| 231. |
- Lin, Lili, et al.
(författare)
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Theoretical insights into the charge transport in perylene diimides based n-type organic semiconductors
- 2012
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Ingår i: Organic electronics. - : Elsevier BV. - 1566-1199 .- 1878-5530. ; 13:11, s. 2763-2772
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Tidskriftsartikel (refereegranskat)abstract
- We employed a tunneling enabled hopping model to investigate the charge transport properties for four n-type organic semiconductors perylene diimides compounds. The molecular parameters are calculated by density functional theory and the transport is modeled by kinetic Monte Carlo simulation. It is found that the substitutions at the bay positions of the perylene core have large influences on the charge transport properties through modifications in molecular conformation, the charge reorganization energy as well as the stacking networks in the crystals. The temperature dependence of the mobility shows typical "band-like", in agreement with the recent experiment, but we ascribe it to be the characteristic of nuclear tunneling effect for a localized charge, not by a delocalized band. The largest charge mobility is calculated to be 16.96 cm(2)/V s for the cyano substitution, in good comparison with the experimental value of 6 cm(2)/V s.
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| 232. |
- Lin, Lili
(författare)
-
Theoretical Modeling of Intra- and Inter-molecular Charge Transport
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on theoretical study of charge transportproperties in molecular systems. The understanding of the transportprocess and mechanism in molecular systems is essential forthe design of new functional molecular materials and molecularelectronic devices. The molecular junctions and organic molecularcrystals have been used as the model systems to highlight the usefulnessof theoretical modelling. A molecular junction is a system that consists ofone or several molecules sandwiched between two electrodes.The charge transport in molecular junctions is a very complex processthat is affected by the interaction between molecules and electrodes,the surroundings, as well as electron-electron (e-e) andelectron-phonon (e-p) couplings. When the molecule-electrode couplingis strong, the transport process can be very quick. If the e-p couplingis weak, the inelastic tunneling has only negligible contributions to thetotal current and the elastic electron tunneling plays the dominant role.Furthermore, the hopping process becomes dominant in the case of strong e-pcoupling, for which the geometric relaxation of the molecule needsto be considered. In this thesis, we have examined these three kinds oftransport processes separately. The first studied system is a molecular junction consisting of aromaticallycoupled bimolecules. Its elastic electron tunneling property is simulatedusing Green's functional theory at density functional theory level.The dependence of the conductance of bimolecular junctions on the vertical distances,horizontal distances and the tilt angles has been systematically studied. Theinelastic electron tunneling spectra (IETS) of molecular junctions have beencalculated for several systems that were experimentally measured with conflictingresults and controversial assignments. Our calculations provide the reliableassignments for the experimental spectra and revealed unprecedented detailsabout the molecular conformations within the junctions under different conditions.It demonstrates that a combined theoretical and experimental IETS study is capableof accurately determining the structure of a single molecule inside the junction.The hopping process is a dominant charge transfer process in organic molecularcrystals. We have studied the charge transport ability of four kinds of n-typeorganic semiconductor materials to find out the related structure-to-propertyrelationship. It is done by adopting the quantum charge transfer rate equationcombined with the random walk approach.
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| 233. |
- Lin, Na, et al.
(författare)
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Differences in Two-Photon and One-Photon Absorption Profiles Induced by Vibronic Coupling : The Case of Dioxaborine Heterocyclic Dye
- 2011
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Ingår i: ChemPhysChem. - : Wiley. - 1439-4235 .- 1439-7641. ; 12:17, s. 3392-3403
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical study of a dioxaborine heterocyclic compound in solution provides a case study for an analysis of the effects induced by the so-called HerzbergTeller (HT) vibronic coupling on the one- (OPA) and two-photon absorption (TPA) spectra. For TPA, the HT vibronic coupling induces differences in the shapes of the absorption band. The study highlights the importance of vibronic coupling as a potentially important mechanism in absorption spectroscopy, able to explain differences in the OPA/TPA spectra.
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| 234. |
- Lin, Na, et al.
(författare)
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Solvent Effects on the Three-Photon Absorption of a Symmetric Charge-Transfer Molecule
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112, s. 4703-4710
-
Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical study of the solvent-induced three-photon absorption cross section of a highly conjugated fluorene derivative, performed using density functional (DFT) cubic response theory in combination with the polarizable continuum model. The applicability of the often used two-state model is examined by comparison against the full DFT response theory results. It is found that the simplified model performs poorly for the three-photon absorption properties of our symmetric charge-transfer molecule. The dielectric medium enhances the three-photon absorption cross section remarkably. The effects of solvent polarity and geometrical distortions have been carefully examined. A detailed comparison with experiment is presented.
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| 235. |
- Lin, Na, 1981-
(författare)
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Theoretical Studies on Electronic and Vibrationally Resolved Multi-Photon Absorption and Dichroism
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents time-dependent density functional theory studies on electronic and vibronically resolved linear and nonlinear optical absorption and dichroism spectra of organic molecules. Special attention has been paid to the influence of solvent environment and molecular vibrations on one-, two- and three-photon absorption and one- and two-photon circular dichroism. It is found that dielectric medium as described by polarizable continuum model can enhance remarkably three-photon absorption cross section of a highly conjugated fluorene derivative, for which the simplified two-state model is shown to be largely inadequate. Origin-invariant density functional calculations on one- and two-photon circular dichroisms of a chiral molecule confirm that the recently developed CAMB3LYP functional performs better than the popular B3LYP functional for Rydberg-states. The first experimental measurement of TPCD spectra is performed on an axial chiral system in tetrahydrofunan, where the double L-scan technique is applied. Theoretical calculations well reproduce the experimental profiles when both the electron correlation and the solvent effect are taken into account. Vibronically resolved one- and two-photon absorption spectra of charge-transfer molecules have been obtained using a Linear Coupling model, where the 'borrowing mechanism' for the so-called Herzberg-Teller contribution is analyzed in detail. It is shown that Herzberg-Teller contribution can introduce a change of sign to the chiral responses of a molecule without the involvement of different electronic states, which has important consequences for the assignment of absolute configurations of chiral molecules. Adiabatic harmonic Franck-Condon model is also applied to simulate vibronically resolved one- and two-photon circular dichroism spectra of the same chiral system, where the sign-inversion and the interference between Franck-Condon and Herzberg-Teller contributions are also observed.
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| 236. |
- Lin, Na, et al.
(författare)
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Theory for Vibrationally Resolved Two-Photon Circular Dichroism Spectra : Application to(R)-(R)-(R)-(+)-3-Methylcyclopentanone
- 2009
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 113:16, s. 4198-4207
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Tidskriftsartikel (refereegranskat)abstract
- A harmonic adiabatic approach in combination with density functional response theory for computing twophotonvibronically resolved circular dichroism spectra of chiral molecules is presented. It includes bothFranck-Condon and Herzberg-Teller contributions and it takes fully into account frequency changes andDuschinsky effects. Model calculations have been performed for two dominant conformers of (R)-(+)-3-methylcyclopentanone in the gas phase. It is found that the Herzberg-Teller contribution can introduce asign change in two-photon circular dichroism of a single excited electronic state of a conformer. The changesurvives after Boltzmann averaging, and it might be amenable to experimental verification. Interestinginterference effects between Franck-Condon and Herzberg-Teller contributions are revealed and analyzedin detail. Results obtained within the more approximate and less computationally intensive linear couplingvibronic model are also given for comparison.
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| 237. |
- Lin, Na, et al.
(författare)
-
Vibronic induced one- and two-photon absorption in a charge-transfer stilbene derivate
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:244509
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Tidskriftsartikel (refereegranskat)abstract
- Both the electronic and the vibronic contributions to one- and two-photon absorption of a D-pi-D charge-transfer molecule (4-dimethylamino-4(')-methyl-trans stilbene) are studied by means of density functional response theory combined with a linear coupling model. Vibronic profiles of the first four excited states are fully explored. The dominating vibrational modes for both Franck-Condon and Herzberg-Teller contributions are identified. The Franck-Condon contribution dominates the spectra of first, second, and fourth excited states. The Herzberg-Teller contribution is on the other hand of comparable size for the third excited state, where its inclusion leads to a blueshift with respect to the vertical transition. A similar vibronic coupling behavior is found for both one- and two-photon absorptions
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| 238. |
- Lin, Na, et al.
(författare)
-
Vibronically-induced change in the chiral response of molecules revealed by electronic circular dichroism spectroscopy
- 2008
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 464, s. 144-149
-
Tidskriftsartikel (refereegranskat)abstract
- A computational study of the vibronically resolved electronic circular dichroism (ECD) spectra of R-(+)- 3-methyl-cyclopentanone, including both Franck-Condon and Herzberg-Teller contributions, shows how the latter can introduce a change of sign on the chiral response of an electronic excited state. This sign inversion within the vibronically resolved electronic band, which can be interpreted as a change of the chirality of the system, has in principle important consequences in comparisons of theoretical and experimental ECD spectra employed for the assignment of absolute configurations.
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| 239. |
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| 240. |
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