Spin-orbital coupling and slow phonon effects enabled persistent photoluminescence in organic crystal under isomer doping

Abstract

When periodically packing the intramolecular donor-acceptor structures to form ferroelectric-like lattice identified by second harmonic generation, our CD49 molecular crystal shows long-wavelength persistent photoluminescence peaked at 542 nm with the lifetime of 0.43 s, in addition to the short-wavelength prompt photoluminescence peaked at 363 nm with the lifetime of 0.45 ns. Interestingly, the long-wavelength persistent photoluminescence demonstrates magnetic field effects, showing as crystalline intermolecular charge-transfer excitons with singlet spin characteristics formed within ferroelectric-like lattice based on internal minority/majority carrier-balancing mechanism activated by isomer doping effects towards increasing electron-hole pairing probability. Our photoinduced Raman spectroscopy reveals the unusual slow relaxation of photoexcited lattice vibrations, indicating slow phonon effects occurring in ferroelectric-like lattice. Here, we show that crystalline intermolecular charge-transfer excitons are interacted with ferroelectric-like lattice, leading to exciton-lattice coupling within periodically packed intramolecular donor-acceptor structures to evolve ultralong-lived crystalline light-emitting states through slow phonon effects in ferroelectric light-emitting organic crystal.

Necessary and sufficient condition for organic room-temperature phosphorescence from host-guest doped crystalline systems.

“…Thus, while isomer-free materials obtained from pure Cz did not exhibit any afterglow, in contrast, crystals of Cz-based emitters synthesized from commercial Cz as well as isomer-free crystalline systems doped with controlled amounts of their corresponding isomeric impurities exhibited obvious RTP 31,[33][34][35] . Therefore, this new context brings RTP from single-component Cz-based systems into question, and leads to discuss them as the multi-component RTP systems (host-guest doped systems).…”

Structurally Resemblant Dopants Enhance Organic Room‐Temperature Phosphorescence

“…Recently, the research community has paid increasing attention to the existence and identification of trace dopants and their impacts on respective organic RTP systems. [19][20][21][23][24][25][26][27][28] Noted as early as 1930s, a trace amount of impurity associated with the raw materials used for RTP compound synthesis could be a naturally occurring dopant in originating RTP. [2,23,29,30] However, such impurity or dopant-induced organic phosphors have rarely been studied and researched in the past due to difficulties in isolating and identifying the associated dopants.…”

Necessary and Sufficient Condition for Organic Room‐Temperature Phosphorescence from Host–Guest Doped Crystalline Systems

“…Thus, while isomer-free materials obtained from pure Cz did not exhibit any afterglow, in contrast, crystals of Cz-based emitters synthesized from commercial Cz, as well as isomer-free crystalline systems doped with controlled amounts of their corresponding isomeric impurities exhibited obvious RTP. [30,[32][33][34] Therefore, this new context brings RTP from single-component Cz-based systems into question, and leads to discussing them as multi-component RTP systems (host-guest doped systems). More generally, it is obvious that establishing new emitters rational design guidelines, as well as structure-properties relationships still remains highly challenging, most notably in the case of purely organic host-guest-doped RTP systems.…”