Aza-compounds derivatives such as carbazole and phenothiazine are intensively studied as potential components of organic electronics, particularly of OLEDs. The present paper deals with investigations of spectral properties of specific carbazole- and phenothiazine-containing low-molecular glass-forming compounds, i.e., 3-(9-carbazolyl)-9-ethylcarbazole, 3-(9-pheothiazinyl)-9-ethylphenothiazine, 3-(9-pheothiazinyl)-9-ethylcarbazole, and 3-(9-carbazolyl)-9-ethylphenothiazine in different aggregative states (solid samples and solutions) and at different temperatures (77 degrees K, 293 degrees K). The location of the first singlet and triplet energy levels of the investigated compounds has been estimated from the spectral data. The high probability of the intercombinatory transition to the triplet state for the solutions and solid samples of 3-(9-pheothiazinyl)-9-ethylphenothiazine, 3-(9-pheothiazinyl)-9-ethylcarbazole, and 3-(9-carbazolyl)-9-ethylphenothiazine has been stated.