Chapter 5
Suppression of Internal Conversions
from Pseudo-Degenerate Excited
Electronic States
Wataru Ota and Tohru Sato
Abstract We describe the relationship between the rate constant of internal conversion and vibronic coupling constant (VCC) based on the crude-adiabatic approximation. Vibronic coupling density (VCD) is introduced to clarify the origin of
vibronic couplings from the local picture. The control of vibronic couplings from
pseudo-degenerate excited electronic states gives the suppression of internal conversions. We discuss the fluorescence via higher triplets (FvHT) mechanism observed
in the organic light-emitting diodes (OLEDs) of 1,4-bis(10-phenylanthracene-9yl)benzene (BD1) used as a fluorescent dopant and the aggregation-induced enhanced
emission (AIEE) of 1,2-bis(pyridylphenyl)ethene (CNPPE).
Keywords Vibronic coupling density · Pseudo-degeneracy · Internal conversion ·
Fluorescence via higher triplets mechanism · Organic light-emitting diodes ·
Aggregation-induced enhanced emission
5.1 Introduction
Vibronic couplings, the interactions between vibrational and electronic motions,
induce internal conversions between electronic states. The suppression of internal
conversions is achieved by the control of vibronic couplings, which can provide a
design principle for novel light-emitting molecules. Vibronic coupling density (VCD)
defined by the spatial density distribution of a vibronic coupling constant (VCC) is
developed to elucidate the origin of vibronic couplings from the local picture [1,
2]. In this chapter, using the concept of VCD, we show that pseudo-degeneracy of
W. Ota · T. Sato (B)
Fukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8103, Japan
e-mail: tsato@scl.kyoto-u.ac.jp
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University,
Nishikyo-ku, Kyoto 615-8510, Japan
T. Sato
Unit of Elements Strategy Initiative for Catalysts & Batteries, Kyoto University, Nishikyo-ku,
Kyoto 615-8510, Japan
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_5
79
Suppression of Internal Conversions
from Pseudo-Degenerate Excited
Electronic States
Wataru Ota and Tohru Sato
Abstract We describe the relationship between the rate constant of internal conversion and vibronic coupling constant (VCC) based on the crude-adiabatic approximation. Vibronic coupling density (VCD) is introduced to clarify the origin of
vibronic couplings from the local picture. The control of vibronic couplings from
pseudo-degenerate excited electronic states gives the suppression of internal conversions. We discuss the fluorescence via higher triplets (FvHT) mechanism observed
in the organic light-emitting diodes (OLEDs) of 1,4-bis(10-phenylanthracene-9yl)benzene (BD1) used as a fluorescent dopant and the aggregation-induced enhanced
emission (AIEE) of 1,2-bis(pyridylphenyl)ethene (CNPPE).
Keywords Vibronic coupling density · Pseudo-degeneracy · Internal conversion ·
Fluorescence via higher triplets mechanism · Organic light-emitting diodes ·
Aggregation-induced enhanced emission
5.1 Introduction
Vibronic couplings, the interactions between vibrational and electronic motions,
induce internal conversions between electronic states. The suppression of internal
conversions is achieved by the control of vibronic couplings, which can provide a
design principle for novel light-emitting molecules. Vibronic coupling density (VCD)
defined by the spatial density distribution of a vibronic coupling constant (VCC) is
developed to elucidate the origin of vibronic couplings from the local picture [1,
2]. In this chapter, using the concept of VCD, we show that pseudo-degeneracy of
W. Ota · T. Sato (B)
Fukui Institute for Fundamental Chemistry, Kyoto University, Sakyo-ku, Kyoto 606-8103, Japan
e-mail: tsato@scl.kyoto-u.ac.jp
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University,
Nishikyo-ku, Kyoto 615-8510, Japan
T. Sato
Unit of Elements Strategy Initiative for Catalysts & Batteries, Kyoto University, Nishikyo-ku,
Kyoto 615-8510, Japan
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_5
79