Halogen-bonded charge-transfer co-crystal scintillators for high-resolution X-ray imaging.

The development of high-quality organic scintillators encounters challenges primarily associated with the weak X-ray absorption ability resulting from the presence of low atomic number elements. An effective strategy involves the incorporation of halogen-containing molecules into the system through co-crystal engineering. Herein, we synthesized a highly fluorescent dye, 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole (Py2TTz), with a fluorescence quantum yield of 12.09%. Subsequently, Py2TTz was co-crystallized with 1,4-diiodotetrafluorobenzene (I2F4B) and 1,3,5-trifluoro-2,4,6-triiodobenzene (I3F3B) obtaining Py2TTz-I2F4 and Py2TTz-I3F3. Among them, Py2TTz-I2F4 exhibited exceptional scintillation properties, including an ultrafast decay time (1.426 ns), a significant radiation luminescence intensity (146% higher than Bi3Ge4O12), and a low detection limit (70.49 nGy s-1), equivalent to 1/78th of the detection limit for medical applications (5.5 µGy s-1). This outstanding scintillation performance can be attributed to the formation of halogen-bonding between I2F4B and Py2TTz. Theoretical calculations and single-crystal structures demonstrate the formation of halogen-bond-induced rather than π-π-induced charge-transfer cocrystals, which not only enhances the X-ray absorption ability and material conductivity under X-ray exposure, but also constrains molecular vibration and rotation, and thereby reducing non-radiative transition rate and sharply increasing its fluorescence quantum yields. Based on this, the flexible X-ray film prepared based on Py2TTz-I2F4 achieved an ultrahigh spatial resolution of 26.8 lp per mm, underscoring the superiority of this strategy in developing high-performance organic scintillators.

Correction: Halogen-bonded charge-transfer co-crystal scintillators for high-resolution X-ray imaging.

[This corrects the article DOI: 10.1039/D4SC00735B.].

Naphthalenediimide/Iodobismuthate Hybrid Heterostructures: Water Resistance and Long-Lived Charge-Separated States.

Organic-inorganic hybrid iodobismuthate perovskites have become promising semiconductive materials for their environmentally friendly and light-harvesting characteristics. However, their low-dimensional bismuth-iodide skeletons result in poor charge-separation efficiency, limiting their application in optoelectronic devices. To address this issue, the donor-acceptor (D-A) heterostructures have been introduced to the iodobismuthate hybrid materials by incorporating an electron-deficient N,N'-bis(4-aminoethyl)-1,4,5,8-naphthalene diimide (NDIEA) as the electron acceptor and organic counterpart. Five naphthalenediimide/iodobismuthate hybrid heterostructures, named (H2NDIEA)1.5·Bi2I9·3DMF (1), H2NDIEA·[Bi2I8(DMF)2]·2DMF (2), (H2NDIEA)2·Bi4I16·2H2O·4MeOH (3), (H2NDIEA)2·Bi4I16·8H2O (4), and [(H2NDIEA)2·Bi6I22]n·4nH2O (5) (DMF = N,N-dimethylformamide), were synthesized. Their crystal structures, water stabilities, charge-separated behaviors, and electrical properties have been studied through experimental and computational investigations. The results revealed that hybrids 3-5 exhibited high water resistance attributed to their tightly packed structures and robust H-bonds between solvent molecules and organic-inorganic supramolecular frameworks. Density functional theory calculations confirmed characteristic type-IIa band alignments of all the five hybrids, facilitating to the photoinduced charge separation. Moreover, the closer contact caused by the strong anion-π interactions between electron donors and acceptors in hybrid 5 leads to the long-lived charge-separated states and improved electrical properties compared to the other hybrids.

Three Semiconductive 1D Naphthalene Diimide/Iodoplumbate Perovskites with High Moisture Tolerance and Long-Lived Charge Separation States.

Low-dimensional inorganic-organic hybrid perovskites with high moisture tolerance and long-lived charge separation states have captured significant attention in the field of optoelectronic devices. To further achieve the relationship between crystal structures and stability, as well as charge separation behaviors, three one-dimensional hybrid perovskites containing electron-deficient naphthalene diimide ammonium (NDIEA) and electron-rich iodoplumbate chains, [(H2NDIEA)Pb2I6]·2DMF (1), [(H2NDIEA)2Pb5I14·(DMF)2]·4DMF (2), and [(HNDIEA)2Pb2I6]·3H2O (3), were synthesized. Crystal structure determinations revealed various synthesis conditions leading to different stacking modes, especially the inorganic lead iodide fraction, which resulted in different water resistances and charge-separated behaviors. The comprehensive analysis found that strong intermolecular interactions (anion-π interactions and π-π interactions), and matching energy levels between protonated NDIEA and iodoplumbate chains, can facilitate the generation of long-lived charge separation states and extraordinary moisture stability, even in the water environment. In addition, the conductivity behavior of 3 was also explored in detail.