Supramolecular Structure, Physical Properties, and Langmuir-Blodgett Film Formation of an Optically Active Liquid-Crystalline Phthalocyanine

The structure and physical properties of optically active, metal‐free 2,3,9,10,16,17,23,24‐octa (S‐3,7‐dimethyloctoxy)phthalocyanine ((S)‐Pc(8,2)) are reported and compared with those of the phthalocyanine with (R,S) side chains (mixture of 43 stereoisomers). Unlike the latter compound, (S)‐Pc(8,2) lacks a crystalline phase. A freshly prepared sample is in a distorted mesophase and reorganizes irreversibly to a more ordered phase above 65 °C. X‐ray diffraction and circular dichroism studies indicate that the molecules are stacked in columns which have a hexagonal arrangement and a left‐handed helical superstructure, that is, a novel chiral Dh* mesophase. Solid state NMR measurements reveal that the phthalocyanine units in the columns begin to vibrate laterally when the temperature is increased. At 111 °C (Dh* → Dr transition) they start to rotate around their columnar axes and at the same time the side chains become liquidlike. Energy migration is very efficient in the chiral Dh* phase and also in the frozen mesophase below 3 °C, as follows from luminescence spectroscopy. Intracolumnar charge transport, studied by the time‐resolved microwave conductivity technique, turns out to be slower in the helically distorted columns than in linear columns. (S)‐Pc(8,2) forms a very stable bilayer at the air‐water interface, which can be transferred to give a high quality Langmuir‐Blodgett film. The fact that this phthalocyanine is mesogenic at room temperature is thought to be responsible for this behavior. A novel chiral Dh* mesophase is observed for the optically active phthalocyanine (S)‐Pc(8,2) at room temperature. The compound remains liquid crystalline over a wide temperature range. Intracolumnar energy migration and charge transport are studied. (S)‐Pc(8,2) forms stable multilayers at the air‐water interface, which can be deposited onto a substrate.