Two methylated thienocarbazoles and two of their synthetic nitro-precursors have been examined by absorption, luminescence, laser flash photolysis and photoacoustic techniques. Their spectroscopic and photophysical characterization involves fluorescence spectra, fluorescence quantum yields and lifetimes, and phosphorescence spectra and phosphorescence lifetimes for all the compounds. Triplet–singlet difference absorption spectra, triplet molar absorption coefficients, triplet lifetimes, intersystem crossing S₁ ∼∼→ T₁ and singlet molecular oxygen yields were obtained for the thienocarbazoles. In the case of the thienocarbazoles it was found that the lowest-lying singlet and triplet excited states, S₁ and T₁, are of π,π* origin, whereas for their precursors S₁ is n,π*, and T₁ is π,π*. In both thienocarbazoles it appears that the thianaphthene ring dictates the S₁ ∼∼→ T₁ yield, albeit there is less predominance of that ring in the triplet state of the linear thienocarbazole, which leads to a decrease in the observed ϕ_T value.