The triplet state of 4,4',4 ''-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA) and the dynamics of the singlet and the triplet states were examined to understand the confinement effect of m-MTDATA as host materials for phosphorescent organic light-emitting diodes. The time-resolved photoluminescence spectra revealed phosphorescence at approximately 480 nm (2.58 eV). The time constant of the T-1 state was 1.2 mu s. The dynamics of delayed fluorescence was closely related to that of phosphorescence. The triplet energy of a green phosphorescent sensitizer was well-confined in the m-MTDATA host, which suggests the application of m-MTDATA as possible host materials. (C) 2010 Elsevier B.V. All rights reserved.