吡喃羟丙基纤维素的合成与光响应性研究

Synthesis and Photosensitivity of Spiropyran Hydroxypropylcellulose

以N,N'-二环己基碳二亚胺/4-二甲氨基吡啶(DCC/DMAP)为催化体系,在四氢呋喃溶剂中,常温下1'-(3-羧乙基)-3',3'-二甲基-6-硝基螺[吲哚啉-2,2[2H]吲哚啉苯并吡喃](SPCOOH)与羟丙基纤维素(HPC)发生酯化反应,合成了螺吡喃羟丙基纤维素SP-HPC.通过改变SPCOOH与HPC的重量比,可以制备含有不同螺吡喃(SP)取代度(DSsp)的SP-HPC.当SPCOOH/HPC为1.5时,DSsp达到最大值1.08.SP-HPC溶解在THF中,经紫外光照射后,闭环的SP逐渐开环转变为部花菁式(MC)大共轭结构,溶液由无色逐渐变为深紫色;当溶液又置于完全黑暗环境时,开环的MC又逐渐闭环回复到SP形式,溶液又变为无色.溶液中的SP-HPC显示了快速可逆的紫外光响应特性.由于SP基团的疏水性,使得SP-HPC在水溶液中自组装为球形胶束.SP-HPC胶束显示了光响应性,闭环形式的SP吸收紫外光转变为开环形式MC,MC的大共轭结构导致基团间发生更紧密地堆叠,促使球形胶束收缩.SP-HPC固体膜显示了可逆的紫外光响应性,但是MC转化为SP的光响应速度比由SP吸收能量转化为MC的速度慢得多.

Cellulose derivatives（SP-HPC） containing different contents of spiropyran moieties were synthesized by esterification reaction between hydroxypropyl cellulose（HPC） and 3-（3＇,3＇-dimethyl-6-nitrospiro [chromene-2,2＇-indolin]-1＇-yl） propranoic acid（SPCOOH）,using dicyclohexylcarbodiimide/4-dimethylamiopryidine（DCC/DMAP） as catalyst in tetrahydrofuran at room temperature. The structure of SPHPC was characterized by1H-NMR,FTIR. SP-HPC with different degree of substitution（DSSP） of SP group was obtained. Meanwhile,DSSPof SP-HPC was increased and reached a maximum of 1. 08 when the mass ratio of SPCOOH/HPC was increased to 1. 5. SP-HPC was dissolved in THF and this solution showed rapid reversible UV light stimuli response. The colorless solution of SP-HPC in THF changed to modena after UV irradiation,and a peak at 570 nm in UV-Vis spectrum appeared and reached its maximum at 15 min,because loop-locked SP groups was transferred to ring-opening conjugated merocyanine（MC）. After the solution being placed in dark for the same time,it turned back to colorless due to the transfer of MC to SP. It was more interesting that SP-HPC was able to self-assemble to form stable spherical micelles in water with hydrophobic SP moiety collapsed in the micelles due to the amphiphilic property of SP-HPC,which were characterized by DLS and TEM. Larger was the DSSPof SP-HPC,bigger was the size of the micelles. The average hydrodynamic radius（ 〈Rh〉） of SP-HPC micelles was 140 nm when DSSPwas 0. 3,and this radius was increased to299 nm when DSSPincreased to 1. 08. The reason for this was that the enhanced hydrophobic property with higher DSSPled to more SP-HPC macromolecule aggregation. The micelles also showed stimuli response to UV light. Under UV irradiation,MC groups transferred from spiropyran type stacked more tightly,resulting in shrinkage of the micelles. SP-HPC films showed reversibly photochromic properties,but the transfer from MC to SP in dark was slower than that from SP to MC by up-taking energy.