Viologen-based photochromic materials with photochromic and photoluminescent abilities have great advantages in anti-counterfeiting. Two novel viologen-based multifunctional Ln-MOFs Eu2Cl(m-bpybdc)L2(NO3)2‧(H2O)5 (1) and Tb2Cl(m-bpybdc)L2(NO3)2‧(H2O)6 (2) (m-bpybdc=1,1′-bis(3-carboxyphenyl)-4,4′-bipyridinium, H2L = isophthalic acid) with a...