Phototriggers, sometimes called photocages or photoremovable protecting groups, have been prove to be a powerful and efficient tool for releasing biological small molecules and drugs with high spatial and temporal resolution. The photorelease of caged moieties is commonly induced by one-photon excitation of UV or near-UV light. But the potential damage of UV higher energy to the biological system greatly limits the development of one-photon phototriggers. Recently, there are more and more interests attracted to some special phototriggers with large enough two photon excitation cross sections. Dore and his colleagues have discoveries the quinoline-derived compounds are a kind of much promising phototriggers with sensitivity toward 2-photon excitation. Meanwhile, the investigation of reaction mechanism of photoreleasing is becoming more important because it can not only help clarify the reaction steps and transient species, but also provide more guidance in improving the design of two-photon phototriggers. In this study, the newly synthesized 8-cyano-7-hydroxyquinoline caged triethylamine (1) is investigated through a broad range of time-resolved techniques including femtosecond transient absorption and emission spectroscopy, nanosecond transient absorption spectroscopy, transient Raman spectroscopy. Moreover, a combination of density functional calculation analysis and spectroscopic experiments is used to trace essentially the complete behavior of photochemistry and photophysics of this phototriggers, and allow us to have a first look at the intersystem crossing between the excited singlet and triplet carbocation. It can be concluded that the photolytic heterolysis of the carbon-amine leaving group for phototrigger 1 has been demonstrated to take place in the singlet excited state, resulting in the ultrafast photorelease of the leaving group with an estimated time constant of ~70 ps. The advantage of the ultrafast photorelease significantly enhances the potential of the quinoline caged triethylamine compound in mediating a much quicker release of physiologically active messengers through two-photon excitation.

Ultrafast photoreleasing of the quinoline-derived phototrigger with sensitivity toward 2-photon excitation

253rd National Meeting (2017)

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