Published: May 02, 2011 r2011 American Chemical Society 7872 dx.doi.org/10.1021/ja200822z | J. Am. Chem. Soc. 2011, 133, 7872–7881 ARTICLE pubs.acs.org/JACS Influence of Flexible Spacers on Liquid-Crystalline Self-Assembly of T-Shaped Bolaamphiphiles Xiaohong Cheng,* ,†,‡ Feng Liu, § Xiangbing Zeng, § Goran Ungar,* ,§,^ Jens Kain, || Siegmar Diele, || Marko Prehm, ‡,|| and Carsten Tschierske* ,‡ † Department of Chemistry, Key Laboratory of Medicinal Chemistry for Natural Resources (Ministry of Education), Yunnan University, Kunming, Yunnan 650091, P. R. China ‡ Organic Chemistry and ) Physical Chemistry, Institute of Chemistry, Martin-Luther University Halle-Wittenberg, D-06120 Halle, Germany § Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S13JD, U.K. ^ WCU program Chemical Convergence for Energy and Environment, School of Chemical and Biological Engineering, Seoul National University, Seoul, Korea b S Supporting Information 1. INTRODUCTION The investigation of molecular self-assembly is one of the most exciting areas of contemporary chemical research. 1 Liquid-crystal- line (LC) systems 2,3 combine order and mobility and therefore can be regarded as simple model systems in which the driving forces of self-assembly at the nanoscale level can be studied in a systematic and controlled manner. 4 LC dendrimers 5,6 and supermolecules, 7 chirality-induced LC superstructures, 8 formation of ferroelectric organic materials and spontaneous achiral symme- try breaking in mesophases formed by bent-core molecules, 9 as well as LC magnets 10 and liquid quasicrystals 11 are selected topics of contemporary research in this rapidly developing field. Based on the concept of competitive polyphilicity, it was also possible to increase the complexity of LC phases considerably. 1216 This concept was successfully applied to two types of T-shaped ternary amphiphiles incorporating a rigid rodlike core, namely bolaamphiphiles 12,13,15,17 and facial amphiphiles. 15,18 A major group of LC phases formed by these polyphilic tectons represent polygonal cylinder phases. In these soft honeycomb structures the rodlike cores organize into cylinder frameworks, held together by attractive interactions between the terminal groups located at the edges of the cylinder walls and the resulting cells are filled with the disordered lateral chains. 15 In these structures the length of the rigid core with respect to the volume of the lateral chains determines the number of rodlike cores organized in the circum- ference of the cylinders. In this way, increasing the volume of the lateral chains at constant core length leads to a series of cylinder structures starting with rhombuses, followed by pentagons, regular and stretched hexagons, 19 and ending with giant pentagons (Figure 1cg), 12,15 followed by a bursting of these cylinders 17b with formation of a new kind of lamellar phases (Lam, Figure 1hk). 20 For the series of bolaamphiphilic biphenyl derivatives with lateral alkyl (Hm-1/1) or semiperfluoroalkyl substituents Received: January 27, 2011 ABSTRACT: T-shaped bolaamphiphiles composed of a biphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the polar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Col hex /p6mm, Col rec /p2gg, Col squ /p4gm and Col squ /p4mm), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Col rec /c2mm phase made up of rhombic cylinders with the Col squ /p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col rec /p2gg to Col squ /p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds.