Biphenyl 3-cyano-4 -methoxy

The photodecarbonylation of a series of dibenzyl ketones was studied by Robbins and Eastman/63 The results of this study are presented in Table 4.5. The data in Table 4.5 indicate that the presence of a p-methyl or a p-methoxy group has little effect on the quantum yield for this reaction. p-Cyano groups, on the other hand, essentially totally eliminated the decarbonylation. Since the reaction could also be quenched (inefficiently) by benzonitrile or biphenyl, it was concluded that the decarbonylation occurs from a short-lived triplet state. The effect of the p-cyano groups then could result from internal triplet quenching. 

Ar = alkyl, methoxy, nitre, cyano, halophenyl derivatives, 2-biphenyl... 

The substitution of a methoxy group on the phenyl ring suppressed the mesophase, whereas a cyano group stabilized the SmA phase. When two long chains were grafted on both the biphenyl and phenyl cores (R = C H2n+i, R = Cm 2m+i), mesomorphism was suppressed. 

Frank elastic constants and Leslie viscosity coefficients. Haller and Litster [41, 42] investigated the temperature dependence of the normalised scattering intensity and the scattering hnewidth as a function of temperature, finding that the latter was far more temperature sensitive. Many materials have been studied using this technique MBBA [43-45], di-butylazoxybenzene and p-methoxy-p -n-butylazoxybenzene [46-48], Schiffs bases [49-51 ], and the cyanobiphe-nyls [52, 53]. Typical data for the cyano-biphenyls are shown in Fig. 6. 

---