Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions
Binol quinone methides (BQMs) can be generated from 1,1′-(2,2′-dihydroxy-1,1′-binaphthyl-6,6′-diyl)bis(<i>N</i>,<i>N</i>,<i>N</i>-trimethylmethanamiuium) bromide (BQMP-b) in a 1:1 MeCN:H<sub>2</sub>O mixed soluti...
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MDPI AG
2018-11-01
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| Series: | Molecules |
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| author | Zhiping Yan Lili Du Xin Lan Yuanchun Li Wenchao Wang David Lee Phillips |
| author_facet | Zhiping Yan Lili Du Xin Lan Yuanchun Li Wenchao Wang David Lee Phillips |
| author_sort | Zhiping Yan |
| collection | DOAJ |
| description | Binol quinone methides (BQMs) can be generated from 1,1′-(2,2′-dihydroxy-1,1′-binaphthyl-6,6′-diyl)bis(<i>N</i>,<i>N</i>,<i>N</i>-trimethylmethanamiuium) bromide (BQMP-b) in a 1:1 MeCN:H<sub>2</sub>O mixed solution via a ground state intramolecular proton transfer (GSIPT), as mentioned in our previously reported studies. Here, the photoreaction of BQMP-b in neutral and basic aqueous solution (pH = 7, 10, 12) was investigated to explore the possible mechanisms and the key intermediates produced in the process of the photoreaction and to examine whether they are different from those in a neutral mild-mixed MeCN:H<sub>2</sub>O solution. The studies were conducted using femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman spectroscopy (ns-TR<sup>3</sup>) in conjunction with results from density functional theory (DFT) computations. The results showed that BQMP-b was deprotonated initially and produced BQMs species more effectively through an E1bc elimination reaction in a strong basic aqueous condition (pH = 12), which differed from the reaction pathway that took place in the solution with pH = 7 or 10. A related single naphthol ring molecule 1-(6-hydroxynaphthalen-2-yl)-<i>N</i>,<i>N</i>,<i>N</i>-trimethylmethanaminium bromide (QMP-b) that did not contain a second naphthol ring was also investigated. The related reaction mechanisms are elucidated in this work, and it is briefly discussed how the mechanisms vary as a function of aqueous solution pH conditions. |
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| spelling | doaj.art-c528bf68229a4319b823aa0232787ab22022-12-21T23:35:16ZengMDPI AGMolecules1420-30492018-11-012312310210.3390/molecules23123102molecules23123102Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous SolutionsZhiping Yan0Lili Du1Xin Lan2Yuanchun Li3Wenchao Wang4David Lee Phillips5Department of Chemistry, The University of Hong Kong, Hong Kong, ChinaDepartment of Chemistry, The University of Hong Kong, Hong Kong, ChinaDepartment of Chemistry, The University of Hong Kong, Hong Kong, ChinaDepartment of Chemistry, The University of Hong Kong, Hong Kong, ChinaDepartment of Chemistry, The University of Hong Kong, Hong Kong, ChinaDepartment of Chemistry, The University of Hong Kong, Hong Kong, ChinaBinol quinone methides (BQMs) can be generated from 1,1′-(2,2′-dihydroxy-1,1′-binaphthyl-6,6′-diyl)bis(<i>N</i>,<i>N</i>,<i>N</i>-trimethylmethanamiuium) bromide (BQMP-b) in a 1:1 MeCN:H<sub>2</sub>O mixed solution via a ground state intramolecular proton transfer (GSIPT), as mentioned in our previously reported studies. Here, the photoreaction of BQMP-b in neutral and basic aqueous solution (pH = 7, 10, 12) was investigated to explore the possible mechanisms and the key intermediates produced in the process of the photoreaction and to examine whether they are different from those in a neutral mild-mixed MeCN:H<sub>2</sub>O solution. The studies were conducted using femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman spectroscopy (ns-TR<sup>3</sup>) in conjunction with results from density functional theory (DFT) computations. The results showed that BQMP-b was deprotonated initially and produced BQMs species more effectively through an E1bc elimination reaction in a strong basic aqueous condition (pH = 12), which differed from the reaction pathway that took place in the solution with pH = 7 or 10. A related single naphthol ring molecule 1-(6-hydroxynaphthalen-2-yl)-<i>N</i>,<i>N</i>,<i>N</i>-trimethylmethanaminium bromide (QMP-b) that did not contain a second naphthol ring was also investigated. The related reaction mechanisms are elucidated in this work, and it is briefly discussed how the mechanisms vary as a function of aqueous solution pH conditions.https://www.mdpi.com/1420-3049/23/12/3102bifunctional quinone methidestime-resolved resonance RamanDFT calculationE1bc elimination reaction |
| spellingShingle | Zhiping Yan Lili Du Xin Lan Yuanchun Li Wenchao Wang David Lee Phillips Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions Molecules bifunctional quinone methides time-resolved resonance Raman DFT calculation E1bc elimination reaction |
| title | Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions |
| title_full | Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions |
| title_fullStr | Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions |
| title_full_unstemmed | Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions |
| title_short | Time-Resolved Spectroscopic and Density Functional Theory Investigation of the Photogeneration of a Bifunctional Quinone Methide in Neutral and Basic Aqueous Solutions |
| title_sort | time resolved spectroscopic and density functional theory investigation of the photogeneration of a bifunctional quinone methide in neutral and basic aqueous solutions |
| topic | bifunctional quinone methides time-resolved resonance Raman DFT calculation E1bc elimination reaction |
| url | https://www.mdpi.com/1420-3049/23/12/3102 |
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