A viologen-based host–guest Eu-MOF with visible photochromism and strong photoluminescence.

[Display omitted] • It is an urgent demand to achieve the multifunctional optical properties of visible photochromism and strong photoluminescence on one material. • The photochromic viologen-based MOFs rarely exhibit strong photoluminescence in both initial and colored states. • We report herein a viologen-based host-guest Eu-MOF with both visible photochromism and strong photoluminescence. • The title compound exhibits visible photochromism arising from photoinduced electron transfer from electron rich host framework to electron deficient guest viologen unit. • The title compound emits strong pink luminescence in both initial and colored states with the luminescence quantum yield of about 31.6%. A viologen-based host–guest metal–organic framework with both visible photochromism and strong photoluminescence was designed and synthesized, namely (H 2 bpyb)[Eu(btec)] 2 (bpyb = 1,4-bis(4-pyridyl)benzene, H 4 btec = 1,2,4,5-pyromellitic acid), providing an effective pathway for designing multifunctional optical materials with comprehensive performance. [ABSTRACT FROM AUTHOR]