Exploring Photophysical Transitions and Photochemical Reactions

Delve into the fascinating world of photophysical transitions and photochemical reactions through a collection of images showcasing key concepts such as singlet oxygen, triplet states, proton transfers, and sensitization processes. Gain insights into the intricate mechanisms governing these phenomena in chemistry research.

• Photophysical Transitions
• Photochemical Reactions
• Chemistry Research
• Singlet Oxygen
• Triplet States

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1. Elementary Photophysical Transitions and Photochemical Reactions NSF REU June 09, 2023 1

2. Photochemistrys Icons Why I am here. From Photochemistry of Organic Compounds by Peter Kl n and Jakob Wirz, 2009 2

3. Photo by Lilli Kasha ca. 1970 3

4. Intersystem Crossing Demchenko, A. P. et al.Angew. Chem. Int. Ed. 2014, 53, 2-11. 4

5. Phosphorescence and the Triplet State Gilbert N. Lewis , M. Kasha J. Am. Chem. Soc. 1944, 66, 2100-2116 Naphthalene phosphorescence triplet energies 5

6. External and Internal Heavy Atom Effects -Chloronaphthalene is yellow in EtI, JCP, 1952 6

7. Singlet O2 in Chemiluminescence and in Triplet Energy Transfer 7

8. Double Proton Transfer in 7-Azaindole Proton Transfer Spectroscopy 8

9. The Blue Daylily and Intramolecular S1 Proton Transfer in Flavonoids 9

10. The Kasha Guitar 10

11. Triplet Sensitization 11

12. Triplet Sensitized Stilbene Photoisomerization The Saltiel Plot Hammond, G. S.; Saltiel, J. J. Am. Soc. Chem.1962-1964. 12

13. The Photostationary State 1 d[ t] dt d[ c] dt [ S*][ t] [ S*][ c] [ c] [ ] [ t] 1t-St + 3S* 3t* 3p* 3p* 1t + (1- )1c 1c-St + 3S* 3t* + 1S* = + = 3 1 1 [ S*][ t] [ p*] 0 k k t d 1 = + ) [ p*] 0 k = 3 1 1 [ S*][ c] (1 k c d 3c* + 1S* = = 3 1 1 [ p*] ) [ p*] ) k k t d 3 1 1 (1 k k c d 1 [ ] (1 [ ] k k t = PSS 1 c 13

14. 62 kcal/mol 57 kcal/mol Vertical Excitation 49 kcal/mol Vertical Excitation 5 kcal/mol 14

15. Nonvertical Triplet Energy Transfer 15

16. H H CH3-CH3 C C Average bond energies C-C 83 kcal/mol C=C 146 kcal/mol bond ~ 63 kcal/mol H H H H H H

17. 17

18. cis- and trans-2-butenes are stable separable isomers. They have the same connectivity and are stereoisomers. Rotation about a double bond occurs only at very high T or following light absorption. bond ~ Eact = 66 kcal/mol 18

19. SpinStates ( ( + + ) ) ( ( ) ) T T T S 19

20. Absorbance 170 nm 217 (21,000) 263 (52,500) 239 (3,400) 256 (8,000) max( ( max) ( )n n max x 10-3, M-1cm-1 28 53 80 86 max, nm Effect of Conjugation 1 2 3 4 294.1 328 348 404 20

21. Molecular Orbital Analysis of the Diels-Alder Reaction The diene is the electron donor and the dienophile is the electron acceptor. The concerted nature of the D-A reaction can be understood by considering the interaction of the HOMO of the diene with the LUMO of the dienophile (Fukui/Kyoto, Woodward/Harvard, Hoffmann/Harvard now Cornell---Nobel prize in Chemistry) 1965 1981 21

22. HOMO LUMO EWG 22

23. Frontier Orbital Control of Diels-Alder Reaction HOMO Donor LUMO Acceptor EWG 23

24. Electrocyclic reactions are stereospecific CH3 CH3 175 oC h CH3 CH3 CH3 h 175 oC CH3 24

25. Thermal reaction CH3 CH3 CH3 H3 C conrotatory Rotation in the same direction leads to a bonding interaction (+ lobe on + lobe or - lobe on lobe). The reaction passes through the same TS in both directions. 25

26. Photochemical reaction CH3 CH3 CH3 h H3 C disrotatory Rotation in opposite directions leads to a bonding interaction (+ lobe on + lobe or - lobe on lobe). The reaction passes through the same TS in both directions. 26

27. NEER PRINCIPLE * Havinga, Tetrahedron, 1973 ct = 0.03, tc = 0.016 hv * | florida state university | | florida state university | Egbert Havinga 1909-1988 * hv small_color_torches-new small_color_torches-new * hv * * Havinga, E.; Schlatmann, J. L. M. A Tetrahedron 1961, 16, 146-152. 27

28. 1,6-Dideuteriohexatrienes ttt-Htd2 in C6D12 ctt-Ht cct-Ht C6D12 x tct 0.44 0.085 0.34 CD3CN x tct 0.54 0.093 0.39 0.014 ttt x ttt 0.245 x ctt cct tct ttt x 0.24 0.058 0.11 Saltiel, J.; Redwood, C. E.; Laohhasurayotin, K.; Samudrala, R. Photochemistry of the 1,6-Dideuterio-1,3,5-hexatrienes in Solution: J. Phys. Chem. A 2018, 122, 8477-8489. 28

29. Havingas NEER Principle PreVit PreVit D D Conform Conform ers ers R R Egbert Havinga 1909-1988 h H O H O H Pro Photocyclization Long (-)cZ(-)c R R h H O H O R H Lumi (+)cZ(+)c R OH Photoisomerization Short h H OH Tachy (+)tZ(-)c 29

30. NPE Conformers | florida state university | | florida state university | t-NPEA t-NPEB small_color_torches-new small_color_torches-new c-NPEA c-NPEB NPE conformers 30

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32. Conformer specific photochemistry in c- and t-NPE 32

33. Fluorescence Emission Spectra of t-NPE as a Function of exc in Ar Outgassed Benzene at 20 oC 1.0 t-NPE/Bz 0.8 | florida state university | | florida state university | Normalized Intensity exc = 320 nm exc = 345 nm exc = 350 nm 0.6 small_color_torches-new small_color_torches-new 0.4 0.2 0.0 330 350 370 390 410 430 450 470 490 510 33 , nm

34. Summary of PCA-SM Mathematical Operations Covariance Matrix Transposed Matrix Spectral Input Matrix x = Number of Components Eigenvalues Diagonalized Matrix Eigenvectors Eigenvector Matrix i = V Si, i =V Si Si = iV + iV Pure Component Spectra SA= AV + AV SB= BV + BV Experimental Spectra Si = iV + iV Pure Component Coefficients A, A and B, B 34

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36. Plot Principal Eigenvectors Standard Deviation 0.125 0.0 0.1 0.2 0.3 0.015 Normalized Intensity 0.065 Stern-Volmer equation: 0.009 = 1 + KSV[Q] 0.005 0.003 -0.055 -0.115 -0.003 -0.175 330 350 370 390 410 430 450 470 490 510 , nm Global Stern-Volmer Plots -0.009 0.0500 Conformer Spectra 0.0775 0.1050 3.0 1.0 t t- -NPE/PCA NPE/PCA- -SM SM t-NPEA t-NPEB Normalized Intensity 0.8 t-NPEA 2.0 t-NPEB 0.6 o 0.4 1.0 Global Stern-Volmer equation: 0.2 A[Q] F0( )/F( )= 1 + KSV 0.0 -0.0004 0.0013 0.0030 0.0046 0.0063 0.0080 [O2]/M0.0 36 330 350 370 390 410 430 450 470 490 510 , nm

37. Stern-Volmer Quenching Equation Rate 1A + h exc 1A* Ia 1A* 1A + h f kf[1A*] kis[1A*] 1A* 3A* kp[1A*] 1A* P kq[Q][1A*] 1A* + Q 1A + Q* 37 S-V Kinetics

38. The Stern-Volmer Plot 1 d[ ] h k d[ ] h = = = o f f f k f= 1 k [ A*] f + + I dt k k k f dt 1 a f is p d[ A*] = + + 0 = 1 I ( )[ A*] k k k where Ia is the rate of light absorption a f is p dt I k = 1 [ A*] a k k + + k k = = f k f f is p f + + + + [Q] 1 k k k k [Q] f is p q q d[ ] I h k = f f a + + ( dt k k k f is p ) 1 = + [Q] 1 = + o f / [Q] k K f q SV 38

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40. Benzophenone State Diagram 40

41. El-Sayeds Rules for Intersystem Crossing 41

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46. Multidimensional Isomerization Conical Intersections Trapping Twisted Intermediates ?? ? ? ?? ???? ?????= ?? ?? ????? B. G. Levine, T. J. Mart nez. Annu. Rev. Phys. Chem. 2007, 58, 613-34. Saltiel, J.; Gupta, S. Photochemistry of the Stilbenes in Methanol. Trapping the Common Phantom Singlet State. J. Phys. Chem. A2018, 122, 6089-6099. 46

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48. Acknowledgments PCA-SM C. Redwood L. Zimanyi Experimental Gosia Bayda, Shipra Gupta Sumesh Krishnan Support NSF (1965-2020) 48

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