Singlet molecular oxygen photosensitized by Rhodamine dyes: correlation with photophysical properties of the sensitizers

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 1999-09, Vol.126 (1), p.51-58
• Main Authors: Stracke, F, Heupel, Ma, Thiel, E
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Exited state quenching; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Intersystem crossing; Molecular properties and interactions with photons; Phosphorescence; Physics; Radiationless transitions, quenching; Rhodamine; Singlet molecular oxygen
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/S1010-6030(99)00123-9

By measuring its IR phosphorescence the formation of singlet molecular oxygen 1O 2 photosensitized by rhodamine dyes is directly proved. The 1O 2 formation rate is compared with that expected from the low probability (≈1%) of intersystem crossing of the photosensitizers. The quantum yield for triplet population and the triplet lifetime of the investigated dyes is measured by using a laser-scanning-microscopy technique. The influence of quenching agents (nitrobenzene and COT) is discussed. It results that the formation of 1O 2 can be prevented effectively by quenching of the S 1 or T state of the photosensitizer. The influence of the molecular ground-state oxygen 3O 2 concentration [ 3O 2] is investigated. The presence of the paramagnetic 3O 2 leads to an increased S 1→T intersystem crossing rate of the photosensitizers and therefore to a reinforced formation of singlet molecular oxygen. It is found for rhodamine 6G as well as for rose bengal that in air-saturated acetonitrile nearly the half of the excited dye triplets are quenched by molecular oxygen. The 1O 2 concentration can be significantly reduced by decreasing the 3O 2 concentration below its air saturated level.