Abstract
Controlling the activity of biomolecules with light-triggered photocages is an important research tool in the life sciences. We describe here a coumarin photocage that unusually combines the biocompatible optical properties of strong absorption at a long wavelength close to 500 nm and high photolysis quantum yields. The favourable properties are achieved by synthetically installing on the photocage scaffold a diethyl amino styryl moiety and a thionoester group rather than the lactone typical for coumarins. The photocage's photophysics are analysed with microsecond transient absorption spectroscopy to reveal the nature of the excited state in the photolysis pathway. The excited state is found to be strongly dependent on solvent polarity with a triplet state formed in DMSO and a charge-separated state in water that is likely due to aggregation. A long triplet lifetime is also correlated with a high photolysis quantum yield. Our study on the biocompatible photocage reveals fundamental insight for designing advanced photocages such as longer wavelengths in different solvent conditions tailored for applications in basic and applied research.
Highlights
IntroductionTo be compatible with advanced biomedical research, efficient photocages should feature high-yielding photolysis, which implies high extinction coefficients and photolysis quantum yields
We reveal that the nature of the excited state is strongly solvent dependent
(1a) was modified with an acetyl group to produce (1b) in order to characterize the excited state of the photocage and to determine the rate of photolysis.[15]
Summary
To be compatible with advanced biomedical research, efficient photocages should feature high-yielding photolysis, which implies high extinction coefficients and photolysis quantum yields. Absorption wavelengths at 500 nm or higher are increasingly demanded. Longer wavelengths are less mutagenic to biological cells,[5] reach deeper into biological tissues,[11] and help create scope for using a second orthologous photocage.[11] Synthetic strategies to increase the absorption wavelength are to add auxochromes,[12,20] extend the conjugated system,[13] substitute oxygen in carbonyls or lactones,[14] and combinations thereof.[13] Yet, achieving long
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