Biphenyl compounds are an important class of chemical intermediates, which are widely used in the fields of drugs, dyes, organic conductors, semiconductors and liquid crystal materials. There are many synthetic methods for biphenyl compounds, such as electrochemical synthesis, intramolecular coupling, organometallic coupling, etc. Biphenyl compounds are mainly composed of benzene rings connected by carbon-carbon single bonds, and compounds such as biphenyl and terphenyl can be obtained by expansion. Extending the π-conjugated system with the benzene ring as the center or introducing conjugated groups can expand the conjugation plane and increase the intermolecular interaction and stability. Among semiconductor materials, biphenyl compounds have rigid conjugated cyclic structures and excellent stability, making them widely used in organic light-emitting devices and organic transistors.
Figure 1. Chemical structure of biphenyl
- Hole blocking material: In organic light emitting diode (OLED) devices, the hole transport rate of the hole transport material is much higher than the electron mobility of the electron transport material. In order to make electrons and holes recombine in the light-emitting layer to form excitons and emit light, hole blocking materials are often used to effectively prevent holes from reaching the electron transport layer. Biphenyl compounds have a lower highest occupied molecular orbital (HOMO) energy level, which can effectively prevent the transport of holes, so that holes and electrons form exciton recombination in the light-emitting layer rather than in the electron transport layer.
- Organic Field Effect Transistor (OFET): The performance of OFETs mainly depends on the mobility of organics. The mobility of organic matter is affected by the strength of the π-π bond between adjacent molecules and the order of the molecular arrangement. Biphenyl compounds have small molecular spacing and strong π-π bond force, making them ideal OFET semiconductor materials. By further modifying the end groups of the biphenyl compounds, a crystalline film can also be obtained by vapor deposition, and a thin-film semiconductor material can be obtained.
- Rudranarayan Khatua, Smruti Ranjan Sahoo, Sagar Sharma, Sridhar Sahu. Anisotropic charge transport and optoelectronic properties of wide band gap organic semiconductors based on biphenyl derivatives: A computational study [J]. Synth. Met., 2020, 267, 116474.