Electron-Phonon Interactions in Novel Nanoelectronics

✍ Scribed by Takashi Kato

• Publisher: Nova Science Publishers Inc
• Year: 2009
• Tongue: English
• Leaves: 97
• Category: Library

✦ Synopsis

In this book, the electron-phonon interactions in the charged molecular systems such as polyacenes, polyfluoroacenes, B, N-substituted polyacenes, and polycyanodienes are discussed. They estimated the electron-phonon coupling constants and the frequencies of the vibronic active modes playing an essential role in the electron-phonon interactions in order to discuss how CH-CF, CC-BN, and CC-CN substitutions are closely related to the essential characteristics of the electron-phonon interactions in these molecules by comparing the calculated results for charged polyacenes with those for charged B, N-substituted polyacenes and polycyanodienes, respectively. The C-C stretching modes around 1500 cm-1strongly couple to the highest occupied molecular orbitals (HOMO), and the lowest frequency modes and the C-C stretching modes around 1500 cm-1 strongly couple to the lowest unoccupied molecular orbitals (LUMO) in polyacenes. The C-C stretching modes around 1500 cm -1strongly couple to the HOMO and LUMO in polyfluoroacenes. The B-N stretching modes around 1500 cm -1 strongly couple to the HOMO and LUMO in B, N-substituted polyacenes. The C-C and C-N stretching modes around 1500 cm-1 strongly couple to the HOMO and LUMO in polycyanodienes. The total electron-phonon coupling constants for the mono cations and mono anions decrease with an increase in molecular size in polyacenes, polyfluoroacenes, B, N-substituted polyacenes, and polycyanodienes. In general, we can expect that mono cations and mono anions, in which number of carriers per atom is larger, affords larger value. The CH-CF, CC-BN, and CC-CN atomic substitutions are effective way to seek for larger values, and the CH-CF and CC-CN atomic substitutions are effective way to seek for larger values in polyacenes. The logarithmically averaged phonon frequencies which measure the frequencies of the vibronic active modes playing an essential role in the electron-phonon interactions for the mono cations and mono anions in polyacenes, polyfluoroacenes, B, N-substituted polyacenes, and polycyanodienes are investigated. The values decrease with an increase in molecular size in polyacenes, polyfluoroacenes, and polycyanodienes, and the values decrease with an increase in molecular size in polyacenes, polyfluoroacenes, B, N-substituted polyacenes, and polycyanodienes. The authors can expect that in the hydrocarbon molecular systems, the values would basically decrease by substituting hydrogen atoms by heavier atoms. This can be understood from the fact that the frequencies of all vibronic active modes in polyacenes downshift by H-F substitution. However, considering that the value for the LUMO rather localized on carbon atoms in large sized polyfluoroacenes becomes larger by H-F substitution, the authors can expect that the value for a molecular orbital localized on carbon atoms has a possibility to increase by substituting hydrogen atoms by heavier atoms if the phase patterns of the molecular orbital do not significantly change by such atomic substitution. Therefore, the detailed properties of the vibrational modes and the electronic structures as well as the molecular weights are closely related to the frequencies of the vibronic active modes playing an important role in the electron-phonon interactions in the mono anions of polyfluoroacenes.

✦ Table of Contents

ELECTRON-PHONON INTERACTIONS IN NOVEL NANOELECTRONICS......Page 3
CONTENTS......Page 7
PREFACE......Page 9
INTRODUCTION......Page 11
THEORETICAL BACKGROUND......Page 15
A. Vibronic Interactions between the Twofold Degenerate Frontier Orbitals and the E2g Vibrational Modes In Benzene......Page 17
B. Vibronic Interactions between the Twofold Degenerate Frontier Orbitals and the A1g Vibrational Modes in Benzene......Page 20
C. Vibronic Interactions between the Nondegenerate Frontier Orbitals and the Ag Vibrational Modes in Polyacenes......Page 21
D. Vibronic Interactions in Polyfluoroacenes, B, N-Substituted Polyacenes, and Polycyanodienes......Page 23
ELECTRON–PHONON COUPLING CONSTANTS FOR THE CHARGED ELECTRONIC STATES OF POLYACENES, POLYFLUOROACENES, B, N-SUBSTITUTED POLYACENES, AND POLYCYANODIENES......Page 25
A. Twofold Degenerate Electronic States of The Monocations of Monoanions of Benzene, Hexafluorobenzene, and Borazine......Page 28
B. Nondegenerate Electronic Systems of Polyacenes, Polyfluoroacenes, B, N-Substituted Polyacenes, and Polycyanodienes......Page 30
A. Benzene and Polyacenes......Page 31
B. Polyfluoroacenes......Page 33
C. B, N-Substituted Polyacenes......Page 35
D. Polycyanodienes......Page 36
A. The Monocations and Monoanions of Benzene and Polyacenes......Page 37
1. Monocations......Page 41
2. Monoanions......Page 44
1. Monocations......Page 49
2. Monoanions......Page 51
1. Monocations......Page 53
2. Monoanions......Page 54
E. Summary......Page 57
1. Monocations......Page 59
2. Monoanions......Page 61
B. B, N-Substituted Polyacenes......Page 64
1. Monocations......Page 67
2. Monoanions......Page 68
D. Summary......Page 70
THE LOGARITHMICALLY AVERAGED PHONON FREQUENCIES......Page 73
1. Monocations......Page 74
2. Monoanions......Page 75
B. B, N-Substituted Polyacenes......Page 77
C. Polycyanodienes......Page 79
D. Summary......Page 80
CONCLUDING REMARKS......Page 83
ACKNOWLEDGMENT......Page 87
REFERENCES......Page 89
INDEX......Page 95