Electronic States of Aromatic Hydrocarbons: The Franck-Condon Principle and Geometries in Excited States

1962 ◽  
Vol 15 (4) ◽  
pp. 573 ◽  
Author(s):  
EF McCoy ◽  
IG Ross
Keyword(s):  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Strain Energy ◽  
Electronic Transitions ◽  
Bond Orders ◽  
Polycyclic Aromatics ◽  
Aromatic Rings ◽  
Bond Strain ◽  
Length Changes ◽  
Franck Condon

It is suggested that electronic transitions in aromatic hydrocarbons can profitably be characterized by a quantity R, where R2 is the sum of the squares of the bond length changes accompanying the transition. R determines, via the Franck-Condon principle, the distribution of intensity within the vibrational envelope of a transition. In polycyclic aromatics, values of R can be extracted from solution spectra, if the intervals of about 1400 cm-1 which commonly separate the vibrational peaks are interpreted as defining quasi-progressions in a skeletal bond displacement vibration. Values of R so determined are compared with values computed from bond orders in excited states, using the wave-functions of Pariser. Such comparisons are made for benzene, naphthalene, azulene, and anthracene. Agreement is good. The calculated bond orders are tabulated. In an Appendix, bond angles in aromatic rings are calculated on the assumption that the observed angles minimize the σ-bond strain energy. Angles are calculated for the ground states of naphthalene and anthracene, and for two excited states of naphthalene. The excited state geometries so deduced are depicted.

Abinitio calculation of the vibrational structure in the electronic spectra of HCN and DCN between 1700 and 2000 Å

1977 ◽  
Vol 55 (20) ◽  
pp. 3664-3675 ◽  
Author(s):  
M. Perić ◽  
S. D. Peyerimhoff ◽  
R. J. Buenker
Keyword(s):  
Excited States ◽  
Band System ◽  
Vibrational Structure ◽  
Electronic Transitions ◽  
Dissociation Limit ◽  
Potential Surfaces ◽  
Double Zeta ◽  
Polarization Functions ◽  
Franck Condon ◽  
Ci Calculations

Ab initio SCF and CI calculations for the potential surfaces of HCN in ground and various 1(π,π*) excited states are carried out using an AO basis of double-zeta quality augmented with various polarization functions. These results are then combined with transition moment data to allow for a Franck-Condon analysis of the vibrational structure of the lowest three electronic transitions in both HCN and DCN. The resulting intensity distribution is then compared with the corresponding experimental data reported by Herzberg and Innes. This work confirms the earlier conclusion of Schwenzer et al. that the upper state in the [Formula: see text] band system is the 1∑−−1A″species, and not the 1Δ as originally believed. In addition a detailed mechanism for the observed predissociation of the α state is outlined, in which the gradual conversion of the π* MO of bent HCN into a pure hydrogenic 1s AO plays a key role. Arguments are also presented in favor of assigning the [Formula: see text]transition seen in DCN to a 1Δ-21A′ upper state with the same D + CN dissociation limit as for the 1∑−−1A″ species.

scholarly journals Excited States Symmetry Breaking and In-Plane Polarization Cause Chiral Reversal in Diastereomers

Molecules ◽  
2021 ◽  
Vol 26 (15) ◽  
pp. 4680
Author(s):  
Chenglong Wang ◽  
Jingang Wang ◽  
Chunyang Wang
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Symmetry Breaking ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Physical Mechanism ◽  
Electromagnetic Interaction ◽  
Electronic Transitions ◽  
Conjugated Systems ◽  
Polycyclic Aromatic

In this work, we investigate the electronic transitions and chirality of three isomers of huge conjugated systems: asymmetric diastereomers (MMMM) and two symmetrical diastereomers (PMPM and PPMM). The physical mechanism of flipping has been studied theoretically. The new ribbon-shaped polycyclic aromatic hydrocarbons (PAHs) molecule is formed by connecting three graphene-like systems with large conjugated π orbitals. By calculating and analyzing electromagnetic interaction decomposition over distance, it can be found that the chirality reversal of different energies is caused by the symmetrical fracture of TMDM in the Z direction. The chirality reversal at the same energy is caused by the in-plane polarization of the TMDM along the Y direction.

The Character of Low-Lying Excited States of Mixed-Ligand Metal Carbonyls. TD-DFT and CASSCF/CASPT2 Study of [W(CO)4L] (L = ethylenediamine, N,N'-dialkyl-1,4-diazabutadiene) and [W(CO)5L] (L = pyridine, 4-cyanopyridine)

2003 ◽  
Vol 68 (1) ◽  
pp. 89-104 ◽  
Author(s):  
Stanislav Záliš ◽  
Antonín Vlček ◽  
Chantal Daniel
Keyword(s):  
Excited States ◽  
Substitution Effect ◽  
Electronic Transitions ◽  
Ligand Field ◽  
Metal Carbonyls ◽  
Electron Density Redistribution ◽  
Time Resolved ◽  
Model Complex ◽  
Td Dft ◽  
Time Resolved Infrared Spectroscopy

This contribution presents the results of the TD-DFT and CASSCF/CASPT2 calculations on [W(CO)4(MeDAB)] (MeDAB = N,N'-dimethyl-1,4-diazabutadiene), [W(CO)4(en)] (en = ethylenediamine), [W(CO)5(py)] (py = pyridine) and [W(CO)5(CNpy)] (CNpy = 4-cyanopyridine) complexes. Contrary to the textbook interpretation, calculations on the model complex [W(CO)4(MeDAB)] and [W(CO)5(CNpy)] show that the lowest W→MeDAB and W→CNpy MLCT excited states are immediately followed in energy by several W→CO MLCT states, instead of ligand-field (LF) states. The lowest-lying excited states of [W(CO)4(en)] system were characterized as W(COeq)2→COax CT excitations, which involve a remarkable electron density redistribution between axial and equatorial CO ligands. [W(CO)5(py)] possesses closely-lying W→CO and W→py MLCT excited states. The calculated energies of these states are sensitive to the computational methodology used and can be easily influenced by a substitution effect. The calculated shifts of [W(CO)4(en)] stretching CO frequencies due to excitation are in agreement with picosecond time-resolved infrared spectroscopy experiments and confirm the occurrence of low-lying M→CO MLCT transitions. No LF electronic transitions were found for either of the complexes studied in the region up to 4 eV.

scholarly journals Exploitation of Baird Aromaticity and Clar’s Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

Chemistry ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 532-549
Author(s):  
Felix Plasser
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Materials Science ◽  
Chemical Shifts ◽  
Qualitative Description ◽  
Triplet States ◽  
Excitation Energies ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four biphenylene-derived PAHs finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). The results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

scholarly journals Exploitation of Baird Aromaticity and Clar's Rule for Tuning the Triplet Energies of Polycyclic Aromatic Hydrocarbons

2021 ◽  
Author(s):  
Felix Plasser
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Density Functional ◽  
Materials Science ◽  
Chemical Shifts ◽  
Qualitative Description ◽  
Triplet States ◽  
Excitation Energies ◽  
Polycyclic Aromatic

Polycyclic aromatic hydrocarbons (PAH) are a prominent substance class with a variety of applications in molecular materials science. Their electronic properties crucially depend on the bond topology in ways that are often highly non-intuitive. Here, we study, using density functional theory, the triplet states of four PAHs based on the biphenylene motif finding dramatically different triplet excitation energies for closely related isomeric structures. These differences are rationalised using a qualitative description of Clar sextets and Baird quartets, quantified in terms of nucleus independent chemical shifts, and represented graphically through a recently developed method for visualising chemical shielding tensors (VIST). These results are further interpreted in terms of a 2D rigid rotor model of aromaticity and through an analysis of the natural transition orbitals involved in the triplet excited states showing good consistency between the different viewpoints. We believe that this work constitutes an important step in consolidating these varying viewpoints of electronically excited states.

Selective dealkylation of alkyl polycyclic aromatic hydrocarbons towards innovative upgrading process of practical heavy oil

2021 ◽  
Author(s):  
Fumiya Nakano ◽  
Tomohide Goma ◽  
Satoshi Suganuma ◽  
Etsushi Tsuji ◽  
Naonobu Katada
Keyword(s):  
Polycyclic Aromatic Hydrocarbons ◽  
Pore Size ◽  
Aromatic Hydrocarbons ◽  
Heavy Oil ◽  
Acid Sites ◽  
Polycyclic Aromatics ◽  
Large Pore ◽  
Polycyclic Aromatic ◽  
Long Chain ◽  
Large Pore Size

A silica-monolayer loaded on alumina with weak Brønsted acid sites and large pore size can selectively dealkylate alkyl polycyclic aromatics to long-chain alkanes and polycyclic aromatics for production of chemicals and fuel.

Bonding and electronic states of boron in silicon nanowires characterized by an infrared synchrotron radiation beam

Nanoscale ◽  
2015 ◽  
Vol 7 (16) ◽  
pp. 7246-7251 ◽  
Author(s):  
N. Fukata ◽  
W. Jevasuwan ◽  
Y. Ikemoto ◽  
T. Moriwaki
Keyword(s):  
Synchrotron Radiation ◽  
Excited States ◽  
Silicon Nanowires ◽  
Ground State ◽  
Electronic States ◽  
Electronic Transitions ◽  
Synchrotron Radiation Beam ◽  
Radiation Beam ◽  
Acceptor Atom ◽  
Ft Ir

The first report of B local vibrational peaks and electronic transitions of a bound hole from the ground state of a B acceptor atom to excited states by means of micro-FT-IR measurements using an IR-SR beam.

scholarly journals Ultrafast dynamics in polycyclic aromatic hydrocarbons: the key case of conical intersections at higher excited states and their role in the photophysics of phenanthrene monomer

2019 ◽  
Vol 21 (31) ◽  
pp. 16981-16988 ◽  
Author(s):  
M. Nazari ◽  
C. D. Bösch ◽  
A. Rondi ◽  
A. Francés-Monerris ◽  
M. Marazzi ◽  
...  
Keyword(s):  
Excited State ◽  
Excited States ◽  
Aromatic Hydrocarbons ◽  
Ultrafast Dynamics ◽  
Simultaneous Presence ◽  
Conical Intersections ◽  
Polycyclic Aromatic ◽  
Adiabatic Transitions ◽  
Proper Interpretation ◽  
Higher Excited States

Proper interpretation of phenanthrene's and similar PAHs’ photocycle relies on two higher excited state relaxations due to the simultaneous presence of non-adiabatic and adiabatic transitions.

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