Intensity dependence of fluorescence lifetimes and quantum yields from doxycycline using picosecond excitation

Abstract

The excitation-intensity dependence of the fluorescence lifetimes of doxycycline in a buffered saline solution investigated with 353 nm picosecond excitation. The excitation intensity ranges was 107109 W/cm2. The fluorescence lifetimes did not change over this range. The fluorescence profile was fitted to a double exponential with about a 100 ps fast component and a 400 psslow component. The relative-fluorescence quantum-yield measurements in the excitation intensity range of 51014 photons/cm2 to 61016 photons/cm2 displayed a linear dependence on the incident intensity up to 51015 photons/cm2, and after this intensity the quantum yield decreased monotonically. These preliminary results agree with the model of excited-state absorption at high excitation intensities. This process will affect the doxycycline photosensitization of cancer cells using picosecond pulsed excitation.