Substitution of 1,3,6,8-tetraethynylpyrene with sterically bulky trimethylsilyl groups enabled four modes of molecular packing, two polymorphs (triclinic system (Y-form) and "loose" crystal Col ho (O K -form)), a "rigid" liquid crystalline phase Col ho (O C -form), and an amorphous phase (O A -form), which emitted fluorescence at different wavelengths under UV light. The four phases could be interconverted by physical stimuli such as heating, grinding by mortar and pestle, and exposing to the vapor of organic solvents.

A series of phthalocyanine-based derivatives (m-CnOPhO)8PcCu (n= 1–20:2a–o) show two different types of mesomorphism: a flying-seed-like type forn= 1–5, a conventional molten alkyl chain type forn= 10–20, and both types forn= 6–9 in between.

DielsAlder reaction of cyclic biphenylyleneacetylene compound 3 with tetraphenylcyclopentadienone (5) realized the preparation of large-sized cyclic polyphenylene array 4. This is the first example of a cyclic polyphenylene array with a complete ring arrangement of a chiral-type CNT segment with (12,3)-structure. Transformation of 4 to the chiral-type CNT segment was attempted, but resulted in the formation of a complicated mixture probably due to the partial dehydrogenation and/or the partial elimination about the long alkyl chains. Rather efficient blue emission of the cyclic compounds 3 and 4 was discussed utilizing fluorescence quantum efficiencies and lifetimes both in their solid state and in their solution. By thermal analyses triple-melting behavior of 3 was clarified.

We have synthesized a novel series of four flying-seed-like liquid crystals (1Ph-PhO)4PcM [5-M: M = Co (5-Co), Ni (5-Ni), Cu (5-Cu) and Zn (5-Zn)] which are based on a phthalocyanine core having peripheral bulky groups without long alkyl chains, in order to clarify the precise mechanism inducing their mesomorphism. For comparison, we have also synthesized a long alkyl-chain-substituted liquid crystal ([Formula: see text]C[Formula: see text]OPhO)8PcCu (7o) having the same phthalocyanine core with long alkyl chains in the periphery. Each of the derivatives 5-M and 7o showed a hexagonal ordered columnar (Colho) mesophase. Very interestingly, the halo positions in the X-ray diffraction patterns for the Colho mesophases of the flying-seed-like liquid crystals 5-M and the long alkyl-chain-substituted liquid crystal 7o were quite differently given at 5.7–6.2 Å and 4.6–4.7 Å, respectively. The halo positions of the representative derivatives 5-Cu and 7o having the same copper phthalocyanine (PcCu) core were finely measured at various temperatures by using the temperature-variable small angle X-ray diffraction technique. As the result, the derivatives 5-Cu and 7o showed sudden jumps of halo position from 5.5 to 5.7 Å and from 4.2 to 4.6 Å, respectively, at the phase transition from the crystalline phase to the liquid crystalline phase (Colho). This means that the volume changes ([Formula: see text]V) corresponding to these halo jumps originate from two different kinds of mechanisms by sudden free rotation of the bulky substituents and by sudden melting of the long alkyl chains. Thus, in this work we have unambiguously clarified these two different mechanisms inducing mesomorphism.