共役系高分子鎖における増幅自発発光の電荷蓄積とその動的フォノンスペクトル

Charge Accumulation of Amplified Spontaneous Emission in a Conjugated Polymer Chain and Its Dynamical Phonon Spectra.

• Zhe Lin
• Jiahao Chen
• Yusong Zhang
• Jianguo Shen
• Sheng Li
• Thomas F George

抄録

本論文では、非断熱的な分子動力学と電子遷移を組み合わせた詳細な光励起ダイナミクスにより、共役系高分子における自発的な電気分極を伴う増幅自発発光(ASE)の発生を示した。超高速光励起の精巧な分子動力学過程は以下のように記述できる。連続的な外部光励起（レーザー70μJ/cm）は、瞬時に4レベルの電子構造を出現させるだけでなく、ASEの母集団反転をも引き起こす。同時に、共役ポリマーのフォノンスペクトルが変化し、両端に5つの局所的な赤外格子振動モードが形成され、系の元々の対称性が破られ、外部電場なしでポリマー鎖の両端に電荷が蓄積される。この新しい現象は、固体共役系高分子の超高速効果をもたらす刺激発光の進化に格子振動がどのような役割を果たしているかを説明する全く新しい道筋を与えるものである。

In this article, the detailed photoexcitation dynamics which combines nonadiabatic molecular dynamics with electronic transitions shows the occurrence of amplified spontaneous emission (ASE) in conjugated polymers, accompanied by spontaneous electric polarization. The elaborate molecular dynamic process of ultrafast photoexcitation can be described as follows: Continuous external optical pumping (laser of 70 µJ/cm) not only triggers the appearance of an instantaneous four-level electronic structure but causes population inversion for ASE as well. At the same time, the phonon spectrum of the conjugated polymer changes, and five local infrared lattice vibrational modes form at the two ends, which break the original symmetry in the system and leads to charge accumulation at the ends of the polymer chain without an external electric field. This novel phenomenon gives a brand-new avenue to explain how the lattice vibrations play a role in the evolution of the stimulated emission, which leads to an ultrafast effect in solid conjugated polymers.