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 SP-HPC was characterized by 1H-NMR

FTIR.SP-HPC with different degree of substitution (DSSP) of SP group was obtained.Meanwhile

DSSP of 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 DSSP of SP-HPC

bigger was the size of the micelles.The average hydrodynamic radius (Rh) of SP-HPC micelles was 140 nm when DSSP was 0.3

and this radius was increased to 299 nm when DSSP increased to 1.08.The reason for this was that the enhanced hydrophobic property with higher DSSP led 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.