Observation of a transition from non-switchable B7 mesophase to an antiferroelectric sub-phase in strongly polar bent-core compoundsElectronic supplementary information (ESI) available: data for compounds 7, 8 and 9 as well as the general synthetic procedure for the preparation of the compounds of series II. See http://www.rsc.org/suppdata/jm/b3/b309138d/