Article
Reference
The Origin of the Solvatochromism in Organic Fluorophores with Flexible Side Chains: A Case Study of Flugi-2
WOLFF, Franziska E., et al.
Abstract
The emission band for Flugi-2 solvated in dimethyl sulfoxide (DMSO) is obtained from the combined quantum–classical simulations in which the quantum mechanics/molecular mechanics excitation energies are evaluated at the equilibrated segment of the classical molecular dynamics trajectory on the lowest-excited-state potential energy surface. The classical force-field parameters were obtained and validated specifically for the purpose of the present work. The calculated gas-phase to DMSO solvatochromic shift amounts to −0.21 eV, which is in line with the experimentally determined difference between the maxima of the emission bands for Flugi-2 in decane and in DMSO (−0.26 eV). The used model describes rather well the effect of DMSO on the broadening of the emission band. The solvatochromic shift in DMSO originates from two competing effects. The structural deformation of Flugi-2 due to the interaction with DMSO, which results in a positive contribution, and the negative contribution of a larger magnitude due to favorable specific interactions with the solvent. The latter is dominated by a single hydrogen bond between [...]
WOLFF, Franziska E.,
et al. The Origin of the Solvatochromism in Organic Fluorophores with Flexible Side Chains: A Case Study of Flugi-2.
Journal of Physical Chemistry. A, 2019, vol.
123, no. 21, p. 4581-4587
DOI : 10.1021/acs.jpca.9b02474
Available at:
http://archive-ouverte.unige.ch/unige:144564
Disclaimer: layout of this document may differ from the published version.
The Origin of the Solvatochromism in Organic
Fluorophores with Flexible Side Chains: A Case Study of Flugi-2
Supporting Information
Franziska E. Wolff1, Sebastian Höfener2, Marcus Elstner3, and Tomasz A.
Wesolowski4
1Department of Theoretical Chemical Biology, Institute of Physical Chemistry, Karlsruhe Institute of Technology, Kaiserstrasse 12, 76131 Karlsruhe, Germany
2Department of Theoretical Chemistry, Institute of Physical Chemistry, Karlsruhe Institute of Technology, Kaiserstrasse 12, 76131 Karlsruhe, Germany
3Department of Theoretical Chemical Biology, Institute of Physical Chemistry and Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology,
Kaiserstrasse 12, 76131 Karlsruhe, Germany
4Université de Genève, Département de Chimie Physique, 30 quai Ernest-Ansermet, CH-1211 Genève 4, Switzerland
1 Additional results obtained various methods for geometry optimisation at ground- and excited states
The DFT optimisations, the calculation of the excitation energies and SORCI (Spectroscopy-Oriented multireference Configuration Interaction) calculations were carried out using the Orca program package and the split-valence basis set def2-SV(P).
For the SORCI calculations, a complete active space (CAS) with 12 electrons in 12 orbitals was used.
The geometry of the Flugi-2 molecule was optimised in the ground- and excited states using the range-separated (RS) functional WB97X as implemented in the Gaussian 09 in combination with the 6-31G* basis set.
For calculations including the conductor-like screening model (COSMO), the dielectric constantεwas set to 47.8.
InTable S1, excitation energies and Stokes shifts for Flugi-2 are collected at different levels of theory. Concerning the excitation energies of the CC2 gas phase geometries,
It is not the case for SORCI calculations, which is able to reproduce the Stokes shift, but the transition energies are shifted by 0.2 eV compared to experiment.
Similarly, range-separated DFT using the functional WB97X reproduces the Stokes shift, while the absolute values are shifted by 0.5 eV with respect to the experimental results.
The semiempirical method OM2 and DFTB are also able to reproduce the Stokes shift, while the absolute values of OM2 and DFTB are shifted by about 0.2 to 0.3 eV.
This deviation increases if range-separated functionals are used in DFTB (denoted RS-DFTB) calculations - the transition energies are shifted by about 0.5 eV from the experimental values.
To summarise, the CC2 geometries can be considered sufficiently accurate and the semi-empirical method OM2 is reliable to calculate qualitatively absorption and fluorescence energies of the molecular dynamics (MD) trajectories.
Table S1: Absorption and fluorescence energies of Flugi-2 obtained using various methods.
Geometries were optimised using WB97X/6-31G* and CC2/def2-TZVP.
excitation energy [eV] (oscillator strength) optimisation
method
method for excitation energy
Optimised at So
Optimised at S1
Stokes shift
CC2
CC2 3.22 (0.478) 2.56 (0.361) 0.66
WB97X 3.88 (0.535) 3.22 (0.416) 0.66 SORCI root3 3.04 (0.521) 2.36 (0.366) 0.68 SORCI root5 3.08 (0.588) 2.37 (0.411) 0.71
CIS 4.17 (0.307) 3.56 (0.537) 0.61
RS-DFTB 3.56 (0.714) 2.72 (0.666) 0.84
DFTB 2.80 (0.327) 2.19 (0.216) 0.61
OM2 3.57 (0.307) 2.88 (0.248) 0.69
Experiment (in Decane)
3.26 2.61 0.65
WB97X WB97X 4.17 (0.466) 3.35 (0.460) 0.82
SORCI root5 3.08 (0.3247) 2.50 (0.4659) 0.58
B3LYP B3LYP 3.29 (0.459) - -
WB97X 4.003 (0.4971) - -
Table S2: Fluorescence emission energies at the excited state geometries obtained using several methods. The geometries are optimised using either CC2 or DFT/ωB97X methods, for both isolated and solvated Flugi-2. The solvent (DMSO) was represented using either implicit model (COSMO) or as one DMSO molecule bonded to the N3-H atom.
Excitation Method
Optimization
Method CC2 ωB97X ωB97X ωB97X
gas phase gas phase solvent solvent COSMO one DMSO molecule
CC2 gas phase 2.56 - - -
SORCI gas phase 2.37 2.50 2.43 -
SORCI solvent 2.35 2.50 2.44 -
DFT/ωB97X gas phase 3.22 3.35 3.31 3.17
DFT/ωB97X solvent 3.05 3.20 3.14 3.07
OM2/MRCI gas phase 2.88 3.01 2.94 2.88
OM2/MRCI solvent 2.87 2.97 2.81 2.87
Table S3: Bond lengths (d) and the C8-C10 dihedral angles (θ) for the CC2 optimised geometries in the ground- and excited states. ”SB” and ”DB” indicate single and double bonds, respectively.
Bonds which change length by more than 0.02 Å are marked in red.
d S0 [Å] S1 [Å] |dS1−dSo|
C1=C2 1.37 1.39 0.02
C2-N1 1.37 1.38 0.01
N1-C3 1.42 SB 1.38 DB 0.04
C3-C5 1.39 DB 1.42 SB 0.03
C5=C4 1.39 DB 1.43 SB 0.04
C4-C1 1.42 1.40 0.02
C3=N2 1.34 1.36 0.02
N2-C8 1.37 1.36 0.01
C8=C9 1.41 1.42 0.01
C9-N1 1.37 DB 1.42 SB 0.05
C8-C10 1.46 1.44 0.02
C10-C11 1.41 1.41 0
C11=C12 1.39 1.39 0
C12-C13 1.40 1.40 0
C13=C15 1.40 1.40 0
C15-C14 1.39 1.39 0
C14=C10 1.40 1.41 0.01
C4-C6 1.48 1.46 0.02
C13-O3 1.36 1.36 0
C9-N3 1.39 SB 1.35 DB 0.04
θ S0 [◦] S1 [◦]
N2-C8-C10=C14 -18.70 -25.62 6.92
C9-N3-C16-C17 -59.09 -89.68 30.59
Table S4: Average lengths (single SB and double DB) and bond-alternation parameter (dBLA) for the CC2 optimised structures in ground- and excited states. The averages were calculated for the bonds with a strong bond inversion character in the excited state (marked in red inTable S3).
Ground state Excited state average DB [Å] 1.386 1.423 average SB [Å] 1.405 1.364
BLA 0.019 -0.059
2 Force-field parameters
2.1 Bonds
Table S5: Excited-state force-field parameters for heavy atom bonds.
bond force constant [kJ/nm2/mol] b0 [Å]
C1=C2 400325 1,3758
C4-C1 386434 1,3629
C2-N1 356477 1,3709
N1-C3 361163 1,3900
C9-N1 319490 1,4385
C3-C5 352209 1,4172
C3=N2 375723 1,3563
C5=C4 344511 1,3986
C4-C6 315808 1,4456
C6-O1 510448 1,2293
C6-O2 323088 1,3394
O2-C7 252295 1,4200
N2-C8 375723 1,3482
C8=C9 352209 1,3854
C8-C10 338151 1,4322
C9-N3 393547 1,3289
C10-C11 352209 1,4426
C14=C10 376476 1,4262
C11=C12 400325 1,4173
C12-C13 376476 1,4477
C13=C15 376476 1,4464
C13-O3 323088 1,3400
C15-C14 386434 1,4247
2.2 Dihedral angle C8-C10
Figure S1: CC2 and MM energies along the dihedral angle N2-C8-C10-C14: a) CC2 ground state (orange), b) CC2 excited state (black), c) MM ground state (blue), and d) MM excited state (red).
Table S6: C8-C10 dihedral angle parameter excited state.
dihedral parameter excited state
phi0 cp mult
N2-C8-C10-C11 180.000 6.245 2
N2-C8-C10-C14 180.000 6.245 2
C9-C8-C10-C11 180.000 0.965 2
C9-C8-C10-C14 180.000 0.965 2
2.3 Atomic charges
Table S7: Fitted charges of non-hydrogen atoms for the ground- and the excited state of Flugi-2 for the used force-field.
atom Ground state (HF) Excited state (DFT) difference excited state with COSMO (DFT)
C1 -0,193 -0,006 -0,187 -0,117
C2 -0,180 -0,440 0,260 -0,310
N1 0,059 0,150 -0,092 -0,064
C3 0,469 0,564 -0,095 0,791
C4 -0,162 -0,545 0,384 -0,438
C5 -0,261 -0,384 0,122 -0,575
C6 0,863 1,063 -0,200 1,059
O1 -0,598 -0,645 0,047 -0,736
O2 -0,418 -0,318 -0,100 -0,339
C7 -0,034 -0,258 0,224 -0,269
N2 -0,624 -0,669 0,045 -0,838
C8 0,149 0,150 -0,002 0,087
C9 0,175 0,674 -0,499 0,879
N3 -0,850 -1,235 0,385 -1,328
C10 0,000 -0,797 0,797 -0,662
C11 -0,061 0,616 -0,677 0,443
C12 -0,398 -1,311 0,913 -1,244
C13 0,503 1,248 -0,745 1,254
C14 -0,061 0,941 -1,002 0,828
C15 -0,398 -1,100 0,702 -1,111
C16 0,430 0,107 0,323 0,199
H11 0,386 0,515 -0,129 0,563
C17 -0,083 1,131 -1,214 1,223
C18 -0,083 0,685 -0,769 0,773
C19 -0,033 -0,502 0,469 -0,478
C20 -0,014 0,754 -0,767 0,787
C21 -0,033 -0,637 0,604 -0,633
O3 -0,411 -0,290 -0,121 -0,343
C22 0,078 -0,620 0,698 -0,612
3 Excited state of Flugi-2
Figure S2: The pair of orbitals providing the dominant contribution (86%) to the lowest excited state for isolated Flugi-2: HOMO (top) and LUMO (bottom)
4 Excited-state MD simulations
Figure S3: Simulated emission spectra of isolated and solvated Flugi-2.
Figure S4: Oscillator strengths and excitation energies used for the histogram shown in Figure S5.
Figure S5: Intensity weighted histograms of S0-S1 OM2 energy differences for solvated Flugi-2 along two MD trajectories onS1surface: (blue) trajectory obtained using gas phase charges and (green) trajectory obtained using for COSMO charges.
