By using spectroscopic characteristics of azo chromophores in different states as a‘probe’

H-aggregation of the azo chromospheres of a polyelectrolyte poly {2-[4-(4′-ethoxyphenylazo) phenoxy] ethyl acrylate-co-acrylic acid} (PEAPE) aqueous solutions and its effect on photo-responsive behavior were studied．Compared with the azo polyelectrolytes in DMF

PEAPE in H2O showed an obvious blue-shift of the maximum absorbance due to H-aggregation of the ago chromophores formed in the solution．There also exists H-aggregation of the azo chromospheres in PEAPE solution in DMF／H2O

and the degree of H-aggregation depends on the ratio of DMF and H2O．The UV-Vis spectra of PEAPE aqueous solution change with different degrees of functionalization of the azo chromophores. With the degree of functionalization increase

the λmax of PEAPE gradually blue shifts

which suggests the degree of H-aggregation increase. H-Aggregation of the azo chromospheres results in a slower photo-isomerization rate and lower photo-isomerization efficiency of the azo polyelectrolyte PEAPE．The photo-isomerization kinetics of the PEAPE aqueous solution doesn’t obey the first order exponential decay function

which also indicates that the coexistence of H-aggregates and “isolated” azo chromospheres in the system.