Three isomers of N,N′-dibenzy-biquinolinium dibromide were synthesized and their photoinduced coloration properties were investigated in the thin poly(N-vinylpyrrolidone) films. Upon photo-irradiation, the colorless film of 4,4′-biquinolinium salt became intense purple and had a near IR-absorption at 970 nm, whose color gradually bleached, reaching original ones. While photo-induced absorption maxima of 6,6′-biquinolinium salt does not shift to longer wavelength and 5,5′-one exhibits thermochromism.