PHOTOCHEMICAL BEHAVIOR OF BETA-CARBOLINES .4. ACID-BASE EQUILIBRIA INTHE GROUND AND EXCITED-STATES IN ORGANIC MEDIA

The protonation equilibrium of six beta-carbolines has been studied in organic media. The pK(a) values in acetonitrile were determined by sp ectrophotometric methods. The pK(a) values in the first excited single t state (pK(a)) were calculated from the Forster cycle and the values compared with those obtained by fluorimetric titration, It is conclud ed that the acid-base equilibrium is not established during the lifeti me of the excited state, The differences between the pK(a) of the grou nd and the electronic excited singlet states in different organic medi a (MeOH, EtOH, Pr'OH, Bu'OH, MeCN and CH2Cl) were also calculated.