The quenching rate constants of singlet oxygen by C60, H2@C60, D2@C6o, H2, and D2 in solution were measured. The presence of a hydrogen (H2@C60) or deuterium (D2@C60) molecule inside the fullerene did not produce any observable effect based on triplet lifetime or EPR measurements. However, a remarkable effect was found for the 1O2 quenching by C60, H2@C60, D2@C6o, H2, and D2. Singlet oxygen was...