Electronic excitations in conjugated. Many-Body Green's Functions. Behnaz Bagheri Varnousfaderani. Behnaz Bagheri Varnousfaderani

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1 Technische Universiteit Eindhoven University of Technology Electronic excitations in conjugated polymers Electronic from excitations QM/MM simulations in conjugated pol based from on Many-Body QM/MM simulations Green's Functions based on Many-Body Green's Functions Behnaz Bagheri Varnousfaderani Behnaz Bagheri Varnousfaderani Department of Mathematics and Computer Science Centre for Analysis, Scientific Computing, and Applications Supervisors: Björn Baumeier, Mikko Karttunen Department of Mathematics and Computer Science, Centre for Analysis, Scientific Computing, and Applications W&I

2 Motivation Polymer Dots as Fluorescent Probes Changfeng Wu and Daniel T. Chiu, Angew. Chem. Int. Ed. 2013, 52,

3 Motivation Poly para phenylene ethynylenes (PPEs) Electronic degrees of freedom DFT Classical degrees of freedom Forcefield n=degree of polymerization Questions: DFT Classical MD Effect of Backbone Sidechain Solvent in conformation electronically GW-BSE QM/MM

4 Classical Molecular Dynamics... Number of atoms we are dealing with in this kind of simulations including polymer and solvent: around a million atoms Number of atoms that QM can handle : 300 QM Classical MD Bonded: covalent bond-stretching, angle-bending, improper dihedral, and proper dihedrals Nonbonded: Lennard-Jones or Buckingham, Coulomb or modified Coulomb Forcefield Parametrization

5 Check QM-MM Compatibility Optimization of PPE 5mer geometry, vacuum, T=0K: DFT, B3LYP, def2-tzvp, Orca: Co-planar configuration of phenyl rings along the backbone OPLS-type force field, as used in [Maskey et al, ACS Macro Lett. 2, , 2013, Maskey et al, J. Chem. Phys. 134, , 2011, Wijesinghe et al, Journal of Polymer Science, Part B: Polymer Physics, 54, , 2016], GROMACS: Alternating twisted arrangement of phenyl rings along the backbone Ground state potential energy surface differs in MM and QM descriptions! Potentially strong deviations in calculations of optical excitations.

6 Torsional Potential in DPE diphenylethyne (DPE) 4 modified FF B3LYP+D3 Energy (kj/mol) original FF 1 Energy 298K) Experiment: phenyl torsion (deg) co-planar conformations, barrier of ~2kJ/mol at 90 degrees [Halkyard et al, Macromolecules, Vol. 31, No. 25, 1998, Moore, J. S. in Modern Acetylene Chemistry, 1995] Addition of torsion potential to FF to fit QM PES!

7 DPE-CH3 Validation "trans"-dpe-ch3 Energy (kj /mol) modified FF B3LYP+D3 original FF "cis"-dpe-ch3 1 0 Energy 298K) phenyl torsion (deg) Modified FF seems reasonable. cis-trans preference driven by dispersion interactions among the side chains

8 Many-Body Green's Function Theory DFT Electronic ground state

9 DPE-CH3 optical properties Optical absorption profile of DPE-CH3 as a function of phenyl torsion DFT geometries MM geometries Good baseline established to investigate optical properties of PPE based on MM conformations.

10 DPE-CH3 optical properties DFT geometries MM geometries Good baseline established to investigate optical properties of PPE based on MM conformations.

11 PPE degree of polymerization=20 Energy minimized structure in vacuum at T=0 K, (steep, sd 30 K, steep): Energy minimized structure in vacuum at T=300 K, (sd, 1ns nvt simulation at T=300K with 1fs time step):

12 dinonyl PPE, degree of polymerization=20 Energy minimized structure in vacuum at T=0 K, (steep, sd 30 K, steep): Energy minimized structure in vacuum at T=300 K, (sd, 1ns nvt simulation at T=300K with 1fs time step):

13 Adding Explicit Solvent Toluene: Density: 0.87 g/ml (20 C) Water: Parametrized in OPLS Toluene good solvent for the backbone poor solvent for the side chain Using OPLS FF, SPCE Water is a poor solvent for both the backbone and sidechains

14 Adding Explicit Solvent 100ps NVT simulation followed by 4.2ns NPT at T=300K, 1fs time step: The nonyl side chains start aggregating toward the PPE backbone in agreement with [Maskey et al, ACS Macro Lett. 2, , 2013, Maskey et al, J. Chem. Phys. 134, , 2011, Wijesinghe et al, Journal of Polymer Scinece, Part B: Polymer Physics, 54, , 2016]

15 Expilicit Toluene Solvent 100ps NVT simulation followed by 5.2ns NPT at T=300K, 1fs time step: The backbone of PPE remains extended as was experimentally observed by SANS [Perahia et al, Macromolecules 34, 151, 2001]. The side chains are dispersed and separated from each other as well as away from the backbone in agreement with [Maskey et al, ACS Macro Lett. 2, , 2013, Maskey et al, J. Chem. Phys. 134, , 2011, Wijesinghe et al, Journal of Polymer Scinece, Part B: Polymer Physics, 54, , 2016]

16 Order Parameter 1 dinonyl PPE, degree of polymerization mers-Toluene 20mers-Water < Pθ > PPE without side chain degree of polymeization 20 < Pθ > n mers-Toluene 20mers-Water n

17 dinonyl PPE degree of polymerization=10 100ps NVT simulation followed by 5.7ns NPT at T=300K, 1fs time step: mers-Toluene 0.6 < Pθ > n

18 Technische Universiteit Eindhoven University of Technology Outlook: Look at different samplings that we have different time series different side chains the efects of the polarization Water simulation

19 Technische Universiteit Eindhoven University of Technology Acknowledgement Sidath Wijesinghe, Dept Of Chemistry, Clemson University Electronic excitations in conjugated pol from QM/MM simulations based on Many-Body Green's Functions Behnaz Bagheri Varnousfaderani Department of Mathematics and Computer Science, Centre for Analysis, Scientific Computing, and Applications W&I