Carboline, also known as diazepine, is a heterocyclic compound in which a pyridine ring and an indole pyrrole ring are fused. In the carboline structure, it is divided into α-carboline, β-carboline and γ-carboline according to the position of the pyridine nitrogen atom. The structure of carbolines is similar to that of fluorene compounds, and it has the advantages of high thermal stability, high luminous efficiency, and variable chemical structure. From the chemical structure, carboline replaces two carbon atoms on fluorene with two nitrogen atoms. The substitution of nitrogen atoms makes carbolines have strong electron affinity. The use of carboline derivatives as semiconductor materials can enhance the electron affinity under the spectrum remains unchanged, which is beneficial to the injection of electrons and improves the efficiency of semiconductor devices. In addition, in terms of chemical structure modification, imine connecting two aromatic rings has high activity, is easy to be chemically modified, and can form a derivative with its unique activity and performance. Therefore, carboline-based materials have applications in many fields such as organic electroluminescence and sensitized solar cells.
Figure 1. Structure of β-carboline
- Electron transport materials: In the field of organic light-emitting diodes, in order to obtain higher luminous efficiency and longer luminous lifetime, it is necessary to use a material that can effectively recombine holes and electrons as a transport layer. Carboline materials have strong electron affinity due to the presence of nitrogen atoms. This enables the carboline material to be used as both an electron transport material and a hole blocking layer material, which is beneficial to improve the luminous efficiency of the device. Carboline materials can also be used as excellent electron transport materials to prepare fuel-sensitized solar cells.
- Luminous material: Carboline materialsre a kind of good metal ligands, which can form complexes with europium, iridium and ruthenium. Such complexes have excellent luminescent properties and are often used as electrophosphorescent materials in light-emitting devices. Carboline complex phosphorescent materials have high internal quantum efficiency, which greatly improves the luminous efficiency of organic electroluminescent devices.
- Wei-Jie Li, Bin Liu, Yan Qian, Ling-Hai Xie, Jing Wang, Sheng-Biao Li, Wei Huang. Synthesis and characterization of diazafluorene-based oligofluorenes and polyfluorene [J]. Polym. Chem., 2013, 4, 1796-1802.