Efficiency of singlet oxygen generation of aminosquarylium cyanines

Several symmetrical N-methylamino- and N,N-diethylaminosquarylium cyanine dyes bearing benzothiazole, benzoselenazole and quinoline nuclei, displaying strong absorption within the “phototherapeutic window” (600–1000 nm), were investigated for the efficiency of singlet oxygen production, aiming their potential sensitising ability for photodynamic therapy (PDT). The assessment was performed determining the corresponding quantum yields of singlet oxygen generation, measuring the luminescence decay of the dyes in the near infrared. By combining the exhibited absorption and the obtained quantum yields, some of the dyes can be regarded as potential candidates as sensitizers for PDT.