From Sponges to Nanotubes: A Change of Nanocrystal Morphology for Acute‐Angle Bent‐Core Molecules

Abstract

The crystalline (B4) phase made of acute‐angle bent‐core molecules (1,7‐naphthalene derivatives), which exhibits an unusual, highly porous sponge‐like morphology, is presented. However, if grown in the presence of low‐weight mesogenic molecules, the same crystal forms nanotubes with a very high aspect ratio. The nanotubes become unstable upon increasing the amount of dopant molecules, and the sponge‐like morphology reappears. The phase is optically active, and the optical activity is an order of magnitude smaller than in the B4 phase made of conventional bent‐core molecules. The optical activity is related to the spatial inhomogeneity of the layered structure and is reduced due to the low apex angle and low tilt of the molecules. The arrangement of molecules within the layers was deduced from the bathochromic absorption shift in the B4 phase.

Mesogens with central naphthalene core substituted at various positions

“…More interesting results have been reported in the series of naphthalene-1,7-diol derivatives: the crystalline B 4 phase was identified in the PIMB-derivatives with a terminal alkoxy tail [24,34,37]. Replacing the alkoxy chain for an alkylthio tail led to the sequence of hexagonal columnar Col h and B 4 phases [32,33,36,38,40]. For long alkylthio chains containing 22-30 carbon atoms also a cubic phase appeared (the sequence of Cub-Col h -B 4 was found) [36].…”

“…For long alkylthio chains containing 22-30 carbon atoms also a cubic phase appeared (the sequence of Cub-Col h -B 4 was found) [36]. Further it was observed that the B 4 phase for C16 and C20 alkylthio terminal chain derivatives exhibited highly porous sponge-like morphology [40]. Lateral substitution (F,Cl) in the outer benzene rings resulted in a decrease of transition temperatures and appearance of Col h -Cub, Col h -B 4 , Col h -Col x phase sequences.…”

“…On the other hand, joining the lengthening arms to the naphthalene-1,2-diol [23,24], naphthalene-2,3diol [23,24,[27][28][29][30] and naphthalene-1,7-diol [23,24,[31][32][33][34][35][36][37][38][39][40], and to 1,2-positions of benzene [41][42][43][44][45], results in bending angle around 60°. Such materials are referred to acute angle mesogens, U-shaped, and/or V-shaped liquid crystals, respectively.…”