Synthesis of novel helical poly(N-propargylamides) containing azobenzene pendant groups and effects of substitution groups on azobenzene on the stability of helix

A series of novel N-propargylamides bearing substituted azobenzene pendant groups (R-C6H4-N=N-C6H4-CONHCH(CH3)CONHCH2C CH, R = CH3CH2N(CH2)(2)OOC(CH2)(3)CH3 (V-1), R = CH3CH2N(CH2)(2)OOCCH2NHCOCH3 (V-2), R = H (V-3)) were synthesized and polymerized with [Rh(nbd)Cl](2) as a catalyst to obtain the corresponding polymers (Poly(V1-3)). The azobenzene chromophores in the side chains of Poly(V-1,V-2) contained bulky electron-donating substituents, while the azobenzene in Poly(V-3) did not bear this kind of substituent The introduction of substituted azobenzene chromophores into the side chains of poly(N-propargylamides) was found to increase the hydrogen bond strength, steric repulsion and electrostatic interactions between the neighboring side chains. These factors worked together to improve the helical stability of poly(N-propargylamides). The solubility of these poly(N-propargylamides) was increased by introducing substituents into the azobenzene chromophores. CD and UV-vis spectra showed that all the poly(N-propargylamides) took the helical structures with predominantly one-handed screw sense, which were tight helices. Furthermore, the unsubstituted azobenzene groups in the side chains of Poly(V-3) also arranged to form the helical conformation. The helical structures of Poly(V1-3) remained stable at various temperatures (5-60 degrees C). Poly(V-1,V-2) exhibited good helicity in polar solvent, which indicated that the bulky substituents, electrostatic and steric repulsion between the adjacent side chains lessened the effect of polar solvent on the hydrogen bonding. The main chains of Poly(V-1,V-3) still kept helical sense after the isomerization of trans-azobenzene to the cis form upon UV irradiation. The helical array of azobenzene side chains in Poly(V-3) experienced reversible arrangement-disarrangement upon photoirradiation. (C) 2015 Elsevier Ltd. All rights reserved.