Tokio Yamabe

Vibronic interactions and superconductivity in acene anions and cations

Vibronic interaction and its role in the occurrence of superconductivity in the monoanions and cations of benzene and acenes are studied. The vibrational frequencies and the vibronic coupling constants for benzene and acenes are computed and analyzed and electron—phonon coupling constants in the monoanions and cations are evaluated. The C–C stretching E2g mode of 1656u200acm−1 affords large electron—phonon coupling constants in the monoanion and cation of benzene. The C–C stretching Ag modes of 1400–1600u200acm−1 and the lowest frequency Ag mode play an important role in the electron–phonon coupling in the monoanions of acenes, while the only C–C stretching Ag modes of 1400–1600u200acm−1 afford large electron–phonon coupling constants in the monocations of acenes. We estimate possible superconducting transition temperatures Tcs for the monoanions and cations of benzene and acenes. The predicted Tcs for the monocations of benzene and acenes are much lower than those for the monoanions. Possible high-temperature superc...

Electron–intramolecular-phonon coupling and possible superconductivity in negatively charged coronene and corannulene

Electron–intramolecular-phonon coupling and its role in the occurrence of possible superconductivity in the monoanions of coronene (C24H12) and corannulene (C20H10) are studied. Electron–intramolecular-phonon coupling constants are calculated from the intramolecular vibronic coupling constants. The C–C stretching E2g mode of 1668 cm−1 plays an essential role in the electron–intramolecular-phonon coupling in the monoanion of coronene while the low frequency E2 modes, which have a radial character, and the C–C stretching mode of 1669 cm−1, which has a tangential character, afford large electron–intramolecular-phonon coupling constants in the monoanion of corannulene. The calculated total electron–intramolecular-phonon coupling constant for the monoanion of corannulene (0.269 eV) is much larger than that for coronene monoanion (0.076 eV). The intermediate characteristics between σ and π orbital interaction properties owing to the bowl-shaped structure of corannulene make orbital interactions between two neig...

Electron–phonon interactions in the monoanions of fluoroacenes

Electron–phonon interactions in the monoanions of fluoroacenes such as C6F6u200a(1f), C10F8u200a(2f), C14F10u200a(3f), C18F12u200a(4f), and C22F14u200a(5f) are studied, and compared with those in the monoanions of acenes and deutero-acenes. The C–C stretching modes around 1500 cm−1 the most strongly couple to the lowest unoccupied molecular orbitals (LUMO) in fluoroacenes. The estimated total electron–phonon coupling constants (lLUMO) are 0.475, 0.473, 0.350, 0.273, and 0.215 eV for 1f, 2f, 3f, 4f, and 5f, respectively. The lLUMO values for fluoroacenes are much larger than those for acenes and deutero-acenes. Possible superconducting transition temperatures (Tcs) for the monoanions of deutero-acenes and fluoroacenes are estimated to be larger than those for the monoanions of acenes. The transition temperature (Tc) value increases much more significantly by H–F substitution than by H–D substitution in acenes. The lLUMO and Tc values significantly decrease with an increase in molecular size from the monoanions of 1f to 5f. Th...

Electron–phonon coupling in negatively charged cubane and octasilacubane

Electron–phonon coupling in the monoanions of cubic molecules such as cubane (CH)8 and octasilacubane (SiH)8 (cubane-series) are studied. The vibrational frequencies and the orbital vibronic coupling constants are computed and analyzed and the electron–phonon coupling constants are estimated. The results for cubane-series are compared with those for acene- (acene-series) and phenanthrene-edge-type hydrocarbons (phenanthrene-series). The T2g modes of 687 and 848 cm−1, the Eg modes of 922 and 1125 cm−1, and the A1g mode of 1021 cm−1 strongly couple to the t1u lowest unoccupied molecular orbital (LUMO) in cubane, on the other hand, only T2g mode of 197 cm−1 and the Eg mode of 403 cm−1 strongly couple to the t1u LUMO in octasilacubane. The calculated total electron–phonon coupling constant for the monoanion of cubane (0.495 eV) is much larger than that for the monoanion of octasilacubane (0.262 eV). The relationships between the HOMO–LUMO gaps and the total electron–phonon coupling constants in the monoanions...

Molecular concepts of normal and superconducting states in acenes and B, N-substituted acenes: A theoretical study

Electron–phonon coupling and the normal and possible superconducting states in the monoanions of B, N-substituted acenes such as B3N3H6, B5N5H8, and B7N7H10 are studied. The results for B, N-substituted acenes are compared with those for acenes. The B–N stretching modes around 1500 cm−1 and the low-frequency modes, less and more, respectively, strongly couple to the lowest unoccupied molecular orbitals (LUMO) with an increase in molecular size from B3N3H6 to B7N7H10. The relationship between the intrinsic intramolecular conductivity and the intramolecular electronic structures is investigated, and it is found that the intrinsic high conductivity needs small energy difference between the highest occupied molecular orbitals and the LUMO, the high frequency modes which play an essential role in the electron–phonon interactions, and large number of atoms. The relationship between the normal and superconducting states in acenes is compared with that in B, N-substituted acenes. Both possible superconducting tra...

Superconductivity in acenes

Abstract The vibronic coupling between the lowest unoccupied molecular orbital (LUMO) and molecular vibrations is calculated and analyzed with respect to a series of acenes. The Raman active Cue5f8C stretching modes of 1400–1600xa0cm −1 have large coupling constants in small acenes, while both low Raman active modes of 200–300xa0cm −1 and Cue5f8C stretching modes of 1400–1600xa0cm −1 play an important role in the electron–phonon coupling in large acenes. The possible superconducting transition temperatures of the monoanions of benzene (C 6 H 6 ) and acenes are roughly estimated, on the basis of the hypothesis that vibronic interactions between the LUMO and intramolecular vibrations would play an essential role in the occurrence of superconductivity in these molecules.

The essential role of hydrogen atoms in the electron–phonon interactions in the monocation of cubic hydrocarbon cluster, (CH)8

Electron–phonon coupling in the monocations of cubic clusters such as cubane (CH)8 and octasilacubane (SiH)8 are studied. The total electron–phonon coupling constants for the monocations (lHOMO) are estimated and compared with those for the monoanions (lLUMO) in cubane and octasilacubane. The calculated lHOMO value for cubane (0.766 eV) is much larger than that for octasilacubane (0.327 eV). And the lHOMO values are larger than the lLUMO values both in cubane and octasilacubane. The frequencies (ωln,HOMO) of the vibrational modes which play an essential role in the electron–phonon interactions and the possible superconducting transition temperatures (Tcs) are estimated on the basis of the hypothesis that vibronic interactions between the highest occupied molecular orbitals (HOMO) and intramolecular vibrations would play an essential role in the occurrence of superconductivity in positively charged nanosized molecular systems. The phase pattern difference between the delocalized t2g HOMO in cubane and the ...

The relationships between the electronic structures and the normal and inverse isotope effects in the electron–phonon interactions in charged cubane

Electron–phonon coupling and possible normal and inverse isotope effects in the monoanion and cation of fully deuterated cubic cluster such as deutero-cubane (CD)8 are studied. The calculational results for charged deutero-cubane are compared with those for charged cubane. The calculated total electron–phonon coupling constants for the monoanion (lLUMO) and cation (lHOMO) of deutero-cubane are 0.631 and 0.777 eV, respectively. The lLUMO value increases much more significantly than the lHOMO value as a consequence of deuteration in cubane. Our calculational results show that inverse (normal) isotope effects as a consequence of full deuteration can be expected in the monoanion (monocation) of cubane. Significant phase patterns difference between the t1u lowest unoccupied molecular orbitals (LUMO) rather localized on carbon atoms and delocalized t2g highest occupied molecular orbitals (HOMO), and the larger displacements of carbon atoms in the Eg mode of 1072u2009cm−1u2009(ωD6) as a consequence of deuteration are th...

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.

Electron–intramolecular–vibration interactions in positively charged phenanthrene-edge-type hydrocarbons

Electron-phonon interactions in positively charged phenanthrene-edge-type hydrocarbons such as phenanthrene, chrysene, and picene are studied. The C-C stretching modes around 1500 cm(-1) and the low-frequency modes around 500 cm(-1) strongly couple to the highest occupied molecular orbitals (HOMO) in phenanthrene-edge-type hydrocarbons. The total electron-phonon coupling constants for the monocations (lHOMO) of 0.251, 0.135, and 0.149 eV for phenanthrene, chrysene, and picene, respectively, are estimated to be larger than those of 0.130, 0.107, and 0.094 eV for anthracene, tetracene, and pentacene, respectively. The phase patterns difference between the HOMO localized on carbon atoms which are located at the molecular edge in acene-edge-type hydrocarbons and the delocalized HOMO in phenanthrene-edge-type hydrocarbons is the main reason for the result. Strengths of orbital interactions between two neighboring carbon atoms in the HOMO become weaker with an increase in molecular size because the electron density on each carbon atom in the HOMO becomes smaller with an increase in molecular size in phenanthrene-edge-type hydrocarbons. On the other hand, the frontier orbitals of acene-edge-type hydrocarbons have somewhat nonbonding characters and thus cannot strongly couple to the totally symmetric vibrational modes compared with the frontier orbitals of phenanthrene-edge-type hydrocarbons. This is the reason why the lHOMO value for phenanthrene-edge-type hydrocarbons decreases with an increase in molecular size more significantly than that for acene-edge-type hydrocarbons, and the reason why the lHOMO value for polyphenanthrene with C2v geometry (0.033 eV) is estimated to be similar to that for polyacene (0.036 eV). The reorganization energies between the neutral molecules and the corresponding monocations for phenanthrene-edge-type hydrocarbons with large molecular size are estimated to be larger than those for acene-edge-type hydrocarbons with large molecular size.