Theoretical investigation of the structure and the electron-vibrational dynamics of 9,9′-spirobifluorene (original) (raw)
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The linear absorption and fluorescence spectra as well as the oscillator strengths of 2,2¢,7,7¢-tetraphenyl- 9,9¢-spirobifluorene (A), 2,2¢,7,7¢-tetrakis(biphenyl-4-yl)-9,9¢-spirobifluorene (B), and 2,2¢,7,7¢-tetrakis(9,9¢- spirobifluoren-2-yl)-9,9¢-spirobifluorene (C) are calculated on the basis of the collective electronic oscillator (CEO) approach of Mukamel et al. (see, e.g., Chem. ReV. 2002, 102, 3171). The graphical visualization and quantitative characterization of CEO modes allows one to extract the real-space distribution of electronic excitations of the molecules under study. Effects of the lengthening and branching of the oligophenylene segments have been analyzed. The influence of the lowest excited (S1) vs ground-state (S0) geometry changes on the CEO modes is investigated and related to the geometry changes of the molecular parts. The obtained theoretical results are in good agreement with experimental trends observed in absorption and fluorescence data.
Ab initio, DFT, and spectroscopic studies of excited-state structure and dynamics of 9-ethylfluorene
Journal of Molecular Structure, 2008
Fluorescence excitation and resonant two-photon ionization spectra were measured for 9-ethylfluorene (EFR) molecule cooled in pulsed supersonic expansion of He in the range of 286.5 $ 300 nm. The structures and energies of the global and local minima and the transition states separating them are evaluated with the B3LYP/6-31G(d) and MP2/cc-pVTZ methods. It is found that the vertical excitation energies of fluorene and the EFR conformers can be reliably predicted by the time-dependent DFT method within 8.72%. The vibrational bands above the electronic origin are assigned on the basis of the RCIS/6-31G(d) calculation. Ethyl (or ethene) elimination from the excited neutral and/or ionic molecule is presumed to occur as an activation process along the adiabatic potential energy surface.
On electronic structure of neutral and monocharged 9,90-spirobifluorene
The geometries of neutral 9,90-spirobifluorene and of its single charged cation and anion are optimized at B3LYP/6-31G* level of theory. Their electronic structure is described in terms of Mulliken and QTAIM (Quantum-Theory-of-Atoms-in-Molecule) population analysis. Whereas neutral and cationic species belong to D2d symmetry group, the fluorene units in their anionic counterpart are nonequivalent (C2v symmetry group) due to Jahn–Teller effect. The oxidation of the neutral molecule is less advantageous than its reduction. Both these processes decrease the aromaticity of hexagonal carbon rings. The geometry and electron structure changes during the oxidation of the neutral molecule are symmetrically distributed within both fluorene units, analogous changes related to the reduction are concentrated to one of these units only.
The Journal of Chemical Physics
Vibronic coupling in the first eight electronic excited states of Pentafluorobenzene (PFBz) is investigated in this article. In particular, the vibronic coupling between the optically bright ππ* and optically dark πσ* states of PFBz is considered. A model 8 × 8 diabatic Hamiltonian is constructed in terms of normal coordinate of vibrational modes using the standard vibronic coupling theory and symmetry selection rule. The Hamiltonian parameters are estimated with the aid of extensive ab initio quantum chemistry calculations. The topography of the first eight electronic excited states of PFBz is examined at length, and multiple multi-state conical intersections are established. The nuclear dynamics calculations on the coupled electronic surfaces are carried out from first principles by the wave packet propagation method. Theoretical results are found to be in good accord with the available experimental optical absorption spectrum of PFBz.
Journal of Molecular Structure Theochem, 2003
Geometry optimizations of the ground state of oligofluorenes were carried out at the restricted Hartree -Fock level (RHF/6-31G*). This was followed by the use of the restricted configuration interaction/singles (RCIS/6-31G*) approach to optimize the geometry of the lowest (singlet) excited state (S 1 ). It is found that these molecules are nonplanar in the ground state, whereas they almost reach planarity in their S 1 excited state. CIS calculations produce singlet excitation energies in good agreement with the 0 -0 absorption peaks measured in cyclohexane (differences less than 0.2 eV). The RCIS/6-31G* calculations also show that delocalized first single excited states (CIS) are accompanied by a geometry relaxation in comparison to their ground-state (HF) geometries. The geometry relaxation energies were estimated to be approximately 1 eV for these derivatives. From the CIS vertical transition energies taken at the minimum of the S 1 torsional potentials, the emission energies have been computed. It is found that these transition energies are very close to those determined from the emission spectra measured in cyclohexane. q
Computational study of photoexcited dynamics in bichromophoric cross-shaped oligofluorene
The journal of physical chemistry. A, 2014
The non-adiabatic excited state molecular dynamics (NA-ESMD) approach is applied to investigate photoexcited dynamics and relaxation pathways in a spiro-linked conjugated polyfluorene at room (T = 300 K) and low (T = 10 K) temperatures. This dimeric aggregate consists of two perpendicularly oriented weakly interacting α-polyfluorene oligomers. The negligible coupling between the monomer chains results in an initial absorption band composed of equal contributions of the two lowest excited electronic states, each localized on one of the two chains. After photoexcitation, an efficient ultrafast localization of the entire electronic population to the lowest excited state is observed on the time scale of about 100 fs. Both internal conversion between excited electronic states and vibronic energy relaxation on a single electronic state contribute to this process. Thus, photoexcited dynamics of the polyfluorene dimer follows two distinct pathways with substantial temperature dependence on ...
Spirobifluorene Dimers: Understanding How The Molecular Assemblies Drive The Electronic Properties
Advanced Functional Materials, 2021
The spirobifluorene (SBF) is one of the most important scaffold used in the design of Organic SemiConductors (OSCs) for electronics. In recent years, among all the structures developed for these applications, SBF dimers have been highlighted due to their great potentials in Thermally-Activated Delayed Fluorescence and in Phosphorescent Organic Light-Emitting Diodes. Attaching two SBF units generate 10 dimers, each possessing its own structural specificity, which in turn drives its electronic properties. These ten SBF dimers are gathered herein.Understanding how the molecular assembly determines the electronic properties has been one of the pillar of Organic Electronics. This is the
Photophysics of fluorinated benzene. I. Quantum chemistry
The Journal of Chemical Physics, 2010
The electronic structure of energetically low-lying excited singlet states of fluorobenzene molecules is investigated here. Increasing fluorine substitution alters the nature of the excited electronic states and the so-called perfluoro effect is observed for penta-and hexafluorobenzene. Detailed quantum chemistry calculations are carried out at the equation-of-motion coupled-cluster singles and doubles level of theory to establish the potential energy surfaces of the low-lying electronic states of mono-, di-͑orthoand meta-͒, and pentafluorobenzene molecules. A sequence of low-energy conical intersections among the electronic potential energy surfaces is established. It is found that increasing fluorine substitution lowers the energy of the ء electronic state and leads to conical intersections between the S 1 and S 2 electronic states of pentafluorobenzene. Existence of numerous conical intersections among the excited electronic states of these molecules forms the mechanistic details underlying their nonradiative internal conversion. In particular, the slow and biexponential fluorescence emission in pentafluorobenzene is attributed to the existence of low-lying S 1-S 2 conical intersections. The electronic structure data are analyzed in detail and the coupling mechanism among various electronic excited states of mono-, di-, and pentafluorobenzene molecules is established.
Chemical Physics Letters, 2004
Time-dependent density functional theory (TD-DFT) with different functional and related atomic basis sets, is applied to calculate the vertical transitions from the ground to the low-lying valence electronic excited states of hexafluoropropene in vacuum. The results are in satisfactory agreement with the recent high-resolution photoabsorption spectrum of hexafluoropropene in gas phase. The primary photodissociation channel was also studied and the binding energy of the weakest C-F bond of the molecule was determined.