Correlated semiempirical and ab initio quantum-chemical methods are applied to the description of the lowest-lying triplet excited state, T-1, in conjugated molecules used as hosts in phosphorescent light emitting diodes. Density functional theory is found to lead to the best agreement between measured and calculated excitation energies in a set of reference molecules. The trade-off between the barrier for charge injection and the singlet-triplet S-0-->T-1 energy spacing is discussed in the context of the design of molecular hosts for blue triplet guest emitters. (C) 2004 Elsevier B.V. All rights reserved.