Doses of a bacterial suspension (200 mu L, d. 1.10(7) colony forming units in 1 mL) were deposited on substrates (stainless steel, glass, plastic) and incubated on them at 36 degrees C for 24 h to produce biofilms. The biofilms were immersed in solns. of the title compound for 20 min and exposed after bathing to light beam (wavelength 735 nm, power d. 3 mW/cm(2), 20 min). The use of light-activated title compd. resulted in significant redn. of living cells populations on all tested substrates. The biggest changes were obsd. on the glass substrate.