The last learning of the thesis was the solvent dependence of ultrafast reactions occurring on the sub-ps time-scale. In contrast to SB-CS in the perylene dimer, both, the ultrafast PET in the NDI based dyads (Papers I and II) and the SF in close contact conformers (Paper IV) have in common, that they both do not show a significant dependence on the solvent polarity or solvation dynamics. A structural coordinate therefore acts as reaction coordinate and its relaxation along this coordinate is the rate limiting parameter.
For the perylene dimer, the solvation energy is needed to bring the CSS state below the LES due to the nearly isoenergetic energy of the CSS and LES. This explains why the solvent coordinate is crucial for SB-CS in this system. At the excimer geometry, even in high polarity solvents such as acetonitrile, the solvation energy is not sufficient to bring the CSS state well below the LES.
On the other hand, in the NDI dyads already the motion along the structural coordinate is sufficient and CSS can occur entirely along the intramolecular co-ordinate. This observations show that, whether the solvation coordinate plays a significant role, in strongly coupled systems, depends on the driving force of the reaction and is therefore system dependent.
CHAPTER 8
Appendix
89
Lifetime broadening and impulsive generation of vibrational coherence triggered by ultrafast electron transfer.
Alexander Aster, Anna-Bea Bornhof, Naomi Sakai, Stefan Matile, and Eric Vauthey⇤
Electronic Supplementary Information
Contents
S1 Synthesis . . . S2 S2 Experimental details, spectroscopy . . . S3 S2.1 Chemicals . . . S3 S2.2 Absorption . . . S3 S2.3 Transient absorption . . . S3 S2.4 Quantum-chemical calculations . . . S3 S3 Estimation of the driving force . . . S4 S4 Bandshape analysis of the absorption spectra . . . S5 S5 Multiexponential fit of the the local excited state dynamics . . . S6 S6 Position of the the charge-separated state TA band . . . S7 S7 Wavepacket analysis . . . S8 S8 Assignment of the oscillation to a normal mode . . . .S11 S9 Time-dependent density functional theory (TD-DFT) calculations . . . .S12 S9.1 TD-DFT ofIVa. . . .S12 S9.2 Geometry optimization of the S1and S2states. . . .S12 S10 Appendix . . . .S14
S1
S1 Synthesis
Abbreviations.AcOH: Acetic acid; DMF: N,N-Dimethylformamide; equiv.: Equivalents; EtOAc: Ethyl acetate;
min: Minutes; Mp: Melting point; NDA: 1,4,5,8-Naphthalenetetracarboxylic dianhydride; PE: Petroleum ether;
rt: Room temperature; TEA: Triethylamine; TOL: Toluene.
As stated in literature,1reagents for synthesis were purchased from Sigma-Aldrich, Fluka, Acros, Apollo Sci-entific and Bachem. Unless stated otherwise, column chromatography was carried out on silica gel 60 (SilicaFlash P60, 40-63µm). Analytical thin layer chromatography (TLC) was performed on silica gel 60 (Merck, 0.2 mm).
Melting points were measured on a Melting Point M-565 (BUCHI).1H and13C spectra were recorded on a Bruker 500 MHz spectrometer and are referenced to residual solvent peaks and reported as chemical shifts ( ) in ppm relative to TMS ( = 0). Spin multiplicities are reported as a singlet (s), doublet (d), triplet (t), quartet (q) and multiplet (m) with coupling constants (J) given in Hz. 1H and13C resonances were assigned with the aid of additional information from 1D and 2D NMR spectra (H, H-NOESY, H, H-COSY, DEPT 135, HSQC and HMBC). HR ESI-MS for the characterization of new compounds were performed on a Waters Xevo G2-S Tof and are reported as mass-per-charge ratiom/zcalculated and observed.
N
CompoundspNDI,2Ia,3IIa,2IIs4andIVs4are known compounds and their NMR spectra were in agreement with the literature.
General procedure for NDI monomers. A suspension of NDA (1 equiv., 0.1 M), amineA1(1 equiv.), TEA (1 equiv.) in TOL/DMF 2:1 was heated to 110 C for 30 min. under inert atmosphere. AcOH (2 equiv.) and respective aminesA2,A3orA4(1 equiv.) were added and the reaction was heated to 120 C for 2 more hours. The solvent was evaporated. Column chromatography yielded the respective symmetric and asymmetric NDIs as pale yellow solids.
Compounds IIIs and IIIa. Column chromatography CH2Cl2/EtOAc (0-10%) yielded NDIIIIsand NDI IIIain 1% and 32%, respectively.
NDIIIIs:Rf(Pentane/EtOAc 4:1) 0.1, Mp: >300 C;1H NMR (500 MHz, CDCl3): 8.87 (s, 4H), 7.54 – 7.46 (m,
Compound IVa.Column chromatography PE/EtOAc (0-20%) yielded NDIIVain 31%.
NDIIVa: Rf(Pentane/EtOAc 4:1) 0.6, Mp: 182-183 C;1H NMR (500 MHz, CDCl3): 8.83 (d,3J(H,H) = 7.6
8.1 Paper I - Supporting Information 91
S2 Experimental details, spectroscopy S2.1 Chemicals
Acetonitrile (ACN, Roth, 99.9%), methylcyclohexane (MHX, Roth, 99%).
S2.2 Absorption
Absorption spectra were measured on a Cary 50 spectrometer.
S2.3 Transient absorption (TA)
A detailed description of the general principle of the fs-ps TA applying referenced detection using two spectrographs is presented elsewhere.5The experimental setup was the same as that described earlier,6except that all lenses, after white light generation, were replaced by spherical mirrors to prevent chromatic aberration.
Probing was achieved using white light pulses generated by focusing the 800 nm pulses of the Ti:Sapphire amplified system (Spectra Physics, Solstice Ace) in a CaF2plate. Excitation was performed using 375 nm pulses generated by doubling the 750 nm output a TOPAS-Prime in combination with a NirUVis frequency mixer (both from Light Conversion), which were themselves seeded by the output of the Ti:Sapphire amplified system. Before doubling the visible pulses are compressed by a folded prim compressor consisting of two BK7 prisms to optimize the time resolution at the sample.
The samples were measured in a flow cell with a 0.4 mm internal thickness and 200µm windows giving a wavelength dependent instrument response function (IRF) of about 50-200 fs (FWHM of optical Kerr e↵ect (OKE)). The transient absorption signal was checked prior to the experiment to scale linearly with the pump intensity and the absorption spectra of all samples before and after the transient absorption experiments showed no sign of degradation. The polarization of the pump pulses was set to magic angle relative to the white-light pulses.
Data treatment
The pixel to wavelength conversion was achieved using a standard containing rare earth metals (holmium oxide) which shows narrow bands from the UV to the visible spectral region. All transient absorption spectra were cor-rected for background signals showing up before time zero (e. g. spontaneous emission).
The fs-ps spectra were corrected for the dispersion due to the optical chirp using the optical Kerr e↵ect.7
S2.4 Quantum-chemical calculations
Quantum-chemical calculations were performed at the density functional theory (DFT) level. Ground-state cal-culations were carried out with the B3LYP functional and the 6-311++G(d,p) basis set. Time-dependent DFT calculations were performed using the CAM-B3LYP functional and 6-31G(d,p) basis set. All calculations were done using the Gaussian 16 package.8
S3
S3 Estimation of the driving force
The free energy of a photoinduced charge separation (CS) process is given by:9
GCS= ES1+e(Eox(D) Ered(A)) +C (S1)
whereEox(D) andEred(A) are the oxidation and reduction potentials of the donor and acceptor, respectively,ES1
is the energy of the bright excited state andCis a correction factor accounting for the Coulombic interactions.
The driving force ( GCS) for compounds II-IVestimated from the above equation upon neglectingCare listed in Table S1. Unfortunately, no oxidation potential for acetophenone could be found in literature and GCSis expected to be between 0 and 0.35 eV.
Table S1: Estimation of the driving force ( GCS) based on literature values of the oxidation (Eox) and reduction potential (Ered) of donor and acceptor, respectively as well as the energy of the⇡-⇡⇤state of the NDI core (ES1).
Compound Ered(A) / V vs. SCE Eox(D) / V vs. SCE ES1/ eV A-Dn GCS/ eV
Benzene (D) 2.4810 II -0.35
Toluene (D) 2.2811 III -0.55
Mesitylene (D) 1.9811 IV -0.85
NDI (A) -0.4312 3.2612
S4
8.1 Paper I - Supporting Information 93
S4 Bandshape analysis of the absorption spectra
To find out whether the broadening of the S1 S0 band observed by going frompNDIto the dyads can be explained by an ultrashort excited-state lifetime, the following function was fitted to the absorption spectrum of the dyads:
F(¯⌫) =SpNDI(¯⌫)⌦L(¯⌫), (S2) whereSpNDI(¯⌫) is the S1 S0absorption band ofpNDI,⌦designates the convolution andL(¯⌫) is a Lorentzian broadening function centred at ¯⌫0:
L(¯⌫) =1
⇡
1 2 ⌫¯L
(¯⌫ ¯⌫0)2+ (12 ¯⌫L)2, (S3) with ¯⌫Lthe full width at half maximum. Figure S2 illustrates the best fit of eq.S2 to the absorption spectrum of the dyads in ACN.
Ia IIa IIs
IIIa IIIs
IVa IVs
Lorentzian
pNDI
Fit (Convolution of pNDI and Lorentzian) Data
Figure S2: Electronic absorption spectra of the dyads in ACN together with the best fits of eq.S2, and the corresponding Lorentzian broadening functions.
If we assume that the additional broadening observed when going from pNDI to the dyads is entirely due to the ultrashort excited-state lifetime of the dyads, the full width at half maximum of the Lorentzian function is:
¯
⌫L= 1 2⇡cT1
, (S4)
whereT1is the excited-state lifetime. The width of the Lorentzian broadening function, together with the correspondingT1values and the experimentalh⌧ivalues are listed in Table S2.
S5
Table S2: Full widths at half maximum ofL( ¯⌫) obtained from the fit of eq.S2 to the absorption spectra of the dyads in ACN,T1values from eq.S4 and experimentalh⌧ivalues.
Dyad ⌫¯L/ cm 1 T1/ fs h⌧i/ fs
Ia 7 780 206
IIa 30 176 100
IIs 66 80 55
IIIa 33 160 118
IIIs 79 67 59
IVa 88 60 66
IVs 194 27 31
S5 Multiexponential fit of the the local excited state dynamics
The convolution of a Gaussian function with the sum of three exponential functions was used to analyse the time profiles around the LES transient absorption band,ESALES. The width of the Gaussian (FWHM = 85 fs) was determined from the analysis of a Kerr e↵ect measurement at the same wavelength as theESALESand was then kept constant for all samples. The amplitude-averaged lifetime of the first two exponentials,h⌧i, was used to estimate the decay dynamics, whereas the third exponential accounted for the o↵set due to the absorption of the CSS. The TA profiles and the best fits are shown in Figure S3, whereas theh⌧ivalues are listed in Table S2.
Kerr Effect acetonitrile IVs IVa
IIIs IIIa
IIs IIa
Ia
Figure S3: Time profiles of the LES TA signal and best fits. The fit is a convolution of a Gaussian function with a full width at half maximum of 85 fs and the sum of three exponentials.
S6
8.1 Paper I - Supporting Information 95
S6 Position of the the charge-separated state (CSS) TA band
To better determine the peak position of the CSS band, the spectrum at each time step is analysed with a Gaussian function. At each time step, a spectral region around the band maximum, where the band can be reproduced with a Gaussian function, was defined. The best Gaussian was then obtained by a least-square fit of this spectral region as indicated in Figure S4A.
A B C
τ = 127 fs
τ = 630 fs
Figure S4: (A) Determination of the CSS band position using a Gaussian fit near the band maximum (solid line) of IVs. (B) Time dependence of the CSS band maximum ofIVsin methylcyclohexane (MCH) and acetonitrile (ACN) with the best exponential fits (dashed lines) (C) Residual from the exponential fit of the data in B illustrating the wavepacket motion.
S7
S7 Wavepacket analysis
In the following, we describe the two approaches used to determine the oscillation frequency of the vibrational wavepacket observed with dyadsIIs,IIIs,IVaandIVs. Both methods give the same result.
In the first approach, the TA data were analysed globally assuming a series of successive exponential steps. The resulting decay-associated di↵erence spectra (DADS) and evolution-associated di↵erence spectra (EADS) together with the time constants are illustrated in Figures S5 -S9. A subtraction of the best fit from the experimental data gives the residual matrix, which only contains the oscillations due to wavepacket motion. The nodes indicate the spectral position of the feature which oscillates. In the present case, the nodes are located at the maximum of two CSS bands. A Fourier transformation of the residual matrix gives a frequency spectrum at each probe wavelength.
In the second approach, the time dependence of the CSS band maximum is analysed with an exponential function, and the residual that contains only the oscillation is Fourier transformed. As indicated in Figures S5 -S9, both methods give the same result.
Figure S5: Wavepacket analysis of the TA data obtained withIIsin acetonitrile. Fourier transformation of the residual matrix obtained from global lifetime analysis and of the residuals obtained from the peak position gives the same result.
Figure S6: Wavepacket analysis of the TA data obtained withIIIsin acetonitrile. Fourier transformation of the residual matrix obtained from global lifetime analysis and of the residuals obtained from the peak position gives the same result.
S8
8.1 Paper I - Supporting Information 97
Figure S7: Wavepacket analysis of the TA data obtained withIVain acetonitrile. Fourier transformation of the residual matrix obtained from global lifetime analysis and of the residuals obtained from the peak position gives the same result.
Figure S8: Wavepacket analysis of the TA data obtained withIVsin acetonitrile. Fourier transformation of the residual matrix obtained from global lifetime analysis and of the residuals obtained from the peak position gives the same result.
S9
Figure S9: Wavepacket analysis of the TA data obtained withIVsin methylcyclohexane. Fourier transformation of the residual matrix obtained from global lifetime analysis and of the residuals obtained from the peak position gives the same result.
S10
8.1 Paper I - Supporting Information 99
S8 Assignment of the oscillation to a normal mode
The assignment of the frequencies obtained from the wavepacket analysis to normal modes in the dyads was based on quantum chemistry calculations. They were performed at the density functional theory (DFT) level. Ground-state calculations, namely geometry optimisation and frequency calculations, were carried out using the B3LYP functional and the 6-311++G(d,p) basis set. Among the few modes with a frequency in the 100-200 cm 1region, only one follows the experimentally observed dependence on the electron donor. This mode corresponds to an in-plane distortion of the NDI core and a stretching of the N-C bond between the NDI and the donor (Figure S10).
For the symmetric compounds, this vibration is symmetric and its anti-symmetric counterpart is above 200 cm 1.
Figure S10: Displacement vectors associated with the vibrational mode ofIVaat ¯⌫DA= 168 cm 1.
As shown in Figure S11 as well as in Table S3, the calculated and observed frequencies as well as their dependence on the donor match very well. The antisymmetric vibration is observed at 206 cm 1withIVs, which undergoes the fastest CS. ForIIsandIIIs, this vibration is predicted to be at higher frequency (⇠260 cm 1) and is not visible, probably because of the slower CS.
Figure S11: Comparison of the frequency of the symmetric ¯⌫DAmode obtained from the DFT calculations with the frequency obtained from the wavepacket analysis. Its absolute value as well as its dependence on the donor agree closely.
Table S3: Comparison of the frequencies of the symmetric and anti-symmetric ¯⌫DAmodes obtained from the DFT calculations with the frequencies obtained from the wavepacket analysis. All frequencies are given in cm 1.
Dyad Wavepacket analysis Calculated (symmetric) Calculated (antisymmetric)
IVs 142,206 137 206
IVa 170 168
-IIIs 150 160 261
IIs 168 176 263
S11
S9 Time-dependent density functional theory (TD-DFT) calculations S9.1 TD-DFT of IVa
TD-DFT calculations were carried out using the CAM-B3LYP functional together with the 6-31G(d,p) basis set.
Ground-state frequency calculations with this combination gave very similar frequencies as those obtained above with the more expensive 6-311++G(d,p) basis set. These calculations performed withIVaat the ground-state equilibrium geometry predict a S1 S0transition at 3.81 eV with an oscillator strength of 0.45. This transition has a⇡ ⇡⇤character and is fully localised on the NDI core (Figure S12 left). The S1state corresponds to the LES. The S2 S0is very close, at 3.8 eV, and its oscillator strength is close to zero (10 4). It is dominated by a one electron transition from the HOMO, localised on the mesitylene donor, to the LUMO, centred on the NDI core, pointing to a strong charge-transfer character (Figure S12 right). The S2state can thus be associated with the CSS. The negligibly small oscillator strength of the S2 S0transition indicates that this state is not photo-accessible from the ground state. These results confirm that the experimentally observed absorption band of the dyads is due to a transition to the LES and that the broadening cannot be ascribed to an overlapping charge-transfer transition.
S1 S0 S2 S0
Figure S12: Electron density di↵erence of the S1 S0and S2 S0transitions illustrating their local and charge-transfer character, respectively. A decrease of electron density is depicted in blue whereas and increase is shown in red.
S9.2 Geometry optimization of the S1and S2states
Figure S13 compares the energies of the S0state, LES and CSS ofIVain vacuum calculated at their equilibrium geometry. The calculations reveal that, after equilibration, the CSS is the lowest electronic excited state ofIVa.
As shown in Table S4,IVais weakly polar in the S0state and the LES with a permanent dipole moment,|~µp|, of about 0.5 D. However, the CSS is highly polar with|~µp|= 16 D. Figure S14 also points to much larger structural changes upon LES!CSS transition that upon LES S0 excitation. For example, the length of the N-C bond between the N imide atom and the donor C is essentially the same in the S0 state and the LES, but shrinks considerably upon charge separation.
Figure S13: Energy levels ofIVacalculated at the ground state (S0), locally-excited state (LES), and charge-separated state (CSS) equilibrium geometry.
S12
8.1 Paper I - Supporting Information 101
Figure S14: Bond lengths (in pm) obtained from geometry optimisation ofIVain the ground state (S0), the LES and the CSS.
Table S4: Parameters obtained from geometry optimisation ofIVain the ground (S0), the S1(LES), and the S2
states (CSS).
S0 LES CSS
NDI-D dihedral / deg 81.6 80.2 74
|~µp|/ D 0.52 0.54 16.0
¯
⌫DA/ cm 1 173 173 178
References
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[5] Lang, B.Rev. Sci. Instrum.2018,89, 093112.
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S13
S10 Appendix
Figure S15:1H NMR spectrum of compoundIIIain CDCl3(500 MHz).
Figure S16:13C NMR spectrum of compoundIIIain CDCl3(500 MHz).
S14
8.1 Paper I - Supporting Information 103
Figure S17:1H NMR spectrum of compoundIIIsin CDCl3(500 MHz).
Figure S18:13C NMR spectrum of compoundIIIsin CDCl3(500 MHz).
S15
Figure S19:1H NMR spectrum of compoundIVain CDCl3(500 MHz).
Figure S20:13C NMR spectrum of compoundIVain CDCl3(500 MHz).
S16
8.1 Paper I - Supporting Information 105
Long-lived triplet charge-separated state in naphthalenediimide based donor-acceptor systems.
Alexander Aster, Christopher Rumble, Anna-Bea Bornhof,
Hsin-Hua Huang, Naomi Sakai, Tom´aˇs ˇSolomek, Stefan Matile, and Eric Vauthey∗
Electronic Supplementary Information
Contents
S1 Synthesis . . . . S2 S2 Experimental Details, Spectroscopy . . . . S2 S2.1 Chemicals . . . . S2 S2.2 Absorption . . . . S2 S2.3 UV-Vis Transient Absorption . . . . S2 S2.3.1 General Remarks . . . . S2 S2.3.2 Visible Probe . . . . S2 S2.3.3 fs-ps Pump . . . . S2 S2.3.4 ps-µs Pump . . . . S2 S2.3.5 Data Treatment . . . . S2 S2.4 Mid-Infrared (IR) Transient Absorption . . . . S3 S3 Solvent dependence of the photophysics of pNDI . . . . S4 S4 Estimation of the triplet quantum yield of pNDI . . . . S5 S5 Steady-state electronic absorption spectra of I-V . . . . S6 S6 Electron-transfer dynamics of I-V in ACN . . . . S7 S7 Triplet sensitization experiments . . . . S8 S8 Transient absorption spectra measured with pNDI and I-IV in ACN . . . . S9 S9 Global lifetime analysis and evolution associated difference spectra . . . S10 S9.1 General . . . S10 S9.2 fs-ps Vis-TA ofpNDIin MCH . . . S10 S9.3 fs-ps Vis-TA ofpNDIin ACN . . . S11 S9.4 fs-ps Vis-TA ofpNDIin HFP . . . S11 S9.5 fs-ps Vis-TA ofIain ACN . . . S12 S9.6 fs-ps Vis-TA ofIIain ACN . . . S13 S9.7 fs-ps IR-TA ofIIain ACN . . . S13 S9.8 fs-ps Vis-TA ofIIsin ACN . . . S14 S9.9 fs-ps Vis-TA ofIIIain ACN . . . S15 S9.10 fs-ps IR-TA ofIIIain ACN . . . S15 S9.11 fs-ps Vis-TA ofIIIain MCH . . . S16 S9.12 fs-ps IR-TA ofIIIain MCH . . . S16 S9.13 fs-ps Vis-TA ofIIIain HFP . . . S17 S9.14 fs-ps Vis-TA ofIIIsin ACN . . . S18 S9.15 fs-ps Vis-TA ofIVain ACN . . . S19 S9.16 fs-ps IR-TA ofIVain ACN . . . S19 S9.17 fs-ps Vis-TA ofIVain MCH . . . S20 S9.18 fs-ps IR-TA ofIVain MCH . . . S20 S9.19 fs-ps Vis-TA ofIVsin ACN . . . S21 S9.20 fs-ps Vis-TA ofIVsin MCH . . . S22 S9.21 fs-ps Vis-TA ofVsin ACN . . . S23 S9.22 fs-ps Vis-TA ofVsin THF . . . S24 S9.23 fs-ps Vis-TA ofCagein THF . . . S25 S10 ns-µs Vis-TA of Cage and Vs in THF . . . S26
S1
S1 Synthesis
pNDI,1 Ia,2IIa,1 IIs,3IIIa,4 IIIs,4IVa,4IVs,3 Vs5 andCage6 are known compounds and their NMR spectra were in agreement with the literature.
S2 Experimental Details, Spectroscopy S2.1 Chemicals
Acetonitrile (ACN, Roth, ≥ 99.9%), methylcyclohexane (MHX, Roth,≥ 99%), hexafluoro-2-propanol, (HFP, Sigma-Aldrich,≥99%), tetrahydrofuran (THF, Roth≥99%) and n-buthylether (NBE,≥99%, Acros) were used as received.
S2.2 Absorption
Absorption spectra were measured on a Cary 50 spectrometer.
S2.3 UV-Vis Transient Absorption
S2.3.1 General Remarks
The visible transient absorption (TA) data presented in this work were recorded with a fs-ps visible (fs-VIS) and a ps-µs visible (ps-VIS) TA setups. A detailed description of the general principle of the fs-ps as well as ps-µs TA applying referenced detection with two spectrographs is presented elsewhere.7The designs of the fs-VIS and the
The visible transient absorption (TA) data presented in this work were recorded with a fs-ps visible (fs-VIS) and a ps-µs visible (ps-VIS) TA setups. A detailed description of the general principle of the fs-ps as well as ps-µs TA applying referenced detection with two spectrographs is presented elsewhere.7The designs of the fs-VIS and the