the reaction can in principle act similarly to a spectrally broad optical pulse. For ET to the solvent, Scholeset al., observed all three kinds of VWP.92 The optical pulse generates VWP on the reactant surface which act as spectator modes and survive ET without dephasing. In addition, the coherence of high-frequency VWP relevant to the ET reaction coordinate are lost during ET reaction, attributed to the multiple kinetic pathways as discussed in the Bixon-Jortner model.91A third type of VWP was found, that is only visible in the product state, has no coun-terpart in the reactant state and can be correlated to low-frequency modes. They explain their observation by partitioning the reaction coordinate in two quantum degrees of freedom: a low-frequency mode that is coherently excited and a high-frequency mode along which the reaction occurs and which looses coherence upon ET. Both, coordinates change their equilibrium geometry from reactant to product similar to the classical Sumi-Marcus model,94that describes ET with a slow and a fast coordinate. Upon ET along the, kinetically favoured, faster high-frequency mode, the probability distribution along the low-frequency vibration is produced in a non-equilibrium position. The ballistic ET acts similarly to an impulsive light pulse and triggers VWP along the low-frequency coordinate. Quantum mechani-cally, the stationary vibrational wavefunction of the reactant state is mapped onto multiple vibrational levels on the product state, similarly to the GS wavefunction which is mapped onto multiple ES vibrational wavefunctions by an impulsive ex-citation pulse. We invoke a similar mechanism for VWP impulsively triggered by ultrafast intramolecular PET in paper I.
1.9 Outline of the thesis
This thesis is cumulative. The main parts are therefore the peer-reviewed pub-lications and submitted manuscripts reprinted in chapters 3-6. The supporting informations for the manuscripts are given in the appendix.
These chapters are preceded by the experimental Chapter 2 that highlights the instrumental developments achieved during this doctoral work. Furthermore, stan-dard operating procedures and alignment steps are explained. The main learnings from the thesis are shortly summarized in Chapter 7.
References
1. Herbst, W.; Hunger, K.Industrial Organic Pigments: Production, Properties, Applications; John Wiley & Sons, 2006.
2. Erk, P.High Performance Pigments; John Wiley & Sons, Ltd, 2001; Chapter 8, pp 103–123.
3. Gissl´en, L.; Scholz, R.Phys. Rev. B 2009,80, 115309.
4. Hestand, N. J.; Spano, F. C.Chem. Rev.2018,
5. Kasha, M.Physical Processes in Radiation Biology; Academic Press, 1964.
6. Kasha, M.; Rawls, H. R.; Ashraf, E.-B. M.Pure Appl. Chem.1965,11, 371–
392.
7. Klebe, G.; Graser, F.; H¨adicke, E.; Berndt, J.Acta Crystallogr. B 1989, 45, 69–77.
8. Graser, F.; H¨adicke, E.Liebigs Ann. Chem.1980,1980, 1994–2011.
9. Graser, F.; H¨adike, E. Liebigs Ann. Chem.1984,1984, 483–494.
10. H¨adicke, E.; Graser, F.Acta Crystallogr. A1986,42, 189–195.
11. Mizuguchi, J.; Tojo, K.J. Phys. Chem. B 2002,106, 767–772.
12. Scholes, G. D.Annu. Rev. Phys. Chem.2003,54, 57–87.
13. Wasielewski, M. R.Chem. Rev.1992,92, 435–461.
14. Young, R. M.; Wasielewski, M. R.Acc. Chem. Res. 2020,53, 1957–1968.
15. Simpson, W. T.; Peterson, D. L.J. Chem. Phys.1957,26, 588–593.
16. F¨orster, T.Ann. Phys.1948, 437, 55–75.
17. F¨orster, T.Ber. Bunsenges. Phys. Chem.1960,64, 157–165.
18. F¨orster, T.Radiat. Res. Supp.1960,2, 326–339.
19. Roy, R.; Hohng, S.; Ha, T.Nat. Methods 2008,5, 507–516.
20. Stryer, L.Annu. Rev. Biochem. 1978,47, 819–846.
21. Hestand, N. J.; Spano, F. C.Acc. Chem. Res. 2017,50, 341–350.
22. W¨urthner, F.; Kaiser, T. E.; Saha-M¨oller, C. R.Angew. Chem. Int. Ed.2011, 50, 3376–3410.
23. Ghosh, S.; Li, X.-Q.; Stepanenko, V.; W¨urthner, F.Chem. Eur. J.2008,14, 11343–11357.
24. Spano, F. C.Acc. Chem. Res. 2010,43, 429–439.
25. Engels, B.; Engel, V.Phys. Chem. Chem. Phys.2017,19, 12604–12619.
26. v B¨unau, G.Ber. Bunsenges. Phys. Chem.1970,74, 1294–1295.
27. Birks, J. B.; Christophorou, L. G.Spectrochim. Acta 1963, 19, 401–410.
28. Birks, J. B.Nature 1967,214, 1187–1190.
29. Birks, J. B.Rep. Prog. Phys.1975,38, 903–974.
30. Stevens, B.; Hutton, E.Nature 1960,186, 1045–1046.
31. Pensack, R. D.; Ashmore, R. J.; Paoletta, A. L.; Scholes, G. D.J. Phys. Chem.
C 2018,
32. Casanova, D.Int. J. Quantum Chem.2015,115, 442–452.
33. Dover, C. B.; Gallaher, J. K.; Frazer, L.; Tapping, P. C.; Petty, A. J.; Cross-ley, M. J.; Anthony, J. E.; Kee, T. W.; Schmidt, T. W.Nat. Chem.2018,10, 305–310.
34. Liu, H.; Yao, L.; Li, B.; Chen, X.; Gao, Y.; Zhang, S.; Li, W.; Lu, P.; Yang, B.;
Ma, Y.Chem. Commun.2016,52, 7356–7359.
35. Feng, X.; Krylov, A. I.Phys. Chem. Chem. Phys.2016, 18, 7751–7761.
36. Dereka, B.; Rosspeintner, A.; Li, Z.; Liska, R.; Vauthey, E.J. Am. Chem. Soc.
2016,138, 4643–4649.
References 19 37. Dereka, B.; Rosspeintner, A.; Krzeszewski, M.; Gryko, D. T.; Vauthey, E.
Angew. Chem. Int. Ed.2016,55, 15624–15628.
38. Dereka, B.; Koch, M.; Vauthey, E. Acc. Chem. Res.2017,50, 426–434.
39. Dereka, B.; Svechkarev, D.; Rosspeintner, A.; Aster, A.; Lunzer, M.; Liska, R.;
Mohs, A. M.; Vauthey, E.Nat. Commun. 2020,11, 1925.
40. Vauthey, E.ChemPhysChem 2012,13, 2001–2011.
41. Young, R. M.; Wasielewski, M. R. Acc. Chem. Res.2020,53, 1957–1968.
42. Sundstr¨om, V.Annu. Rev. Phys. Chem.2008,59, 53–77.
43. Markovic, V.; Villamaina, D.; Barabanov, I.; Lawson Daku, L. M.; Vauthey, E.
Angew. Chem. Int.Ed.2011, 50, 7596–7598.
44. Dobkowski, J.; Grabowski, Z. R.; Paeplow, B.; Rettig, W.; Koch, K. H.;
M¨ullen, K.; Lapouyade, R.New J. Chem.1994,18, 525–533.
45. Kovalenko, S. A.; P´erez Lustres, J. L.; Ernsting, N. P.; Rettig, W. J. Phys.
Chem. A2003,107, 10228–10232.
46. Piet, J. J.; Schuddeboom, W.; Wegewijs, B. R.; Grozema, F. C.; War-man, J. M.J. Am. Chem. Soc.2001,123, 5337–5347.
47. Coleman, A. F.; Chen, M.; Zhou, J.; Shin, J. Y.; Wu, Y.; Young, R. M.;
Wasielewski, M. R.J. Phys. Chem. C 2020,124, 10408–10419.
48. Kong, J.; Zhang, W.; Li, G.; Huo, D.; Guo, Y.; Niu, X.; Wan, Y.; Tang, B.;
Xia, A.J. Phys. Chem. Lett.2020, 10329–10339.
49. Wu, Y.; Young, R. M.; Frasconi, M.; Schneebeli, S. T.; Spenst, P.; Gard-ner, D. M.; Brown, K. E.; W¨urthner, F.; Stoddart, J. F.; Wasielewski, M. R.
J. Am. Chem. Soc.2015,137, 13236–13239.
50. Cook, R. E.; Phelan, B. T.; Kamire, R. J.; Majewski, M. B.; Young, R. M.;
Wasielewski, M. R.J. Phys. Chem. A2017, 121, 1607–1615.
51. Smith, M. B.; Michl, J.Chem. Rev.2010, 110, 6891–6936.
52. Smith, M. B.; Michl, J.Annu. Rev. Phys. Chem. 2013,64, 361–386.
53. Shockley, W.; Queisser, H. J.J. Appl. Phys.1961,32, 510–519.
54. Reference Air Mass 1.5 Spectra. https://www.nrel.gov/grid/solar-resource/spectra-am1.5.html.
55. Rao, A.; Friend, R. H.Nat. Rev. Mater.2017, 2, 1–12.
56. Sanders, S. N.; Pun, A. B.; Parenti, K. R.; Kumarasamy, E.; Yablon, L. M.;
Sfeir, M. Y.; Campos, L. M.Chem 2019,5, 1988–2005.
57. Wilson, M. W. B.; Rao, A.; Clark, J.; Kumar, R. S. S.; Brida, D.; Cerullo, G.;
Friend, R. H.J. Am. Chem. Soc.2011,133, 11830–11833.
58. Sanders, S. N.; Kumarasamy, E.; Pun, A. B.; Trinh, M. T.; Choi, B.; Xia, J.;
Taffet, E. J.; Low, J. Z.; Miller, J. R.; Roy, X.; Zhu, X.-Y.; Steigerwald, M. L.;
Sfeir, M. Y.; Campos, L. M.J. Am. Chem. Soc.2015,137, 8965–8972.
59. Pensack, R. D.; Tilley, A. J.; Grieco, C.; Purdum, G. E.; Ostroumov, E. E.;
Granger, D. B.; Oblinsky, D. G.; Dean, J. C.; Doucette, G. S.; Asbury, J. B.;
Loo, Y.-L.; Seferos, D. S.; Anthony, J. E.; Scholes, G. D.Chem. Sci.2018,9,
6240–6259.
60. Pensack, R. D.; Ostroumov, E. E.; Tilley, A. J.; Mazza, S.; Grieco, C.; Thor-ley, K. J.; Asbury, J. B.; Seferos, D. S.; Anthony, J. E.; Scholes, G. D.J. Phys.
Chem. Lett.2016,7, 2370–2375.
61. Basel, B. S. et al.Nat. Commun.2017,8, 15171.
62. Basel, B. S.; Zirzlmeier, J.; Hetzer, C.; Reddy, S. R.; Phelan, B. T.; Krzya-niak, M. D.; Volland, M. K.; Coto, P. B.; Young, R. M.; Clark, T.; Thoss, M.;
Tykwinski, R. R.; Wasielewski, M. R.; Guldi, D. M.Chem2018,4, 1092–1111.
63. Tayebjee, M. J. Y.; Sanders, S. N.; Kumarasamy, E.; Campos, L. M.;
Sfeir, M. Y.; McCamey, D. R.Nat. Phys.2017, 13, 182–188.
64. Merrifield, R. E.Pure Appl. Chem.1971,27, 481–498.
65. Margulies, E. A.; Miller, C. E.; Wu, Y.; Ma, L.; Schatz, G. C.; Young, R. M.;
Wasielewski, M. R.Nat. Chem.2016, 8, 1120–1125.
66. Korovina, N. V.; Pompetti, N. F.; Johnson, J. C. J. Chem. Phys.2020,152, 040904.
67. Beckwith, J. S.; Rumble, C. A.; Vauthey, E.Int. Rev. Phys. Chem.2020,39, 135–216.
68. van Stokkum, I. H. M.; Larsen, D. S.; van Grondelle, R. Biochim. Biophys.
Acta 2004,1657, 82–104.
69. Homberg, A.; Lacour, J.Chem. Sci.2020,11, 6362–6369.
70. Poggiali, D.; Homberg, A.; Lathion, T.; Piguet, C.; Lacour, J. ACS Catal.
2016,6, 4877–4881.
71. Vishe, M.; Hrdina, R.; Poblador-Bahamonde, A. I.; Besnard, C.; Gu´en´ee, L.;
B¨urgi, T.; Lacour, J.Chem. Sci.2015,6, 4923–4928.
72. Zeghida, W.; Besnard, C.; Lacour, J.Angew. Chem. Int. Ed.2010,49, 7253–
7256.
73. Angulo, G.; Rosspeintner, A.; Lang, B.; Vauthey, E.Phys. Chem. Chem. Phys.
2018,20, 25531–25546.
74. Schaberle, F. A.; Serpa, C.; Arnaut, L. G.; Ward, A. D.; Karlsson, J. K. G.;
Atahan, A.; Harriman, A.Chemistry 2020,2, 545–564.
75. Al Kobaisi, M.; Bhosale, S. V.; Latham, K.; Raynor, A. M.; Bhosale, S. V.
Chem. Rev.2016,116, 11685–11796.
76. Ling, Q.-H.; Zhu, J.-L.; Qin, Y.; Xu, L.Mater. Chem. Front.2020,4, 3176–
3189.
77. Sakai, N.; Mareda, J.; Vauthey, E.; Matile, S. Chem. Commun. 2010, 46, 4225–4237.
78. ˇSolomek, T.; Powers-Riggs, N. E.; Wu, Y.-L.; Young, R. M.; Krzyaniak, M. D.;
Horwitz, N. E.; Wasielewski, M. R.J. Am. Chem. Soc.2017,139, 3348–3351.
79. Suraru, S.-L.; W¨urthner, F.Angew. Chem. Int. Ed.2014,53, 7428–7448.
80. Ganesan, P.; Baggerman, J.; Zhang, H.; Sudh¨olter, E. J. R.; Zuilhof, H. J.
Phys. Chem. A2007, 111, 6151–6156.
References 21 81. Yushchenko, O.; Licari, G.; Mosquera-Vazquez, S.; Sakai, N.; Matile, S.;
Vau-they, E.J. Phys. Chem. Lett.2015,6, 2096–2100.
82. Miros, F. N.; Matile, S.ChemistryOpen 2016,5, 219–226.
83. Wasielewski, M. R. J. Org. Chem.2006,71, 5051–5066.
84. Bornhof, A.-B.; Bauz´a, A.; Aster, A.; Pupier, M.; Frontera, A.; Vauthey, E.;
Sakai, N.; Matile, S.J. Am. Chem. Soc.2018,140, 4884–4892.
85. Liebel, M.; Schnedermann, C.; Wende, T.; Kukura, P.J. Phys. Chem. A2015, 119, 9506–9517.
86. Buckup, T.; L´eonard, J. In Multidimensional Time-Resolved Spectroscopy; Buckup, T., L´eonard, J., Eds.; Topics in Current Chemistry Collections;
Springer International Publishing: Cham, 2019; pp 207–245.
87. Atkins, P. W.; Friedman, R. S.Molecular Quantum Mechanics; OUP Oxford, 2011.
88. Cina, J. A.; Kovac, P. A.; Jumper, C. C.; Dean, J. C.; Scholes, G. D.J. Chem.
Phys.2016,144, 175102.
89. Jumper, C. C.; Arpin, P. C.; Turner, D. B.; McClure, S. D.; Rafiq, S.;
Dean, J. C.; Cina, J. A.; Kovac, P. A.; Mirkovic, T.; Scholes, G. D.J. Phys.
Chem. Lett.2016,7, 4722–4731.
90. Rafiq, S.; Scholes, G. D. J. Am. Chem. Soc.2019,141, 708–722.
91. Jortner, J.; Bixon, M.J. Chem. Phys.1988,88, 167–170.
92. Rafiq, S.; Fu, B.; Kudisch, B.; Scholes, G. D.Nat. Chem.2020, 1–7.
93. Huber, R.; Dworak, L.; Moser, J. E.; Gr¨atzel, M.; Wachtveitl, J. J. Phys.
Chem. C 2016, 120, 8534–8539.
94. Sumi, H.; Marcus, R. A.J. Chem. Phys.1986, 84, 4894–4914.
CHAPTER 2
Setup development and experimental details
23
2.1 Transient absorption spectroscopy
Transient absorption (TA) spectroscopy is a widely used pump-probe technique where the excited state dynamics of a chemical system can be followed in time.
The chemical process of interest is thereby triggered by exciting the sample with a short laser pulse. A second, spectrally broad laser pulse monitors the photo-induced transmission changes. To determine the absorption change ∆A(λ) photo-induced by the pump pulse, the intensity of two consecutive probe pulses, one with (S∗) and one without excitation (S) of the sample, are compared. Controlling the time difference between pump and probe (∆t), by changing the distance the pump pulse travels in space, gives a two dimensional data matrix:
∆Aexp(∆t,λ) =−log10 whereAis the steady state absorption of the sample and ∆Ais the absorption change due to sample excitation. Only if the intensity of two consecutive probe pulsesIS0(λ) andIS∗(λ) are identical their contribution cancels and the experimen-tally determined ∆Aexpgives the real ∆A. Since the probe light however fluctuates from shot-to-shot, all three TA instruments, which were used in this thesis, use single-shot referencing. The white light generation (WLG) is thereby followed by a beam splitter (BS) dividing the probe beam into a sample and reference channel which is detected on two spectrographs monitoring S(λ) and R(λ), respectively (Figure 2.1B). The two channels are essential to increase the signal-to-noise ratio, since they account for the intensity fluctuations of two consecutive pulses, I∗(λ) andI0(λ):1a If the optical path and the alignment of the spectrograph of the sample and ref-erence path are completely identical, IS∗ = IR∗ and IS0 = IR0 and the dependence on the intensity fluctuations cancel. As will be discussed in section 2.2 and 2.3, decreasing the differences between the two optical pathways is a major experi-mental challenge. In general, single-shot detection is superior as long as the noise introduced by the reference detection and the effect of misalignment between the two channels is smaller than the fluctuations between two consecutive laser pulses.
For a quantitative discussion on the effect of referencing on the signal-to-noise and the impact of referencing refer to an excellent review published recently.1
On a molecular level, the ∆Aoriginates from a photo-population of the excited state triggered by the pump pulse. The population changes are observable as pos-itive and negative features in the TA spectrum (Figure 2.1a). Due to a decrease of the ground state concentration upon excitation, a negative feature can be ob-served at the position of the steady state absorption spectrum, termed ground
aThe ∆tandλdependences are omitted for clarity.
2.1 Transient absorption spectroscopy 25
Figure 2.1: a) Decomposition of the transient absorption (TA) spectrum of TIPS-pentacene in n-hexane. The black line represents the TA spectrum at 100 ps. GSB:
Ground state bleach, SE: Stimulated emission, ESA: Excited state absorption. b) Simpli-fied scheme of a TA instrument using referenced detection. WLG: White light generation;
BS: Beamsplitter.
state bleach (GSB). On the other hand, the population of the excited state and/or formation of new species leads to the appearance of new absorption bands referred to as excited state absorption (ESA). If the populated excited state possesses a significant transition dipole moment to the ground state a second negative signal can be observed attributed to the stimulated emission (SE). In contrast to time resolved fluorescence, dark states, such as triplet states or ion pairs can also be detected by their ESA and can therefore be followed over time. In the UV-Vis spectral region, where spectral features are usually broad, the three contributions frequently overlap which complicates the analysis.
In this thesis, TA spectra recorded with three different experimental setups are presented: a fs-ps Vis (fs-VIS), a fs-ps near infrared (fs-NIR) and a ps-µs UV-Vis (ps-VIS) TA setup. The fs-VIS and fs-NIR setups share the same pump path, whereas the designs of the fs-VIS and the ps-VIS probe path are identical. As part of this thesis, the UV-Vis detection was optimized and the fs-NIR instrument was developed from scratch. Merging the data of the two spectral windows gives a continuous observation window from 330 nm to 1600 nm as illustrated in Figure 2.1a. In the following, the setup design, standard operating procedures and data processing are described. First the two detection systems are discussed followed by a short description of the fs-ps and ps-µs pump paths. All TA instruments use the output of a Ti:Sapphire system (Solstice Ace,Spectra-Physics), generating pulses centred at 800 nm with a 5 kHz repetition rate and a temporal width of 35 fs. The probe beam is chopped down to a frequency of 1 kHz (MC2000B, with MC1F10A 10 Slot ChopperBlade, 20% duty cycle,Thorlabs) due to the higher readout noise of cameras at 5 kHz.