1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

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3 Discussion and Results utilization of equation (1), contemplating the maxima of a specific Q-band in tautomers A and B. 56 ln(1/r AB ) 𝑟 �� = 𝑂𝐷 �� [𝑄 �(0,0)] 𝑂𝐷 �� [𝑄 �(0,0)] (1) At 240 K (-33 °C), 𝑟 �� equals 12 while at room temperature it is determined to be 4. Thus, by lowering the temperature, tautomer A becomes more and more predominant. Based on theoretical studies, tautomeric structure T1 (Scheme 33) is considered to be of lower energy (thermodynamically more stable) and should hence be assigned tautomer A. To really deliver solid proof, further investigations will have to be conducted as already mentioned. Nevertheless, it is possible to deduce the energetic difference for the NH-tautomers ∆𝐸 �� (in the ground state, analogous for exited states ∆𝐸 ��) from the temperature dependent spectra in accordance to VAN’T HOFF’s theory using equation (2), in which the ratio 𝑟 �� is referred to and 𝐶 represents a constant, 𝑘 � BOLTZMANN’s constant and 𝑇 the temperature in K. 𝑙𝑛 � 𝑂𝐷 �� [𝑄 �(0,0)] 1 �=𝑙𝑛� � =𝐶− 𝑂𝐷 �� [𝑄 �(0,0)] 𝑟 �� ∆𝐸 �� 𝑘 �𝑇 (2) The corresponding VAN’T HOFF-plot is shown in Figure 23. -1.5 -2.0 -2.5 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2 1/T [10-3 K-1 ] Figure 23. Temperature dependency of 𝑟 ��of tautomers A and B of 53. Finally, we were able to construct a potential diagram depicting possible conversions and potential barriers being shown in Figure 24. Hence is to be concluded, that the potential barrier for the conversion A → B is higher in the S1 state than in the ground state S0. Therewith, a photoinduced conversion from A to B by selective excitation of A is not possible.
S1 S0 0 0 h − �� ℎ𝜈 � ν T1 Tautomer A ΔES1 ΔES0 Tautomer B 0 0 h − �� ℎ𝜈 � ν T2 Discussion and Results 3 Figure 24. Postulated energy diagram depicting the S0 and S1 states of tautomers A and B of 53 based on calculated values. Furthermore displayed: lowest energy transitions and energy differences for both states. The temperature dependent equilibrium of A and B was used as basis. 3.2.3.4.3 Transient Absorption Spectroscopy on ps-Level (ps-TAS) To get further insight into the compound’s behavior concerning relaxation by IC or ISC, ps- TAS – a pump-probe method – could be utilized to investigate the dynamics of ground state repopulation after photoexcitation and depopulation of the first excited state S1 via time dependent changes in the absorption behavior. 96,109 These measurements furnished fluorescence life-times and values for the ISC quantum yield (ΦISC). Together with the already determined fluorescence quantum yield (Φfl), the quantum yield for IC (ΦIC) can be obtained using equation (3). Φ f� + Φ ISC + Φ IC = 1 (3) For compound 53, the measurements result in a ΦISC value of 0.88 (± 0.03) being quite high compared to other porphyrin structure like e.g. pyropheophorbide a 33 (ΦISC = 0.52) 86 or TPP 15 (ΦISC = 0.68). Therewith, ΦIC for 53 can be determined to 0.09 (± 0.04). To explain this enhanced ISC transition, one has to take into account that the macrocyclic π- system is being distorted. That feature should have a significant impact on the spin-orbit coupling in such systems leading to the observed effect. A verification of that assumption S1 S0 57
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Semi-Natural and Synthetic Chiral C
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Die vorliegende Arbeit entstand in
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Table of Contents 1 Introduction 1
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n J j-coupling (constant) with n in
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1 Introduction characteristics. For
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1 Introduction 1.1 Porphyrins - A G
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3 Discussion and Results correspond
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3 Discussion and Results The remain
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3 Discussion and Results 3.2.8.1 Us
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3 Discussion and Results nitro comp
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3 Discussion and Results The effect
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3 Discussion and Results 3.2.9 Pote
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3 Discussion and Results peak at m/
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3 Discussion and Results Table 25.
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4 Summary As the characterization d
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5 Zusammenfassung 5 Zusammenfassung
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5 Zusammenfassung Da in guten Ausbe
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6 Experimental Section UV/Vis spect
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6 Experimental Section 6.2 Studied
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6 Experimental Section 13 C NMR (10
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6 Experimental Section (cyanomethyl
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6 Experimental Section 6.2.4 AB3-Ty
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6 Experimental Section EA: C57H56N4
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6 Experimental Section 6.2.5 A2B2-T
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6 Experimental Section 6.2.5.5 αβ
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6 Experimental Section 6.2.5.9 αα
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6 Experimental Section UV/Vis (CH2C
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6 Experimental Section broad signal
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7 References 16 H. Fischer, K. Zeil
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7 References 57 S. Schwartz, K. Abs
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7 References 89 (a) R. C. Fuson, J.
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7 References 131 (a) J. Perdew, Phy
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S. Jasinski, N. Jux, “Investigati
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Ein großer Dank gilt auch den Ange
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Cirruculum vitae Stefan Jasinski Ge
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1.1 Porphyrins - Friedrich-Alexander-Universität Erlangen-Nürnberg

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