Photoinduced alkaline pH-jump on the nanosecond time scale

The triphenylmethane leucohydroxide salt 4-(dimethylamino)-4 '-(trimethylam monium) triphenylmethanol iodide has been used as a photoactivatable caged hydroxide to rapidly increase the pH of a neutral aqueous solution on the n anosecond time scale. Photoexcitation of the compound with a nanosecond ult raviolet laser pulse results in the formation of a colored carbocation with a rate greater than 10(8) s(-1); recombination occurs with a multiexponent ial kinetics. The dissociation is completely reversible on time scales of 1 0(2) s and offers a large time window after the pH-jump, in which the proto n transfer reactions can be studied. The effectiveness of the photodissocia tion process to increase the pH of the solution has been demonstrated by me ans of the pH indicator bromoxylenol blue. (C) 2001 Elsevier Science B.V. A ll rights reserved.