Dr. David Philips, University of Hong Kong
Host: Dr. Winter
"Time-Resolved Spectroscopic Studies of Selected Photodeprotection Compounds and Insight into Their Reaction Mechanisms"
Time-resolved spectroscopy methods like femtosecond transient absorption (fs-TA) and picosecond time-resolved resonance Raman (ps-TR3) spectroscopy and others are very powerful tools to directly observe and characterize the electronic excited states and reactive intermediate in many kinds of photorelease systems. For example, these time-resolved methods were applied to study the photodeprotection and rearrangement reactions for the pHP phototrigger compounds p-hydroxyphenacyl diethyl phosphate (HPDP) and diphenyl phosphate (HPPP) in which fs-TA spectroscopy was used to observe the dynamics of the triplet precursor decay as well as to study the influence of the solvent and leaving group on the triplet quenching process.[1,2] Ps-TR3 spectroscopy was used to directly monitor the formation dynamics for the photosolvolytic rearrangement product and its solvent and leaving group dependence.[1,2] The TA and TR3 spectroscopy experiments were also used to characterize the structural and electronic properties of the triplet precursor to the HPDP and HPPP deprotection reactions.[1,2] These results combined with our previous study on the photophysical events occurring on the early picosecond time scale (see reference 1 below) provide a real time overall mechanistic description for the photodeprotection and rearrangement reactions of pHP caged phosphate phototrigger compounds.[1,2] Similar time-resolved spectroscopy results were also successfully utilized for benzoin based phototrigger compounds [3,4] and selected tertiary amines linked to the 8-cyano-7-hydroxyquinolinyl (CyHQ) photoremovable protecting group (PPG)  that could provide efficient release of bioactive molecules through 1- and 2-photon excitation (1PE and 2PE). Time-resolved spectroscopy investigations of the photorelease of OH radicals from blebbistatin in aqueous environments via one photon blue light or two photon near infrared light excitation and their potential for use in photochemically activated cancer therapy (PCAT) was also characterized by our group recently.
 C. Ma, W. M. Kwok, W. S. Chan, P. Zuo, J. T. W. Kan, P. H. Toy and D. L. Phillips*, J. Am. Chem. Soc. 127, 1463-1472 (2005).
 W. M. Kwok, C. Ma, W. S. Chan, J. T. W. Kan, P. H. Toy and D. L. Phillips*, J. Am. Chem. Soc. 128, 2558-2570 (2006).
. C. Ma, Y. Du, W. M. Kwok and D. L. Phillips*, Chem. Eur. J. 13, 2290-2305 (2007).
 C. S. Ma, W. M. Kwok, H. Y. An, M. Y. Fu, P. H. Toy and D. L. Phillips*, Chem. Eur. J. 16, 5102-5118 (2010).
 N. Asad, D. Deodato, X. Lan, M. B. Widegren, D. L. Phillips,*L. L. Du* and T. M. Dore* J. Am. Chem. Soc. 139,12591–12600 (2017).
 M.-D. Li*, N.-K. Wong, J. Xiao, R. X. Zhu, L. L. Wu, S. Y. Dai, F. Chen, G. H. Huang, X. Y. Bai, M. R. Geraskina, A. H. Winter, X. B. Chen*, Y. X. Liu, W. H. Fang, D. Yang*, D. L. Phillips*,
J. Am. Chem. Soc. 140, 15957-15968 (2018).