Hydrazine → 9-Fluorenone hydrazone

Unsymmetrical charge transport materials can be prepared by using an unsymmetrical linking compound such as 6-dimethyl-1, 4-benzoquinone. Alternatively, unsymmetrical charge transport materials can be prepared by the following procedure. In the first step, a first 9-fluorenone or a derivative thereof reacts with an excess of hydrazine at 50-70° C. for 1-6 hours to produce a first 9-fluorenone hydrazone compound or a derivative thereof. Then, the first 9-fluorenone hydrazone compound can be isolated and purified. In a subsequent step, a second 9-fluorenone derivative reacts with an excess of hydrazine at 50-70° C. for 1-6 hours to produce a second 9-fluorenone hydrazone derivative. Then, the second 9-fluorenone hydrazone derivative can be isolated and purified. In another step, the first 9-fluorenone hydrazone derivative reacts with a linking compound having 2 aldehyde groups or ketone groups, such as OCH—CHO, a quinone derivative, or a diphenoquinone derivative, in a mole ratio of 1:1 to form an 9-fluorenone azine compound having one aldehyde or ketone group. In the next step, the second 9-fluorenone hydrazone derivative reacts with the 9-fluorenone azine compound in a mole ratio of 1:1 to form the desired product. The desired product can be isolated and purified by recrystalization or/and column chromatography. A person or ordinary skill in the art can reduce the amount of symmetrical by-products, and these symmetrical by-product compounds can be separated in the purification steps.