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Three series of dibenzo[a,c]phenazines were prepared in an order to assess the impact of side chain position on the phase stability of columnar liquid crystals. Each series was composed of four isomeric compounds differing only in the disposition of hexyloxy and decyloxy chains around the central aromatic core, giving rise to electronically similar compounds with varying shapes and symmetries. The substitution pattern was found to have a moderate effect on the clearing transition of the liquid crystal but a larger impact on the melting temperatures. These observations suggest a viable strategy for controlling the phase range of liquid crystals via judicious choice of peripheral chain structure and location. Key words: liquid crystals, self-assembly, symmetry, organic synthesis. Nous avons prepare trois series de dibenzo[a,c]phenazines en vue d'evaluer les effets de la position de la chaine laterale sur la stabilite de phase de cristaux liquides colonnaires. Chaque serie comptait quatre composes isomeriques qui se distinguaient uniquement par la disposition des chaines hexyloxy et decyloxy autour du noyau aromatique central, ce qui donnait lieu a des composes similaires sur le plan electronique et dont la forme et la symetrie variaient. Nous avons observe que l'arrangement des substituants avait un effet modere sur la transition nematique-isotrope du cristal liquide, mais un effet plus important sur les temperatures de fusion. Ces observations permettent d'envisager une strategie pratique permettant de moduler l'intervalle de transition de phase des cristaux liquides par un choix judicieux de la structure et de la position des chaines peripheriques. [Traduit par la Redaction] Mots-cles : cristaux liquides, autoassemblage, symetrie, synthese organique., Introduction The unique ability of liquid crystals (LCs) to simultaneously exhibit both order and fluidity has been exploited in an enormous variety of applications, including display devices, (1,2) holography, (3) [...]