Experimental Studies on Extremely Slow Phonon Dynamics and Circularly Polarized Excitonic Emission in Organic Multi-functional Materials

Understanding and controlling exciton behavior in molecular and hybrid crystalline systems is pivotal to advancing next-generation optoelectronic technologies. This dissertation investigates exciton dynamics, spin–orbit coupling (SOC), and circularly polarized luminescence (CPL) across four interrelated material systems: donor–acceptor (D–A) type organic crystals, chiral metal–organic frameworks (MOFs), luminescent radicals, and chiral perovskite crystals. Chapter 1 introduces these materials along with the concepts of extremely slow phonon dynamics and circularly polarized excitonic emission.

Chapter 2 explores the role of phonon dynamics in polar organic crystals with D–A configurations. Through time-resolved photoluminescence and structural characterization, we discovered that ultra-slow phonon interactions prolong excited-state lifetimes via a triplet-based charge transfer mechanism. This manifests as super-delayed fluorescence, revealing a novel phonon-assisted luminescence pathway.

Chapter 3 focuses on spin–orbit coupling effects in chiral MOFs. Structural chirality induces Rashba-type band formation and non-degenerate spin states. By correlating SOC-driven optical transitions with luminescence lifetimes, we demonstrate that chiral MOFs enable spin-selective emission, highlighting their potential for chiral optical devices.

Chapter 4 investigates spin-dependent behavior of circularly polarized excitons in organic radical-doped crystals. The doublet states in radicals circumvent traditional spin statistics limitations to enable excited-state luminescence. Significant CPL signals were observed experimentally, with magnetic field application enhancing both intensity and degree of polarization. This magnetic enhancement verifies synergistic interactions between doublet states, SOC, and spin-mixing processes.

Chapter 5 examines spin–orbit coupling ordering in chiral perovskite crystals. Through CPL and magneto-optical spectroscopy at low temperatures, we observed magnetic field-enhanced circularly polarized excitonic emissions. The combination of chirality-induced Rashba bands and helically arranged SOC enables magnetic field modulation of excited-state behavior, providing direct evidence of excitonic spin ordering.

Chapter 6 provides a comprehensive summary of this dissertation and discusses the implications from the perspective of future applications. It focuses on overcoming traditional limitations in light emission using open-shell radical systems, chiral material design, and spin-polarization mechanisms. The experimental findings presented in this work—including the suppression of non-radiative losses, regulation of electron–phonon coupling, and realization of efficient circularly polarized light emission via chiral architectures—offer a solid foundation for the development of next-generation spintronic optoelectronic devices and quantum information technologies.