Vibronic interactions and superconductivity in acene anions and cations

Mechanoresponsive Spin via Spin-Lattice Coupling in Organic Cocrystals

The response of crystal structure to external stimuli provides potential applications in the areas of detection, diagnosis, and repair. In this work, we fabricate two allotropic organic cocrystals, with different space groups and lattice parameters, with identical donor and acceptor molecules inside them. Under external stimuli, lattice vibration and electron-phonon coupling present pronounced differences in these two types of crystals, where different strengths of spin polarizations are observed. Furthermore, due to pronounced differences in coupling between lattice and spin inside the allotropic charge transfer crystals, the magnetic field presents a discrepant tunability on both transmission and fluorescence lifetimes. Through decreasing temperature or applying external electric field, the electron-phonon coupling coefficient presents a decreasing tendency, which will affect the dipole and dielectric constant in the allotropic crystals differently.

Exploring vibronic coupling in the benzene radical cation and anion with different levels of the GW approximation

The linear vibronic coupling constants of the benzene radical cation and anion have been obtained with different levels of the GW approximation, including G₀W₀, eigenvalue self-consistent GW, and quasiparticle self-consistent GW, as well as DFT with the following exchange-correlation functionals: BLYP, B3LYP, CAM-B3LYP, tuned CAM-B3LYP, and an IP-tuned CAM-B3LYP functional. The vibronic coupling constants were calculated numerically using the gradients of the eigenvalues of the degenerate HOMOs and LUMOs of the neutral benzene molecule for DFT, while the numerical gradients of the quasiparticle energies were used in the case of GW. The results were evaluated against those of high level wave function methods in the literature, and the approximate self-consistent GW methods and G₀W₀ with long-range corrected functionals were found to yield the best results on the whole.

Electron-Vibration Coupling in Molecular Materials: Assignment of Vibronic Modes from Photoelectron Momentum Mapping

Electron-phonon coupling is one of the most fundamental effects in condensed matter physics. We here demonstrate that photoelectron momentum mapping can reveal and visualize the coupling between specific vibrational modes and electronic excitations. When imaging molecular orbitals with high energy resolution, the intensity patterns of photoelectrons of the vibronic sidebands of molecular states show characteristic changes due to the distortion of the molecular frame in the vibronically excited state. By comparison to simulations, an assignment of specific vibronic modes is possible, thus providing unique information on the coupling between electronic and vibronic excitation.

Investigation of crystal structure, vibrational characteristics and molecular conductivity of 2,3-dichloro-5,6-dicyno-p-benzoquinone

Molecular geometries and vibrational spectra for the ground state of 2,3-dichloro-5,6-dicyno-p-benzoquinone (DDQ) and its anion (DDQ(-)) were computed using DFT method at the B3LYP level employing 6-311++G(d,p) basis set whereas for the first excited state (DDQ(∗)), these were calculated using TD-DFT at the B3LYP level employing the 6-311++G(d,p) basis set available with the Gaussian 09 package. The spectra have been experimentally investigated and the observed IR and Raman bands have been assigned to different normal modes on the basis of the calculated potential energy distributions (PEDs). XRD of single crystal has been investigated to determine molecular and crystal structures of DDQ. In order to elucidate the transfer of electrons, electronic structure and electronic absorption have been calculated with the TD-DFT method. Vibronic interaction and its role in the appearance of superconductivity in the DDQ, DDQ(-) and DDQ(∗) molecules have been investigated. The present XRD, molecular, electronic and vibronic studies indicate that mainly the ag C=O stretching and ring stretching modes participate in the charge transfer process.

DFT study of vibronic properties of d8 (Ni-, Pd-, and Pt-) phthalocyanines

By means of density functional theory, we have studied the electronic structure and vibronic properties of single neutral NiPc, PdPc, and PtPc molecules and their singly and doubly ionized cations and anions. In particular, the vibronic couplings and reorganization energies of all systems are compared. Partitioning of the reorganization energy, corresponding to the photoelectron spectra of the first and second ionizations of studied molecules, into normal mode contributions shows that the major contributions are due to several vibrational modes with a(1g) symmetry and energies lower than 1600 cm(-1). The results reveal that the reorganization energy due to the singly positive ionization in the studied molecules is up to about one order of magnitude less than other reorganization energies. This makes these metal phthalocyanines, from the perspective of intramolecular reorganization energies, attractive as electron donor for intramolecular electron transfer in electron acceptor-donor systems.

Strong intramolecular electron-phonon coupling in the negatively charged aromatic superconductor picene

Superconductivity was recently discovered in solid potassium-intercalated picene (K(3)22ph), in which the picene molecule becomes trianionic (22ph(3-)). In this Letter, we conduct a theory-based study of the superconductivity of 22ph(3-) within the framework of BCS theory. We estimate the density of states N(ε(F)) on the Fermi level to be 2.2 states per (eV molecule spin) by using the theoretical intramolecular electron-phonon coupling l(x) and the experimental superconducting transition temperature T(c) of 18 K. The theoretical value is consistent with the 1.2 states per (eV molecule spin) determined experimentally for K(3)22ph with T(c)=18 K, indicating the validity of our theoretical treatment and the electron-phonon mechanism for superconductivity. The predicted l(x), 0.206 eV, for 22ph(3-) is larger than any value reported for organic superconductors, so picene may have the largest l(x) among the superconductors reported so far.

Evaluation of charge mobility in organic materials: from localized to delocalized descriptions at a first-principles level

The carrier mobility for carbon electronic materials is an important parameter for optoelectronics. We report here some recently developed theoretical tools to predict the mobility without any free parameters. Carrier scatterings with phonons and traps are the key factors in evaluating the mobility. We consider three major scattering regimes: i) where the molecular internal vibration severely induces charge self-trapping and, thus, the hopping mechanism dominates; ii) where both intermolecular and intramolecular scatterings come to play roles, so the Holstein-Peierls polaron model is applied; and, iii) where charge is well delocalized with coherence length comparable with acoustic phonon wavelength, so that a deformation potential approach is more appropriate. We develop computational methods at the first-principles level for the three different cases that have extensive potential application in rationalizing material design.

Mass Spectrometry and Photoelectron Spectroscopy of Tetracene Cluster Anions, (Tetracene) (n = 1−100): Evidence for the Highly Localized Nature of Polarization in a Cluster Analogue of Oligoacene Crystals

Photoelectron spectroscopy of tetracene cluster anions, (tetracene)n- (n = 1-100), reveals the coexistence of two types of isomers, designated as isomers I and II-1 (n = 10-50) or isomers I and II-2 (n > 60), in a wide size range. The vertical detachment energies (VDEs) of isomer I increase persistently due to polarization and structural relaxation effects, where a monomeric anion core is encompassed with geometrically reorganized neutral molecules. Conversely, a characteristic ion distribution in the mass spectrum of (tetracene)n-ensues from the two-dimensional (2D) herringbone-type ordering of isomer II-1, whose VDEs remain constant at 1.80 eV for n >/= 14. Also, isomer II-2, presumably adopting multilayered structural motifs, exhibits invariable VDEs of 2.0 eV, a manifestation of significant charge screening effects in these isomers. The invariable nature of the VDEs of isomers II-1 and II-2 unambiguously demonstrates a largely localized nature of polarization induced by the excess charge residing in microscopic crystal-like environments. Surprisingly, only 14 tetracene molecules within a 2D herringbone-type layer including an excess charge can provide the charge stabilization energy corresponding to approximately 80% of that of the crystal, and the rest of the energy is provided by polarization of neutral molecules in adjacent layers.

Roles of inter- and intramolecular vibrations and band-hopping crossover in the charge transport in naphthalene crystal

We calculate the hole and electron mobilities in naphthalene crystal from 10 to 300 K within the framework of the Holstein-Peierls model coupled with first-principles density-functional-theory-projected tight-binding band structures. All the electron-phonon coupling constants, including both local and nonlocal parts for inter- and intramolecular vibrations, have been taken into considerations through density functional theory. The band-hopping crossover transition temperature for the electron transport in the c' axis is calculated to be around 23 K. We have identified a few high frequency intramolecular vibrations which are very important to the charge transport in naphthalene crystal due to their comparatively large electron-phonon coupling constants. However, their contributions to the temperature dependence of mobility are minor because of the small phonon occupations and small nonlocal coupling strengths. The low frequency intermolecular modes (longitudinal optical modes) are found to be the major contributions to the temperature dependent charge transfer properties in naphthalene crystal. Even though the calculated qualitative temperature dependence is in agreement with experiment, the predicted absolute mobility is about one to two orders of magnitude larger.

Electron−Phonon Interactions and Intra- and Intermolecular Charge Mobility in the Monocations of Annulenes

Possible electron pairing in pi-conjugated positively charged annulenes such as (CH)(18) (18an) and (CH)(30) (30an) is studied and compared with that in the positively charged acenes. The total electron-phonon coupling constants in the monocations (l(HOMO)) for 18an and 30an are estimated. The E(2g) modes of 1611 and 1201 cm(-1) most strongly couple to the highest occupied molecular orbitals (HOMO) in 18an and 30an, respectively. The l(HOMO) values for annulenes are larger than those for acenes. The phase pattern difference between the HOMO of acenes localized on the edge part of carbon atoms and the delocalized HOMO of annulenes is the main reason for the calculated results. In view of the calculated results of the l(HOMO) values, intramolecular electron mobility (sigma(intra,HOMO)), and the reorganization energies (RE(HOMO)) in the positively charged molecules, the monocations of annulenes cannot easily become good conductors compared with the monocations of acenes, but the condition of the attractive electron-electron interactions is realized more easily in the monocations of annulenes than in the monocations of acenes. The hypothetical intramolecular supercurrent originating from both intramolecular and intermolecular vibrations in the monocations of annulenes and acenes in a case where the distance between two adjacent molecules is too large for the molecular crystal to become normal metallic state, is also discussed.

Vibronic Coupling in the Ground and Excited States of Oligoacene Cations

The vibrational coupling in the ground and excited states of positively charged naphthalene, anthracene, tetracene, and pentacene molecules is studied on the basis of a joint experimental and theoretical study of ionization spectra using high-resolution gas-phase photoelectron spectroscopy and first-principles correlated quantum-mechanical calculations. Our theoretical and experimental results reveal that, while the main contribution to relaxation energy in the ground state of oligoacene systems comes from high-energy vibrations, the excited-state relaxation energies show a significant redistribution toward lower-frequency vibrations. A direct correlation is found between the nature of the vibronic interaction and the pattern of the electronic state structure.

Vibronic coupling in benzene cation and anion: Vibronic coupling and frontier electron density in Jahn-Teller molecules

Vibronic coupling constants of Jahn-Teller molecules, benzene radical cation and anion, are computed as matrix elements of the electronic part of the vibronic coupling operator using the electronic wave functions calculated by generalized restricted Hartree-Fock and state-averaged complete active space self-consistent-field methods. The calculated vibronic coupling constants for benzene cation agree well with the experimental and theoretical values. Vibronic coupling density analysis, which illustrates the local properties of the coupling, is performed in order to explain the order of magnitude of the coupling constant from view of the electronic and vibrational structures. This analysis reveals that the couplings of the e2g2 and e2g3 modes in which the large displacements locate on C-C bonds are strong in the cation. On the other hand, they are greatly weakened in the anion because of the decrease of electron density in the region of the C-C bonds, which originates from the antibonding nature of the singly occupied molecular orbital of the anion. However, the difference of the electronic structure has a little influence on the vibronic coupling of the e2g4 mode. These results indicate that the vibronic coupling depends not only on the direction of the nuclear displacement but also on the frontier electron density.

Electron-phonon interactions in the monocations of polyacetylenes

Electron-phonon interactions in the monocations of trans-polyacetylenes such as C2H4 (2tpa), C4H6 (2tpa), C6H8 (6tpa), and C8H10 (8tpa) are studied. The C-C stretching Ag modes around 1700 cm(-1) afford the largest electron-phonon coupling constants in the monocations of polyacetylenes. However, the C-C bending Ag modes around 1200 cm(-1) afford much smaller electron-phonon coupling constants than the C-C stretching Ag modes around 1700 cm(-1) in the monocations of polyacetylenes. The total electron-phonon coupling constants for the monocations (l HOMO) are estimated to be 0.357, 0.285, 0.281, and 0.279 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. The l HOMO values for polyacetylenes with C 2h geometry hardly change with an increase in molecular size while those for polyacenes with D 2h geometry significantly decrease with an increase in molecular size. The l HOMO values for polyacetylenes are larger than those for polyacenes. The calculated results are rationalized in terms of the phase patterns of the molecular orbitals in detail. The electron transfer in the positively charged polyacetylenes is also discussed. Intramolecular electron mobility (sigma(intra,monocation)) in the positively charged polyacetylenes is estimated to be smaller than those for the positively charged polyacenes. The reorganization energies for the positively charged polyacetylenes are estimated to be larger than those for the positively charged polyacenes. Thus, the larger overlap integrals between two neighboring molecules are needed for the positively charged polyacetylenes to become good conductor than those for positively charged polyacenes. On the other hand, the conditions under which the electron-electron interactions are attractive are more easily realized in the monocations of polyacetylenes than in the monocations of polyacenes. The quality as conducting materials would not significantly depend on the molecular size in the positively charged polyacetylenes, compared with that in the positively charged polyacenes. Multimode problem is also treated in order to investigate how consideration of multimode problem is closely related to the characteristics of the electron-phonon interactions.

Electron−Phonon Interactions and Jahn−Teller Effects in the Monocation of Corannulene

Electron-phonon interactions in the monocation of corannulene are studied by using the hybrid Hartree-Fock (HF)/density-functional-theory (DFT) method in the Gaussian 98 program package. The C-C stretching mode of 1498 cm(-1) most strongly couples to the e1 highest occupied molecular orbitals (HOMO) in corannulene. The total electron-phonon coupling constant for the monocation (l(HOMO)) of corannulene is estimated to be 0.165 eV. The l(HOMO) value for corannulene is much larger than those for coronene and acenes with similar numbers of carbon atoms. The delocalized electronic structures and the intermediate characteristics between the strong sigma-orbital interactions and weak pi-orbital interactions originating from a bowl-shaped C(5v) geometry are the main reason that the l(HOMO) value for corannulene is much larger than those for planar D(6h) symmetric pi-conjugated coronene and D(2h) symmetric pi-conjugated acenes with similar numbers of carbon atoms. The electron transfer in the positively charged corannulene is also discussed. Intramolecular electron mobility (sigma(intra,monocation)) in the positively charged corannulene is estimated to be smaller than those for the positively charged pi-conjugated acenes and coronene. The reorganization energy for the positively charged corannulene (0.060 eV) is estimated to be larger than those for the positively charged acenes and coronene. The strong orbital interactions between two neighboring carbon atoms in the HOMO of corannulene with the bowl-shaped structure are the main reasons for the calculated results. Thus, the larger overlap integral between two neighboring molecules is needed for the positively charged corannulene to become a better conductor than those for positively charged coronene and acenes. The smaller density of states at the Fermi level n(0) values are enough for the conditions of the attractive electron-electron interactions to be realized in the monocation of corannulene than in the monocations of coronene and acenes with similar numbers of carbon atoms. The multimode problem is also treated in order to investigate how consideration of the multimode problem is closely related to the characteristics of the electron-phonon interactions.

Vibronic interactions and possible electron pairing in positively charged cyanodienes

The conditions under which the attractive electron-electron interactions are realized in the monocations of sigma-conjugated cyanodienes such as C(6)N(4)H(4), C(8)N(6)H(4), and C(10)N(8)H(4) and of pi-conjugated acenes are discussed. The total electron-phonon coupling constants for the monocations l(HOMO) of cyanodienes are much larger than those for the monocations of acenes. The strong sigma orbital interactions between two neighboring atoms in the highest occupied molecular orbitals (HOMO) of sigma-conjugated cyanodienes are the main reason for the calculated results. Furthermore, we discuss how the conditions under which the monocation crystals become good conductor are related to the molecular size. Both the l(HOMO) values and the reorganization energies between the neutral molecules and the monocations decrease with an increase in molecular size in cyanodienes. The calculated results for the sigma-conjugated cyanodienes are compared with those for the pi-conjugated acenes in order to investigate how the CH-N substitutions in cyanodienes are closely related to the l(HOMO) values and the reorganization energies. Both the l(HOMO) and the reorganization energies in the positively charged sigma-conjugated cyanodienes are much larger than those in the positively charged pi-conjugated acenes. This means that in order to become good conductors, the positively charged sigma-conjugated cyanodienes need larger overlap integral between two adjacent molecules than the positively charged pi-conjugated acenes. On the other hand, since the l(HOMO) values for cyanodienes are much larger than those for acenes, the condition of attractive electron-electron interactions is more easily to be realized in the monocations of cyanodienes than in the monocations of acenes. It is suggested that the positively charged sigma-conjugated cyanodienes cannot easily become good conductors, but the conditions under which the electron-electron interactions become attractive are realized more easily in the positively charged sigma-conjugated cyanodienes than in the positively charged pi-conjugated acenes.

Electron-phonon interactions in photoinduced excited electronic states in fluoroacenes

The electron-phonon coupling constants [l(B1u(HOMO-->LUMO))] in the photoinduced excited electronic states in fluoroacenes are estimated and compared with those in the monoanions (l(LUMO)) and cations (l(HOMO)). The l(B1u(HOMO-->LUMO)) values are much larger than the l(LUMO) and l(HOMO) values in fluoroacenes. Furthermore, the Coulomb pseudopotential mu* values for the excited electronic states are estimated to be smaller than those for the monoanions and cations. The complete phase patterns difference between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) is the main reason why the electron-phonon coupling constants and the mu* values are larger and smaller, respectively, in the photoinduced excited electronic states than in the monoanions and cations. The possible electron pairing and Bose-Einstein condensation in the excited electronic states of fluoroacenes are discussed. Because of larger electron-phonon coupling constants and smaller mu* values in the excited electronic states than in the charged states, the conditions under which the electron-electron interactions become attractive can be more easily realized, in principle, in the excited electronic states than in the charged states in fluoroacenes. The l(B1u(HOMO-->LUMO)) values hardly change by H-F substitution, even though the l(LUMO) and l(HOMO) values significantly increase by H-F substitution in acenes. Antibonding interactions between carbon and fluorine atoms in the HOMO and LUMO are the main reason why the l(B1u(HOMO-->LUMO)) values hardly change by H-F substitution in acenes.

Vibronic Interactions and Possible Electron Pairing in the Photoinduced Excited Electronic States in Molecular Systems: A Theoretical Study

Electron-phonon interactions in the photoinduced excited electronic states in molecular systems such as phenanthrene-edge-type hydrocarbons are discussed and compared with those in the monoanions and cations. The complete phase patterns difference between the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) (the atomic orbitals between two neighboring carbon atoms combined in phase (out of phase) in the HOMO are combined out of phase (in phase) in the LUMO) are the main reason that the C-C stretching modes around 1500 cm(-1) afford much larger electron-phonon coupling constants in the excited electronic states than in the charged electronic states. The frequencies of the vibrational modes that play an essential role in the electron-phonon interactions for the excited electronic states are similar to those for the monoanions and cations in phenanthrene-edge-type hydrocarbons. Possible electron pairing and Bose-Einstein condensation in the photoinduced excited electronic states as well as those in the monoanions and cations in molecular systems such as phenanthrene-edge-type hydrocarbons are also discussed.

Vibronic Interactions in Negatively Charged Polyacetylene

Electron-phonon interactions in the monoanions of polyacetylenes such as C2H4 (2tpa), C4H6 (4tpa), C6H8 (6tpa), and C8H10 (8tpa) are studied and compared with those in the monoanions of polyacenes. The C-C stretching A(g) modes around 1500 cm(-1) the most strongly couple to the lowest unoccupied molecular orbitals (LUMO) in polyacetylenes. The estimated total electron-phonon coupling constants for the monoanions (l(LUMO)) are 0.579, 0.555, 0.463, and 0.401 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. The l(LUMO) values for polyacetylenes are much larger than those for polyacenes. Furthermore, the l(LUMO) value for polyacetylene with C(2h) geometry is estimated to be 0.254 eV, and is larger than that (0.024 eV) for polyacene with D(2h) geometry. The phase patterns difference between the LUMO of polyacenes localized on the edge part of carbon atoms, and the delocalized LUMO of polyacetylenes is the main reason for the calculated results. The single charge transfer through the molecule in polyacetylenes are also discussed. The reorganization energies between the neutral molecule and the corresponding monoanion are estimated to be 0.164, 0.144, 0.125, and 0.113 eV for 2tpa, 4tpa, 6tpa, and 8tpa, respectively. Such reorganization energy decreases with an increase in molecular size. The conditions under which the attractive electron-electron interactions are realized in the monoanions of polyacetylenes and polyacenes are discussed. In terms of the electron-phonon interactions and the reorganization energies, the relationships between the normal and possible superconducting states are briefly discussed. We find that the monoanions with smaller molecular size cannot easily become good conductors, however, the conditions under which the interactions between two electrons are attractive are more easily realized in the monoanions with smaller molecular size than in the monoanions with larger molecular size.

The essential role of H-F substitution in the electron-phonon interactions and electron transfer in the negatively charged acenes

The single charge transfer through acenes, partially H-F substituted acenes, and fluoroacenes is discussed. The reorganization energies between the neutral molecules and the corresponding monoanions for partially H-F substituted acenes lie between those for acenes and fluoroacenes. The delocalization of the lowest unoccupied molecular orbitals (LUMO) by substituting hydrogen atoms by fluorine atoms with the highest electronegativity in every element is the main reason why the reorganization energy between the neutral molecule and the monoanion for partially H-F substituted acenes lies between those for acenes and fluoroacenes. This result implies that the negatively charged partially H-F substituted acenes would be better conductors with rapid electron transfer than the negatively charged fluoroacenes if we assume that the overlap of the LUMO between partially H-F substituted acenes is not significantly different from that between two neighboring fluoroacenes. The structures of the monoanions of acenes, fluoroacenes, and partially H-F substituted acenes are optimized under D2h geometry, and the Jahn-Teller effects in the monoanions of benzene and fluorobenzene are discussed. The vibration effect onto the charge transfer problem is also discussed. The C-C stretching modes around 1500 cm(-1) are the main modes converting the neutral molecules to the monoanions in acenes, fluoroacenes, and partially H-F substituted acenes. It can be confirmed from the calculational results that the C-C stretching modes around 1500 cm(-1) the most strongly couple to the LUMO in these molecules. The main reason why the total electron-phonon coupling constants (lLUMO) for the monoanions of acenes in which four outer hydrogen atoms are substituted by fluorine atoms are larger than those for the monoanions of acenes in which several inner hydrogen atoms are substituted by fluorine atoms is suggested. The relationships between the electron transfer and the electron-phonon interactions are discussed. The plot of the reorganization energies against the lLUMO values is found to be nearly linear. In view of these results, the relationships between the normal and superconducting states are briefly discussed.

Characterization of the molecular parameters determining charge transport in anthradithiophene

The molecular parameters that govern charge transport in anthradithiophene (ADT) are studied by a joint experimental/theoretical approach involving high-resolution gas-phase photoelectron spectroscopy and quantum-mechanical methods. The hole reorganization energy of ADT has been determined by an analysis of the vibrational structure of the lowest ionization band in the gas-phase photoelectron spectrum as well as by density-functional theory calculations. In addition, various dimers and clusters of ADT molecules have been considered in order to understand the effect of molecular packing on the hole and electron intermolecular transfer integrals. The results indicate that the intrinsic electronic structure, the relevant intramolecular vibrational modes, and the intermolecular interactions in ADT are very similar to those in pentacene.

A multimode analysis of the gas-phase photoelectron spectra in oligoacenes

We present a multimode vibrational analysis of the gas-phase ultraviolet photoelectron spectra of the first ionization in anthracene, tetracene, and pentacene, using electron-vibration constants computed at the density functional theory level. The first ionization of each molecule exhibits a high-frequency vibronic structure; it is shown that this regularly spaced feature is actually the consequence of the collective action of several vibrational modes rather than the result of the interaction with a single mode. We interpret this feature in terms of the missing mode effect. We also discuss the vibronic coupling constants and relaxation energies obtained from the fit of the photoelectron spectra with the linear vibronic model.

Inverse isotope effects and electron-phonon coupling in the positively charged deutero- and fluoroacenes

Electron-phonon interactions in the monocations of deutero- and fluoroacenes are studied and compared with those in the monocations of acenes and those in the monoanions of fluoroacenes. Because of the significant phase pattern difference between the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO), the frequency modes lower than 500 cm(-1) and the high-frequency modes around 1400 cm(-1) couple more strongly to the LUMO than to the HOMO, while the frequency modes around 500 cm(-1) and the frequency modes around 1600 cm(-1) couple more strongly to the HOMO than to the LUMO in fluoroacenes with D2h geometry. The total electron-phonon coupling constants for the monocations (l(HOMO)) are estimated and compared with those for the monoanions (l(LUMO)) in deutero- and fluoroacenes. The l(HOMO) values are estimated to be 0.418, 0.399, 0.301, 0.255, and 0.222 eV for C6F6 (1f), C10F8 (2f), C14F10 (3f), C18F12 (4f), and C22F14 (5f), respectively. The l(HOMO) values are smaller than the l(LUMO) values in small fluoroacenes. But the l(HOMO) value decreases with an increase in molecular size less rapidly than the l(LUMO) value in fluoroacenes, and the l(HOMO) value of 0.074 eV is much larger than the l(LUMO) value of 0.009 eV in polyfluoroacene. The logarithmically averaged phonon frequencies for the monocations (omega(ln,HOMO)) are estimated to be larger than those for the monoanions (omega(ln,LUMO)) in fluoroacenes. This is because the C-C stretching modes around 1600 cm(-1) couple most strongly to the HOMO, and those around 1400 cm(-1) couple the most strongly to the LUMO in fluoroacenes. The significant phase pattern difference between the HOMO and the LUMO is the main reason for the calculational results. The l(HOMO) values increase much more significantly by H-F substitution than by H-D substitution in acenes. The possible inverse isotope effects in the electron-phonon interactions as a consequence of deuteration in the monocations of nanosized molecules are suggested.