Spectroelectrochemical study on a new absorption band of radical cations of
4,4’-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (α-NPD) as an
electron-donor hole-transporting material used in organic electronics is
reported in this work. UV-visible spectroscopic and cyclic voltammetric
properties for α-NPD in solution are also examined. We find that the results
are attributed to quenching process for blue fluorescence from α-NPD by
excess α-NPD+ radical cations accumulated in the emission region
in the organic light-emitting devices related to a relatively large overlap
between the fluorescence spectrum of α-NPD and the absorption spectrum of
α-NPD+ radical cations. The band gap energy for α-NPD is
calculated from the UV-visible spectroscopic data.