Converting Nonliquid Crystals into Liquid Crystals by N-Methylation in the Central Linker of Triazine-Based Dendrimers

Abstract

Two triazine-based dendrimers were successfully prepared in 60-75% yields. These newly prepared dendrimers 2a and 2b containing the -NMe(CH2)2NMe- and the -NMe(CH2)4NMe- linkers between two G3 dendrons, respectively, exhibit columnar phases during the thermal process. However, the corresponding dendrimers 1a and 1b containing the -NH(CH2)2NH- and the -NH(CH2)4NH- linkers between two G3 dendrons, respectively, do not show any LC phases on thermal treatment. Computational investigations on molecular conformations reveal that N-methylation of the dendritic central linker leads dendrimers to possess more isomeric conformations and thus successfully converts non-LC dendrimers (1a and 1b) into LC dendrimers (2a and 2b).

Design of a Peripheral Building Block for H-Bonded Dendritic Frameworks and Analysis of the Void Space in the Bulk Dendrimers

“…The dendrons with tert -butyl amide groups on peripheral benzene were prepared according to our previous procedure (Figure S1) 71–76 . Dendrimers ( t - Bu - G 2 N ) 2 , CC ( t - Bu - G 1 N ) 3 and ( t - Bu - G 1 N ) 2 were synthesized as summarized in Fig.…”

Unconventional Approaches to Prepare Triazine-Based Liquid Crystal Dendrimers

“…However, this should convert several of the dendronic halves at the anti -position of C 4 H 8 linker to the syn -position. Specifically, dendrimer 13 should have three isomers in the solid state, as shown in Figure 7 [ 64 ], although most of the 13 exists as the form of isomer 13-I and, as expected, dendrimer 13 exhibited a columnar phase on thermal treatment ( Figure 8 ). The mesogenic range is from ~111 to ~123 °C on heating and from ~115 to ~94 °C on cooling.…”

“…Although methylation of nitrogens in the central linker of dendrimers converts non-mesogenic 10 and 12 to become mesogenic 13 and 14 , respectively, the isomeric effect seems to not be significant in reducing intermolecular face-to-face π–π interactions, allowing dendrimers 13 and 14 to be looser in the solid stacking than dendrimers 10 and 12 . Based on the optimal conformation of 13 [ 64 ], it was discovered that four intramolecular H-bond interactions arise between N a (a = 7, 8, 9, 10) and H (at C b ; b = 1, 4, 5, 6), respectively, as shown in Figure 9 . Accordingly, only two intramolecular H-bond interactions arise between N a (a = 5, 6) and H (at C b ; b = 1, 4,) in dendrimer 10 .…”

“…Intermolecular H-bond interactions can also be applied to prepare 1,3,5-triamino- s -triazine-based dendrimers with the columnar phase. Figure 13 shows an example of a central core with a C 2 symmetry that can be efficiently prepared according to the literatures [ 62 , 63 , 64 , 65 , 66 , 67 ]. Incorporating special functional groups at the periphery of dendrons can give desired physical properties to the LC triazine-based dendritic mixtures.…”

“…Based on the optimal conformation of 13 [64], it was discovered that four intramolecular H-bond interactions arise between Na (a = 7, 8, 9, 10) and H (at Cb ; b = 1, 4, 5, 6), respectively, as shown in Figure 9. Accordingly, only two intramolecular H-bond interactions arise between Na (a = 5, 6) and H (at Cb; b = 1, 4,) in dendrimer 10.…”