Two photochromic hybrid materials assembled from naphthalene diimide as photocatalysts for the degradation of carcinogenic dye basic red 9 under visible light

•Two electron-transfer hybrid compounds based on electron-deficient naphthalene diimide and polyoxometalate were synthesized and characterized.•Complexes 1 and 2 exhibit the eye-detectable photochromic phenomenon.•Complexes 1 and 2 show good photocatalytic activity for degradation of carcinogenic dye BR9.