Acid–base properties of disodium 3,3′-disulfonatobenzophenone (DSB) in the ground and excited states

Abstract

The photophysical parameters of the DSB–DSBH⁺ system have been determined using absorption and emission stationary and pulsed techniques. Only the neutral form was found to emit room-temperature phosphorescence with a quantum yield of 6 × 10^–2 and a lifetime on the microsecond scale. These parameters were found to decrease with increasing DSB concentration and decreasing pH, owing to self-quenching (k_sq= 8.4 × 10⁶ dm³ mol^–1 s^–1) and interaction with the proton. The triplet state pK*(–0.7), determined from T₁→ S_o phosphorescence titration and T₁→ T_n absorption titration, indicated a marked increase in basicity of DSB upon excitation (ground-state pK=–6.6).