Discotic liquid crystals of silicon phthalocyanine-based singledeckers and doubledeckers: Influence of the axial substituent groups on their mesomorphism

Three kinds of silicon phthalocyanine derivatives axially substituted by different groups were prepared and Singledecker-C[Formula: see text]PcSiCl 2 (1a), Singledecker-C[Formula: see text]PcSi 2 (OH) 4 (3a, b) and Doubledecker-(C[Formula: see text]PcSi) 2 Cl 2 (4a, b) were obtained in order to investigate their mesomorphism for [Formula: see text] = 8 (a) and 12 (b). The mesomorphism was established by using polarizing microscopic observations, differential scanning calorimetric measurements, temperature-dependent electronic absorption spectra and temperature-dependent X-ray diffraction analysis. From the results, each of the derivatives, 1a, 3a, 3b, 4a and 4b showed columnar mesophases; 1a: Col[Formula: see text](P2 1 /a), pseudo Col[Formula: see text] and Col[Formula: see text]; 3a, b: Col[Formula: see text](P2 1 /a) and Col[Formula: see text]; 4a, b: two kinds of Col[Formula: see text]. Interestingly, each of the virgin samples of singledeckers, C 8 PcSiCl 2 (1a), C 8 PcSi 2 (OH) 4 (3a) and C 8 PcSi 2 (OH) 4 (3a), were green in color but changed into blue over ca.180–190 [Formula: see text]C by polymerization. On the other hand, each of the double-deckers, (C[Formula: see text]PcSi) 2 Cl 2 derivatives (4a and 4b), decomposed over ca. 180–240[Formula: see text]C. Thus, the influence of the axial groups is so large on their mesomorphism that they exhibit unusual mesomorphic behaviors accompanied by color change.