Direct transition from a nematic phase to a polar biaxial smectic A phase in a homologous series of unsymmetrically substituted bent-core compoundsElectronic supplementary information (ESI) available: physical and spectral data obtained for the compounds of series 1j, 1k and 1l. See http://www.rsc.org/suppdata/jm/b3/b309262c/ | doi.page