Photoconductive bent-core liquid crystalline radicals with a paramagnetic polar switchable phase

A series of self-organizing bent-core derivatives 1[12,n], containing a highly pi-delocalized stable radical as the central angular structural element, is described. The planarity of the open-shell core permits efficient pi-pi stacking, which results in the formation of B2 and soft crystalline phases above 100 degrees C. Optical, XRD and dielectric analyses of 1[12,12] indicate that the ground state of the observed B2 phase is polar antiferroelectric of type SmCAPA exhibiting tristable electro-optical switching. SQUID and EPR measurements revealed strong antiferromagnetic spin-spin exchange interactions below the isotropic phase, which have been estimated at theta = -46 cm(-1) with the Curie-Weiss law. Transient photoconductivity was observed in the B2 phase with a hole carrier mobility mu(h) of 1.4 x 10(-4) cm(2) V-1 s(-1).