Tolane-based bent bolaamphiphiles forming liquid crystalline hexagonal honeycombs with trigonal symmetry

Abstract

Fluorescent bent bolaamphiphiles self-assemble into non-centrosymmetric honeycombs with p3m1 symmetry, which can be solvent-stabilized to form lyotropic LC phases.

Synthesis and self-assembly behavior of 2,5-diphenylethynyl thiophene based bolaamphiphiles

“…Kumada coupling reaction between 3-bromothiophene and n-alkyl Grignard reagents yielded the 3-alkylthiophenes (2/n) [18], which were diiodinated with N-iodosuccinimide (NIS) [19]. The obtained 2,5-diiodo-3-alkylthiophenes 3/n were then coupled with 1,2-O-isopropylidene glycerol substituted phenylacetylene 4 [17,20] in a Sonogashira coupling reaction, affording the 1,2-O-isopropylidene glycerol substituted 2,5-bis(phenylethynyl)thiophene 5/n. In the last step the 1,2-O-isopropylidene groups were cleaved with pyridinium p-toluenesulfonate (PPTS) in CH 3 OH [20,21].…”

“…A comparison of compounds 1ET/n with previously reported related 2,5-diphenyl thiophene based bolaamphiphiles 1T/n [9] and 1,3-bis(phenylethynyl)benzene based bolaamphiphiles 1EP/n [17] provides additional insight. As reported, stable higher symmetry LC phases, including Col squ / p4mm, Col squ /p4gm, and Col hex /p6mm phases, are found in 2,5-diphenyl thiophene based bolaamphiphiles 1T/n.…”

“…The phase transition temperatures and associated enthalpy values of the synthesized compounds 1ET/n together with the previously reported compounds 1T/n [9] and 1EP/n [17] are summarized in Table 1. Compounds 1ET/n are all crystals without liquid crystalline properties in their pure states.…”

“…As part of our research work on functional bolaamphiphiles, herein we have further introduced both thienyl and acetylene units into the rigid core simultaneously and obtained a new series of bentshaped 2,5-diphenylethynyl thiophene based bolaamphiphiles 1ET/n and compared them with the related compounds 1T/n [9] without ethynyl units and compounds 1EP/n [17] with phenyl instead of thienyl as the central unit in the rigid core (see Scheme 1).…”

“…In order to introduce functionality into such soft nanostructures for their potential applications, oligothiophene segments [9][10][11][12][13] and ethynlene [14] units have been employed respectively as rod-like building blocks. Till now honeycomb-type columnar phases with triangular, square, and hexagonal cells have been found for functional bolaamphiphiles based on bithiophene [10b,11], tetrathiophene [10a,12] and sexithiophene [13] cores by varying the length and number of the lateral alkyl chains, and recently even the honeycomb-type columnar phase with noncentrosymmetric trigonal p3m1 symmetry (Col hex-3 /p3m1), which is of potential interest for nonlinear optics applications [15] has been found for bolaamphiphiles with p-conjugated 1,3-bis(ethynyl)benzene bent-core [16,17].…”