The photodegradation of pyrromethene 567 and pyrromethene 597 by pyrromethene 546

The photo-destabilizing action of 1,3,5,7,8-pentamethylpyrromethene difluoroborate complex (PM546) on 1,3,5,7,8-pentamethyl-2,6-diethylpyrromethene difluoroborate complex (PM567) and 1,3,5,7,8-pentamethyl-2,6-di-t-butylpyrromethene difluoroborate complex (PM597) has been investigated. Acetonitrile solutions of PM567 and PM597 demonstrated accelerated photodegradation upon the addition of PM546; whereas the photodegradation rate of the corresponding n-hexane solutions remained invariant with respect to PM546 addition. The enhanced photodegradation rate is explained by electron transfer from PM567 and PM597 to PM546. A PM546 singlet oxygen (1O2, O2 (a1Δg)) quenching rate constant of 3.86 ± 0.18 (2σ) × 107 dm3 mol−1 s−1 is obtained from infrared phosphorescence measurements of O2 (a1Δg → X3Σg−).