herein represent important contributions to the knowledge base for the synthetic optimization of the properties of chromophoric organic materials. Monomers and polymers endowed with such optimized properties are important for the development of improved fabrication components for materials science and technology. room round the mixture. insoluble and rinsed THF until washings were colorless. THF evaporated a dark cooled to -10 o C and 30 mL of 12 cooled to 0 o C was added in portions to the stirred crude product. A yellow cake formed at bottom of the reaction flask re-dissolved after it was broken up at room temperature. The aqueous acid solution was heated at 80 o C for dehydration of the alcohol to room temperature, the aqueous solution was carefully solid sodium bicarbonate until basic to litmus paper. The product precipitated out of as an ash-colored cake. The cake was broken up and suction-filtered. The resulting was rinsed with hexane to remove an oily component. The dark gray solid product weighed after additional 1.95g of product obtained from column chromatography of the ether extracts of the aqueous on silica gel using of ethyl respectively. 42.50 g (93%). Use of n-BuLi to the nucleophile the wet distillate collected in the trap was run off every time it filled up until a viscous dark mass was left in the reaction flask. The reaction mixture was then heated for 2 h as the bath temperature rose to 140 o C. 300 mL of fresh CCl 4 was added to dissolve some of the dark mass and thin layer chromatography of the solution on silica gel with 30% ethyl acetate in hexane showed that the cyclohexenone was no more present in detectable amount. The suspension was allowed to cool to room temperature. The suspension was stirred with a solution of 20 g of K 2 CO 3 in 100 mL of distilled water to remove excess thiobarbituric acid. After the suspension was filtered, the dark solid product was rinsed with 600 mL of distilled water. The filtrate consisting of both aqueous and organic layers was reserved. The solid product was vacuum-dried for 2 days at room temperature and weighed 15.30 g. The CCl 4 layer of the filtrate was separated and the aqueous layer was extracted with CCl 4 after being saturated with solid NaCl. The combined CCl 4 extracts was dried over anh. MgSO 4 . Rotary evaporation and stirring of the resulting solid with 50 mL of CCl 4 at room temperature for 12 h led to an additional 2.37 g of product for a total of 17.67 g (~ 100%). Mp : 225.8