New liquid crystalline materials based on two generations of dendronised cyclophosphazenes

Abstract

[EN]: A divergent approach was used for the synthesis of dendritic structures based on a cyclotriphosphazene core with 12 or 24 hydroxyl groups, by starting from [N3P3(OC6H4OH-4)6] and using an acetal-protected 2,2-di(hydroxymethyl)propionic anhydride as the acylating agent. Hydroxyl groups in these first- and second-generation dendrimers, G1-(OH)12 or G2-(OH)24, were then condensed in turn with mono- or polycatenar pro-mesogenic acids to study their ability to promote self-assembly into liquid crystalline structures. Reactions were monitored by using 31P{1H} and 1H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by using different spectroscopic techniques and mass spectrometry (MALDI-TOF MS). The results were in accordance with monodisperse, fully functionalised cyclotriphosphazene dendrimers. Thermal and liquid crystalline properties were studied by using optical microscopy, differential scanning calorimetry and X-ray diffraction. The dendrimer with 12 4-pentylbiphenyl mesogenic units gives rise to columnar rectangular organisation, whereas the one with 24 pentylbiphenyl units does not exhibit mesomorphic behaviour. In the case of materials that contain polycatenar pro-mesogenic units with two aromatic rings (A4 vs. A5), the incorporation of a short flexible spacer connected to the periphery of the dendron (acid A5) was needed to achieve mesomorphic organisation. In this case, both dendrimer generations G1 A5 and G2 A5 exhibit a hexagonal columnar mesophase. [ES]: En este trabajo se ha usado un método divergente para obtener estructuras dendríticas no convencionales basadas en un núcleo de ciclotrifosfazeno con doce o veinticuatro grupos hidroxilo, partiendo de [N 3P3(OC6H4OH-4)6] y utilizando como agente acilante un anhídrido protegido derivado del ácido 2,2-bis(hidroximetil)propiõnico. Los grupos hidroxilo en estos dendrímeros de primera y de segunda generaciõn, G1-(OH) 12 or G2-(OH)24, se condensaron con ácidos promesõgenos mono o policatenares para estudiar su capacidad para promover estructuras cristal líquido. Las reacciones se monitorizaron por espectroscopia de RMN de 31P{1H} y 1H, y la estructura química de los materiales resultantes se confirmõ mediante diferentes técnicas espectroscõpicas y espectrometría de masas (MALDI-TOF). Los resultados están de acuerdo con ciclofosfazenos monodispersos y completamente funcionalizados. Las propiedades térmicas y mesomorfas se estudiaron por microscopía õptica, calorimetría diferencial de barrido y difracciõn de rayos-X. El dendrímero que tiene 12 unidades mesõgenas 4-pentilbifenilo da lugar a organizaciones columnares, mientras que aquel con 24 unidades de este tipo es un material isõtropo. En el caso de las unidades promesõgenas policatenares con dos anillos aromáticos se necesitõ incorporar un corto espaciador flexible en la periferia del dendrõn para conseguir organizaciones mesomorfas en ambos dendrímeros, de primera y segunda generaciõn. En este caso, ambos dendrímeros exhiben una mesofase columnar hexagonal. The generation game: A divergent approach was used for the synthesis of first- and second-generation dendritic structures based on a cyclotriphosphazene core (see figure). These structures were functionalised with mono- or polycatenar pro-mesogenic units. The liquid crystalline properties of the resulting materials were studied. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by the MICINN, Spain, under the projects MAT2011-27978-C02-01, CTQ2009-09030 and CTQ2011-22589, FEDER funding, Fondo Social Europeo, and Gobierno de Aragón (Dpto. de Ciencia, Tecnología y Universidad).Peer Reviewe