One- and Two-Photon Excitation of β-Carbolines in Aqueous Solution: pH-Dependent Spectroscopy, Photochemistry, and Photophysics

beta-Carboline (beta C) alkaloids are present in a wide range of biological systems and play a variety of significant photodependent roles. In this work, a study of the aqueous solution-phase photochemistry, photophysics, and spectroscopy of three important beta Cs [norharmane (nHo), harmane (Ho), and harmine (Ha)] and two beta C derivatives [N-methylnorharmane (N-Me-nHo) and N-methylharmane (N-Me-Ho)] upon one- and two-photon excitation is presented. The results obtained depend significantly on pH, the ambient oxygen concentration, and the beta C substituent and provide unique insight into a variety of fundamental photophysical phenomena. The data reported herein should not only help to understand the roles played by beta C alkaloids in biological systems but should also help in the development of methods by which the photoinduced behavior of these important compounds can be controlled.