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Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes
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Origin of the Size-Dependent Fluorescence Blueshift in [n]Cycloparaphenylenes

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We present quantum chemical electronic structure calculations to investigate the nature of the low-lying excited states of [n]cycloparaphenylenes ([n]CPPs) and the role of static and dynamic …

We present quantum chemical electronic structure calculations to investigate the nature of the low-lying excited states of [n]cycloparaphenylenes ([n]CPPs) and the role of static and dynamic geometrical distortions in the bright states. The lowest-energy bright states involve single-electron excitations from S0 ground state to S2 and S3 states, which are at the Franck-Condon geometry the two components of a twofold degenerate 1E state. They couple to a twofold degenerate e vibration which induces Jahn-Teller (JT) deformation of the CPP geometry from circular to oval shape. Non-radiative decay from the S2/S3 states to the ground S0 and first excited, dark S1 states is suppressed due to symmetry rules. The emission spectral features in CPPs with large number of phenylene units n can therefore largely be attributed to the E ⊗ e JT system associated with S2 and S3. However, absorption and emission energies computed at the respective S0 and S2/S3 minimum energy geometries are found to be nearly identical, independent of the molecular size n in the CPP molecules. In contrast, molecular dynamics simulations performed on the excited state potential surfaces are able to explain the experimentally observed fluorescence blueshift of the strongest emission peaks with increasing molecular size. This unusual feature turns out to be a consequence of large vibrational amplitudes in small [n]CPPs, causing greater Stokes shifts, while large [n]CPPs are more rigid and therefore feature smaller Stokes shifts (“dynamic blueshift”). For the same reasons, symmetry rules are violated to a greater extent in small [n]CPPs, and it is expected that in their case a “static blueshift” due to emission from S1 contributes in the fluorescence spectra.

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  • 1. 1Nagoya University http://qc.chem.nagoya-u.ac.jp 1 2Universität Regensburg PACCON 2013 Bangsaen Beach, Chon Buri, Thailand January 24, 2013 Origin of theSize-Dependent Fluorescence Blueshift in [n]Cycloparaphenylene Stephan Irle,1Cristopher Camacho,1 Thomas Niehaus,2Kenichiro Itami1 2Electron Dynamics in Complex Systems Group, Universität Regensburg 1Quantum Chemistry of Complex Systems, Nagoya University
  • 2. 2 [n]Cycloparaphenylenes (Collaboration with Itami Group) We have a dream: Omachi, Matsuura, Segawa, Itami, Angew. Chem. Int. Ed. 49, 10202 (2011) Prof. Itami
  • 3. Ground state PES 3Segawa, Omachi, Itami, Org. Lett. 12, 2262 (2010) (Supporting Material) Linear relationship between strain energy and size n q Similar to carbon nanotubes! cf. Kudinet al., Phys. Rev. B61, 235406 (2001)
  • 4. Absorption and Emission Spectra 4Iwamoto, Watanabe, Sakomoto, Suzuki, Yamago, JACS 133, 8354 (2011) Blueshift in emission with increasing n!
  • 5. Absorption and Emission Spectra 5 “Nomal” redshift in open-polyparaphenylenes TD-CAM-B3LYP/SV(P)
  • 6. Biphenyl p-MOs 6 Constant amplitude, a+2b Constant amplitudes, a-2b 2b a HOMO = - LUMO = + p-bond!
  • 7. CPP frontier MO’s • MO level diagram n=12, D6d symmetry: • HOMO-LUMO excitation is symmetry-forbidden! • e MOs behave like x and y functions • LUMO+1HOMO and LUMOHOMO-1 excited states are both of E1 symmetry, they mix! • 4 states: e1 a2 a1 e1 LUMO+1 LUMO HOMO HOMO-1 x y HOMO-2 LUMO+2 nodal plane (LUMO+1xHOMO)+(LUMOHOMO-1x) (LUMO+1yHOMO)+(LUMOHOMO-1y) (LUMO+1xHOMO)-(LUMOHOMO-1x) (LUMO+1yHOMO)-(LUMOHOMO-1y) 1E1 2E1 7 e Bright! Dark!
  • 8. [n]CPP frontier MO’s 8 CAM-B3LYP/SV(P) at ground state optimized structures (all alternating conformations) No Blue-shift inbright transitions! HOMO-LUMO gap increasing with increasing n!
  • 9. 9 [n]cPP: [2n]cPP cut in half, fixed geometry [n]CPP frontier MO’s [n]OPP: [2n]cPP cut in half but linear, optzd. HOMO-LUMO gap in [3]OPP Stronger p-antibonding Stronger p-bonding in [n]CPP [∞] OPP HOMO CAM-B3LYP/SV(P) @ S0opt’d geometries [∞] OPP LUMO
  • 10. 10 Energy [eV] 1A1 21E1 11E1 1A’1A’ Qq 2 1Bx -Qq 1 1Bx 3 1By 4 1By 2 1By 1 1By 3 1Bx 4 1Bx Qq = x2-y2 -Qq= -(x2-y2) Jahn Teller Energy Diagram (schematic)
  • 11. 11 Jahn Teller DistortionCoordinates Qe&Qq nodal plane -Qq = -x2+y2Qe = xy [10]CPP
  • 12. Absorption and Emission Spectra 12 1E1 Emission: at least 2 intensive peaks!
  • 13. Absorption and Emission Spectra 13 1E1 Absorption: 1 peak Emission: at least 2 peaks!
  • 14. S0 S0 ’ S1 S1 ’ S0, S0’: ground state S1, S1’: lowest excited singlet state energy/hartree coordinate Energy diagramMethod  TURBOMOLE, GAMESS, DALTON  B3LYP/SV(P) level  sequence of calculations 1. optimization in the ground state 2. TD-DFT calculation at S0 structure 3. optimization in the excited state TD-DFT calculation at S1’ structure 1 2 absorption 3 fluorescence TD-DFT Methods 14 Geometry optimization in excited state
  • 15. Ground state geometries 15Segawa, Omachi, Itami, Org. Lett. 12, 2262 (2010) 2 local conformers: Many conformational isomers … [12]CPP [12]CPP [12]CPP [kcal/mol] B3LYP/6-31G(d)
  • 16. Ground state PES 16Segawa, Omachi, Itami, Org. Lett. 12, 2262 (2010) Ground state transition states for phenyl group rotation around f [12]CPP B3LYP/6-31G(d) f f
  • 17. [n]CPP UV/Vis spectra 17 Absorption: red Emission: red
  • 18. 18 [n]CPP UV/Vis spectra Absorption: artificially constant Emission: still red
  • 19. 19 [n]CPP UV/Vis spectra Absorption: ~constant Emission: ~constant
  • 20. 20 [n]CPP UV/Vis spectra Absorption: ~constant Emission: ~constant
  • 21. 21 [n]CPP UV/Vis spectra 1E1 Absorption: ~constant Emission: ~constant
  • 22. Alternative to DFT: Approximate DFT Density-Functional Tight-Binding: Method using atomic parameters from DFT (PBE, GGA-type), diatomic repulsive potentials from B3LYP •Seifert, Eschrig (1980-86): minimum STO-LCAO; 2-center approximation •Porezag, Frauenheim, et al. (1995): efficient parameterization scheme: NCC- DFTB •Elstneret al. (1998): charge self-consistency: SCC-DFTB •Köhleret al. (2001): spin-polarized DFTB: SDFTB Marcus Elstner ChristofKöhler Helmut Eschrig Gotthard Seifert Thomas Frauenheim 22 MD in excited state Thomas Niehaus Linear response: TD-DFTB
  • 23. 23 CAM-B3LYPTD-DFTB/MD Electron Dynamics in Complex Systems Group, Universität Regensburg Linear response TD-DFTB: Thomas Niehaus Method  TD-DFTB w/mio-1-1 parameters  8 states considered, dynamics performed for S0, S1, S2/S3  MD: 1. starting from optimized geometries 2. NVT 0.5 ps equilibration at 298 K 3. NVE for 4.7 ps, production runs 4. CAM-B3LYP/SV(P) single point excited state calculations (up to 32 sample points)
  • 24. 24 Simulated [n]CPP UV/Vis spectra CAM-B3LYP/SV(P)TD- DFTB-MD snapshots Energy Energy Yes blueshift! Yes blueshift! Yes blueshift!
  • 25. 25 PESs during excited state dynamics f-fdihedral angle S2 S1 S0 S2-S0 S1-S0 S2 S1 S0 S2-S0 S1-S0 State energies during MD CAM-B3LYP/SV(P)TD-DFTB-MD Transition energies during MD
  • 26. 26 PESs during excited state dynamics State energies during MD Transition energies during MD CAM-B3LYP/SV(P)TD-DFTB-MD
  • 27. 27 Why Emission from S2? Energy difference between S1 and S2 very small, around 1 eV or smaller. Higher population of S2 than in usual organic molecules. Vibronic coupling matrix elements between S2 (u-type symmetry) and S0/S1 (g-type symmetry) since low energy molecular vibrations of circles behave as x2, y2 (g-type) radiationless decay from S2 “blocked” Consequence: -Emission from S2 easily possible in case of large n, while small CPP with ndistort also in x,y and emission becomes possible from S1. -Red shift for small n> red shift for large n  appearance of “blue shift” with increasing size n Published in: C. Camacho, Th. Niehaus, K. Itami, SI, Chem. Sci. 4, 187 (2013) ggu
  • 28. Absorption and Emission Spectra Explained 28 Absorption: 1 peak Dynamic blue- shift, emission from S2/S3 Static blue-shift, emission from S1
  • 29. Prof. Dr. Stephan Irle sirle@chem.nagoya-u.ac.jp Assist. Prof. Dr. Daisuke Yokogawa d.yokogawa@chem.nagoya-u.ac.jp WPI-Institute of Transformative Bio-Molecules & Department of Chemistry, Nagoya University of Complex Systems November 5, 2012 Back row: Yoshifumi Nishimura (D3), KosukeUsui (M2), Jun Kato (B4), Tim Kowalczyk (JSPS, PhD,), Cristopher Camacho-Leandro (PhD), Yoshio Nishimoto (JSPS, D1) Front row: Takayo Noguchi (secty), Naoto Baba (B4), Matt Addicoat (JSPS, PhD), SI, Arifin (G30, D1), Daisuke Yokogawa (Assist. Prof.)
  • 30. OUR GOAL is to develop “transformative bio-molecules”, innovative functional molecules that make a marked change in the form and nature of biological science and technology. Institute of Transformative Bio- Molecules (Nagoya University) EXPECTED OUTCOME Our ten-year campaign will culminate in a wealth of synthetic bio-molecules that will be key to solving urgent problems at the interface of chemistry and biology. The innovation in food/biomass production, optical technologies, and generation of new bio-energy can be imagined as our dream. THE IDENTITYof the Center is its capability to synthesize completely new bio-functional molecules with carefully designed functions. OUR UNIQUE APPROACH is to apply our cutting-edge synthesis (molecule-activation chemistry), with the support of computational chemistry, to synthesize key molecules to explore advanced systems biology in plants and animals.
  • 31. Several Postdoc positions open at the WPI! 2 positions in my group, specialty: biofluorescence, binding free energies (advertized on CCL.net) Institute of Transformative Bio- Molecules (Nagoya University)
  • 32. 33 Promotion http://admissions.g30.nagoya-u.ac.jp Undergraduate and Graduate Courses in Physics, Chemistry, and Biology in ENGLISH! Admissions for 2013 are currently ongoing. Nagoya University Toyota Auditorium JR Towers Nagoya Castle
  • 33. Thank you for your attention! 34

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