Five aryl- and amino-substituted dibenzo[b,e]phosphindolizine derivatives at the 10-position are synthesized and characterized. The HOMO and LUMO energy levels considerably change depending on the electronic nature of the substituents, especially for the electron-donating group.

Dibenzo[b,e]phosphindolizine oxides with five different aryl groups and a diphenylamino group at the 10-position are synthesized by the Suzuki–Miyaura cross-coupling reaction and the Buchwald–Hartwig amination reaction of 10-chlorodibenzo[b,e]phosphindolizine. The molecular structures and properties of the products are elucidated by X-ray crystallographic analysis, UV–vis spectroscopy, and electrochemical analysis. Dibenzo[b,e]phosphindolizines with p-(diphenylamino)phenyl and diphenylamino groups have smaller HOMO−LUMO gaps and higher HOMO energy levels than derivatives with methoxy and trifluoromethyl groups and without an amino group. The substituent effects are also investigated by theoretical calculations.