Photosensitizing Merocyanine Dyes Based on Selenobarbituric Acid

Structural analogs of Merocyanine 540 (MC540) were synthesized to probe biological mechanisms of action and to enhance viral inactivation. Novel pyrimidine-2- selone analogs of known and modified merocyanine sensitizers are described. A surprising result of placing selenium at the barbiturate site was the ∼ 100-fold enhancement of photogeneration efficiency for singlet oxygen (1O2). Conversely, selenium directly attached to the chromophore π-system was much less efficacious. The production of more 1O2 is reflected in greatly improved biological effectiveness of the new dyes. A puzzling high to low bioactivity isomer effect among molecules containing naphthoxazole or naphthothiazole components is shown by both thione and selone dyes.