Photophysics and Spin‐Physics Studies on Persistent Upconversion Luminescence from Nonlinearly Polarizable Ferroelectric‐Like Lattice Prepared by Orderly Packing Donor–Acceptor Structures under Multiphoton Excitation

Abstract

The ultralong‐lived upconversion luminescence with the lifetime of 0.48 s in a broad spectral range (530–650 nm) is observed in CD49 (9‐(3‐(5‐bromopyridin‐3‐yl)prop‐2‐yn‐1‐yl)‐9H‐carbazole) crystal designed with donor–acceptor (carbazole–pyridine) structures under infrared excitation, simultaneously accompanied with second harmonic generation (SHG). This phenomenon indicates orderly packing donor–acceptor structures form a nonlinearly polarizable ferroelectric‐like lattice with ultralong‐lived light‐emitting states, leading to much prolonged nonlinear optical behaviors. The persistent upconversion luminescence together with SHG is largely reduced when lowering crystallinity. This implies that nonlinearly polarizable ferroelectric‐like lattice provides the necessary condition to generate persistent upconversion luminescence. Evidently, persistent upconversion luminescence becomes completely lacking when only using ultralong‐lived light‐emitting states without nonlinearly polarizable ferroelectric‐like lattice, exampled by 4‐(dimethylamino)benzonitrile dispersed in polyvinyl alcohol matrix. Magneto‐photoluminescence shows that persistent upconversion luminescence is essentially a super‐delayed fluorescence from crystalline intermolecular charge‐transfer excitons formed in the nonlinearly polarizable ferroelectric‐like lattice. Magnetodielectrics indicate crystalline intermolecular charge‐transfer excitons are coupled with nonlinearly polarizable ferroelectric‐like lattice, leading to prolonged nonlinear optical behaviors shown as persistent upconversion luminescence through super delayed fluorescence. Therefore, crystalline intermolecular charge‐transfer excitons formed in nonlinearly polarizable ferroelectric‐like lattice provide an interesting platform to generate prolonged nonlinear optical behaviors toward developing persistent upconversion luminescence under multiphoton excitation.

Color‐Tunable Dual‐Mode Organic Afterglow for White‐Light Emission and Information Encryption Based on Carbazole Doping

“…The structures of molecules used in this study are depicted in Figure 1a, with Cz serving as the host molecule, and Bd, BCz, and DBCz as the guest molecules. Detailed synthetic methods can be found in the Supporting Information, and the right structures of the products were confirmed with 1 H NMR and 13 C NMR spectra (Figure S1-S8). Their purity was confirmed by high performance liquid chromatography spectra as shown in Figure S9.…”

“…Delayed spectra of Bd/Cz, BCz/Cz and DBCz/Cz host–guest systems with different doping concentrations were also measured to investigate their afterglow properties (Figure 2d–f, Figure S12). All the host–guest systems exhibited two afterglow bands in the range of 390–450 nm and 540–650 nm with their emission intensity depending highly on doping concentrations [11b,12c, 13] . The first emission band of delayed spectra was delayed fluorescence, which overlapped with the corresponding steady state emission.…”