Fluorescence Confocal Polarizing Microscopy of a Fluorescent Bent‐Core Liquid Crystal Exhibiting Polarization Splay Modulated (B7) Structures and Defects

Abstract

The B7 phases of bent-core molecules are polarization splay modulated fluid smectics that exhibit an unusually complex variety of exotic macroscopic structures, textures, and defects visible in polarized light microscopy. Herein we describe optical studies of these structures using fluorescence confocal polarizing microscopy (FCPM) and depolarized transmission optical microscopy to probe their organization in three dimensions. These experiments utilize recently reported fluorescent bent-core molecules designed to give strong polarized fluorescence. This new bent-core molecular family provides the means for probing a variety of bent-core phases and structures by using FCPM and multiphoton fluorescence nonlinear imaging techniques. Comparative textural analysis of the B7 structures obtained using different types of imaging and the corresponding structural models are discussed.

Nanoscale structures of polarisation-modulated bent-core materials in thin films

“…Such texture is similar to coiling freestanding filaments [28] suggesting that the stripes of the myelinic textures also have concentric layer structures such as of the freestanding and helical filaments, except that they are probably flattened by the bounding surfaces, as shown in the inset of Figure 2b. Indeed, recent fluorescence confocal polarising microscopy studies [29] have lead to the same conclusions.…”

Airflow-aligned helical nanofilament (B4) phase in topographic confinement

“…In the B2 smectic layers, the layer polarisation and chirality of the B2 phase can be racemic or homo-chiral; however, the bent-core molecules are definitely closely packed with uniform polar and tilt senses. In contrast, the in-plane layers of the B7 phase are spatially modulated with a specific periodicity, in which the polar and tilt directors of the molecules are continuously changed, resulting in various types of characteristic textures such as spiral textures consisting of smectic filaments and myelin-like, accordion-like, checker-board-like, banana-leaf-like, and circular domain textures 6 25 . Thus, the molecules and superstructures of HNFs of MHOBOW can be more frustrated than those of NOBOW in our experimental system.…”

B7 Liquid Crystal Filament Growth in Presence of Carbon Nanotubes

“…Also to be seen are areas with focal conic domains and leaf‐like domains. There is thus a hierarchy and variation of structures and patterns to be observed, which is common for the B7 phase and which has been studied in detail by Deb et al., with polarized optical microscopy (POM) as well as fluorescence confocal polarizing microscopy (FCPM). For reasons of illustration and clarity we have also added enlarged images of single‐ [part (b)] and double‐twisted [part (c)] filaments in orientations to the crossed polarizers of 0°, 45° and 90°, because these will be of the prime interest for this investigation.…”

“…At least seven principle bent‐core liquid crystalline phases have been discovered so far, of which the B7 phase is probably the most intriguing and most complicated at the same time. On cooling from the isotropic melt, a wealth of structural features can be identified by polarizing microscopic observation, such as the formation of left‐and right‐handed helices, and single‐ and doubly‐twisted ribbons, similar to normal and super‐twisted telephone cords, but also domains with equidistant striped patterns which indicate some twisted, or undulated structures ,…”