Chinese Chemical Letters
Original article
Effects of molecular configuration of a chiral trimeric phenylene vinylene on its
liquid crystalline properties
*
Ping Yu, Zhen-Lin Zhang, Lei Wang, Chun-Luan Liu, Shi-Min Liu, Hai-Quan Zhang
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China
A R T I C L E I N F O
A B S T R A C T
Based on an analysis of the 1H NMR, FT-IR, UV–vis spectra, a chiral trimeric phenylene vinylene
derivative (ChTPV) synthesized by a Wittig reaction was determined to have a trans–cis configuration,
and it could be isomerized to the trans–trans isomer when treated with iodine. The melting point of
ChTPV with a trans–trans configuration increased by 162.1 8C compared to the trans–cis isomer, and the
ChTPV with trans–trans configuration exhibited the typical liquid-crystalline texture of the smectic A in
the heating process. The results indicated that the molecular configuration can influence the formation
of the liquid crystalline phase of ChTPV.
Article history:
Received 19 December 2012
Received in revised form 27 January 2013
Accepted 31 January 2013
Available online 14 March 2013
Keywords:
Oligomer phenylene vinylene
Configuration
ß 2013 Hai-Quan Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights
reserved.
Liquid crystalline
1. Introduction
effects on liquid crystalline properties, we report the configu-
rational character and the liquid crystalline properties of ChTPV
Oligo(phenylenevinylene)s (OPVs) have received consider-
able attention since they can be used to prepare photoelectronic
devices [1–3]. The molecular order plays a critical role in
photoelectronic device performance, for example, both charge
mobility and luminescent efficiency are influenced by molecular
aggregation [4,5]. One approach to control the molecular order
has been used to design molecules that exhibit thermotropic or
lyotropic liquid crystalline (LC) behaviors [6,7]. In addition, new
liquid crystals also can have potential applications in the fields
other than the photoelectronic devices (separation membrane
and heat-resistant materials) [8,9]. ChTPV is a chiral OPVs
derivative, which is functionalized on both ends with a R-(+)-2-
methylbutyric acid ester group. Synthesis of ChTPV and its self-
assembly properties in H2O/THF were studied in our previous
work [10,11]. The reaction sequence to prepare ChTPV is
illustrated in Scheme 1. However, the ChTPV with a trans–cis
configuration was found unexpectedly as the major isomer
based on a detailed analysis for 1H NMR and FT-IR. The cis-
configuration disturbs the formation of the liquid crystalline
phase because cis-configuration generally leads to more non-
planarity and exists in a twisted molecular conformation [12].
Furthermore, the cis-isomer isomerizes to the trans-isomer
under refluxing in toluene with iodine as a catalyst [13]. In order
to obtain the information of the molecular configuration and its
in this paper.
2. Experimental
The synthesis of the trans–cis ChTPV and trans–trans ChTPV is
outlined in Scheme 1. The detailed procedure of the trans–cis
ChTPV has been reported elsewhere [10]. The trans–trans ChTPV
was purified by column chromatography, using silica gel and
chloroform/petroleum ether (10:1) as the eluents.
Reagents were purchased from commercial sources (Aldrich)
and used without further purification. N,N-dimethyl formamide
(DMF), tetrahydrofuran (THF), carbon tetrachloride and toluene
were distilled and purged with argon before use. 1H NMR spectra
were measured in CDC13 solution at 25 8C on an AVANCZ 500
spectrometer with tetramethylsilane (TMS) as the internal
standard. FT-IR, UV–vis, and fluorescence spectra were measured,
respectively, on an E55-FRA106 FT-IR, UV-3100, and RF-5301PC
spectrophotometers. The differential scanning calorimetry (DSC,
STA449C) analysis was used with a heating and cooling rate of
10 8C/min under a dry nitrogen purge. The optical textures were
observed by polarized optical microscopy (POM, Olympus BX51)
equipped with a hot stage calibrated to an accuracy of Æ0.1 8C
(Linkam THMS600).
3. Results and discussion
The aromatic area of the 1H NMR of the two ChTPV isomers are
shown in Fig. 1. The 1H NMR spectrum of the ChTPV shows that the
* Corresponding author.
1001-8417/$ – see front matter ß 2013 Hai-Quan Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.