Synthesis and characterization of six-arm star-shaped liquid crystalline cyclotriphosphazenes

<正>The synthesis and mesomorphic properties of a new class of liquid crystalline cyclotriphosphazenes with rigid cyanostilbene groups and flexible alkoxy groups are reported.The thermal behaviors of cyclotriphosphazene derivatives 5a-5d are studied by the means of differential scanning calorimetry,polarizing optical microscopy.Nematic phases were observed in compounds 5a-5d both on heating and cooling.The clear temperatures of compounds 5a-5d slightly increased with increasing length of terminal alkyl chain.Compounds 5a-5d showed different mesogenic region from minimum 5℃to maximum 142℃.     

Synthesis of Cyclotriphosphazenes Containing Cyanostilbenes with Different Terminal Substituents

Abstract

The synthesis and mesomorphic properties of a class of cyclotriphosphazenes containing cyanostilbene groups with different terminal substituents (-H, -CH₃, -OCH₃, -CN) are described. All the resulting compounds are characterized by ¹ Barberá , J. ; Bardají , M. ; Jiménez , J. ; Laguna , A. ; Martínez , M. P. ; Oriol , L. ; Serrano , J. L. ; Zaragozano , I. Columnar mesomorphic organizations in cyclotriphosphazenes . J. Am. Chem. Soc. 2005 , 127 , 8994 – 9002 .[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]H, ¹³ An , B.-K. ; Lee , D.-S. ; Lee , J.-S. ; Park , Y.-S. ; Song , H.-S. ; Park , S.-Y. Stongly fluorescent organogel system comprising fibrillar self-assembly of a trifluoromethyl-based cyanostilbene derivative . J. Am. Chem. Soc. 2004 , 126 , 10232 – 10233 .[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]C, and ³¹P NMR, matrix-assisted laser desorption/ionization time of flight, and elemental analysis. The thermal behaviors of cyclotriphosphazene derivatives are studied by the means of differential scanning calorimetry and polarizing optical microscopy. Nematic phases are observed in cyclotriphosphazenes with terminal substituents (-CH₃, -OCH₃, -CN).     

通过增强电荷转移激发态构建激发态下稳定的基于氰基二苯乙烯的E/Z构型

The E/Z isomerization reaction is found extensively in most organic molecules containing double bond unit. This limits their practical application as luminescent materials partly, especially under photoirradiation. Therefore, it is important to obtain E/Z isomers with stable configuration in the excited state after photoirradiation. It is well known that cyanostilbene and its analogues play an important role in the development of organic opto/electronic materials. The substituted cyano group on C＝C double bonds has strong electron-withdrawing ability and large steric hindrance, which benefits the formation of donor-acceptor (D-A) structures and formation of intramolecular charge transfer. In our previous work, we reported a triphenylamine-cyanostilbene molecule (TPNCF) formed by modifying the cyanostilbene structure with triphenylamine, which maintained a stable E/Z configuration as a film and in high polar solvents. According to solvatochromism mechanisms and the results of theoretical calculations, we proposed that the charge transfer (CT) excited state between the triphenylamine donor and cyanostilbene acceptor groups induced the stable configuration of the E- and Z- isomers under photoirradiation. Under irradiation, the E/Z isomerization process occurring at a higher energy locally excited (LE) state was suppressed by a rapid internal conversion process from the LE to CT state. This work inspired us to provide a universal and effective molecular design strategy by modifying D-A substituents on double bonds that can successfully stabilize E/Z isomers. To further confirm that the CT excited state induced stable E- and Z- isomers in the cyanostilbene structure under photoirradiation, we designed and synthesized a donor-acceptor phenoxazine-cyanostilbene molecule (PZNCF) and successfully characterized its two E/Z isomers. In comparison with the reported TPNCF molecule, the in-situ NMR and UV spectra of E- and Z- isomers of PZNCF demonstrated that the E/Z isomerization rate became slower under photoirradiation, which indicated that the stronger electron-donating group of phenoxazine substituted in the cyanostilbene structure induced a more stable E/Z isomer configuration in its excited state. DFT calculations and photophysical results indicated that a stronger CT state was generated in both E- and Z- isomers of PZNCF. This further confirmed our hypothesized mechanism where the stable E/Z configuration can be obtained under photoirradiation by forming a suitable donor-acceptor structure to suppress the E/Z isomerization reaction in the LE state by a rapid internal crossing process from the LE to CT state. This molecular design strategy is of great significance to organic photochemistry and photoelectronics for molecules with double bond units.