A Theoretical Investigation of p-Hydroxyphenacyl Caged Phototrigger Compounds: An Examination of the Excited State Photochemistry of p-Hydroxyphenacyl Acetate
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- 作者：Xuebo Chen ; Chensheng Ma ; Wai Ming Kwok ; Xiangguo Guan ; Yong Du ; David Lee Phillips
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：November 16, 2006
- 年：2006
- 卷：110
- 期：45
- 页码：12406 - 12413
- 全文大小：217K
- 年卷期：v.110,no.45(November 16, 2006)
- ISSN：1520-5215
文摘
Ab initio and density functional theory methods were employed to study the excited states and potentialenergy surfaces of the p-hydoxyphenacyl acetate (HPA) phototrigger compound. Complete active space (CAS)ab initio calculations predicted adiabatic electronic transition energies for the HPA-T1(3n
*), HPA-T2(3*),HPA-S1(1n*), HPA-T3(3n*), HPA-S2(1n*), HPA-S3(1*) 
HPA-S0 transitions that were similar to andin agreement with those found experimentally for closely related aromatic ketones such as p-hydroxyacetophenone and results from similar calculations for other related aromatic carbonyl systems. The 
or 
bond cleavage reactions from the S1 excited state were both found to have relatively high barriers to reaction,and the S1, T1, and T2 states are close in energy with the three S1(1n*), T1(3n*), and T2(3*) surfacesintersecting at the same region. The calculations suggest that intersystem crossing (ISC) can occur very fastfrom the S1 state to the nearby triplet states. This is consistent with results from ultrafast spectroscopyexperiments that observe the S1 state ISC occurs within about 1-2 ps to produce a triplet state for HPA andrelated pHP compounds. The and bond cleavage reactions for the T1 state of HPA are both predicted tohave fairly high barriers and compete with one another. However, this is not completely consistent withexperiments that observe the photodeprotection reactions (e.g. the bond cleavage) of HPA and some otherpHP phototriggers in largely water containing solvents are predominant and occur very fast to release theleaving group. Comparison of the computational results with experimental results for HPA and related pHPcompounds suggests that water molecules likely play an important part in changing the triplet state bondcleavage so that it becomes the predominant pathway and occurs very fast to give an efficient deprotectionreaction. The results reported here provide new insight into the photophysics, reaction pathways, andphotochemistry of the p-hydoxyphenacyl acetate and related pHP caged phototrigger compounds and alsoprovide a benchmark for further and more sophisticated investigations in the future.
*), HPA-T2(3*),HPA-S1(1n*), HPA-T3(3n*), HPA-S2(1n*), HPA-S3(1*) HPA-S0 transitions that were similar to andin agreement with those found experimentally for closely related aromatic ketones such as p-hydroxyacetophenone and results from similar calculations for other related aromatic carbonyl systems. The or bond cleavage reactions from the S1 excited state were both found to have relatively high barriers to reaction,and the S1, T1, and T2 states are close in energy with the three S1(1n*), T1(3n*), and T2(3*) surfacesintersecting at the same region. The calculations suggest that intersystem crossing (ISC) can occur very fastfrom the S1 state to the nearby triplet states. This is consistent with results from ultrafast spectroscopyexperiments that observe the S1 state ISC occurs within about 1-2 ps to produce a triplet state for HPA andrelated pHP compounds. The and bond cleavage reactions for the T1 state of HPA are both predicted tohave fairly high barriers and compete with one another. However, this is not completely consistent withexperiments that observe the photodeprotection reactions (e.g. the bond cleavage) of HPA and some otherpHP phototriggers in largely water containing solvents are predominant and occur very fast to release theleaving group. Comparison of the computational results with experimental results for HPA and related pHPcompounds suggests that water molecules likely play an important part in changing the triplet state bondcleavage so that it becomes the predominant pathway and occurs very fast to give an efficient deprotectionreaction. The results reported here provide new insight into the photophysics, reaction pathways, andphotochemistry of the p-hydoxyphenacyl acetate and related pHP caged phototrigger compounds and alsoprovide a benchmark for further and more sophisticated investigations in the future.