Photostability of pyrromethene 567 laser dye solutions via photoluminescence measurements

The effects of antioxidant addition and concentration on the photostability of methanol solutions of the pyrromethene laser dye 1,3,5,7,8 -pentamethyl-2,6-dimethylpyrromethene-difluoroborate complex (PM-567) were investigated. Specifically, methanol solutions of PM-567 were irradiated with 532 nm Nd:YAG laser pulses (2nd harmonic), and the photoluminescence measured as a function of accumulated laser pulses. The decrease in the photoluminescence-to-initial photoluminescence ratio with accumulated laser pulses was measured as a function of antioxidant addition and dye concentration. The addition of antioxidants, 1,4-diazabicyclo[2.2.2] octane (DABCO) and sodium azide (NaN3), resulted in a dramatic enhancement of photostability. whereas only nominal enhancement was observed upon n-propyl gallate addition. Over the concentration range 6 x 10(5) to 5 x 10(4) M, dye-photostability was virtually concentration independent, with only a small enhancement at lower concentrations. The normalized photostability, the half-life of accumulated energy per mole of dye, could not explain the concentration dependence of photostability. Reasons why the normalized photostability fails to explain the concentration trends are discussed. (C) 2001Elsevier Science Ltd. All rights reserved.