A STRUCTURAL INVESTIGATION OF OCTA-NORMAL-UNDECOXYPHTHALOCYANINE IN THE SOLID AND LIQUID-CRYSTALLINE STATE AND OF POLY(OCTA-NORMAL-UNDECOXYPHTHALOCYANINATO)SILOXANE BY HIGH-RESOLUTION SOLID-STATE NMR-SPECTROSCOPY

13C high-resolution NMR spectra of octa-n-undecoxyphthalocyanine (Pc) were measured in the solid and in the liquid-crystalline state. In the solid state, crystallographic splittings are observed which can be attributed to distortions of the molecular symmetry of the Pc core. These distortions are probably connected with the tilting angle between the planes of the Pc molecules and the axis of the columns formed by these molecules. Temperature-dependent measurements show that the N-H tautomerism in the Pc core displays no obvious asymmetries. Above 380 K the solid phase of the Pc molecules is transformed into a hexagonal-ordered columnar mesophase. In this mesophase the molecular Pc plane is perpendicular to the stacking axis, with the molecules rotating about the stacking axis. There is no clear deviation from the molecular D4h symmetry in the mesophase. The side chains display a liquid-like conformation in the mesophase. Poly(octa-n-undecoxyphthalocyaninato)siloxane was studied as a model of the mesophase in which the columns are chemically fixed. Solid-state NMR reveals for this polymer a rigid hexagonally ordered structure even at ambient temperature. The side chains in the polymer show the same liquid-like conformation as in the mesophase. The differences between the chemical shifts observed in solution and in the mesophase and between the solution and the siloxane polymer are attributed to intermolecular ring current shicldings and can be calculated satisfactorily by using a classical Johnson-Bovey current loop approach. © 1990, American Chemical Society. All rights reserved.