Preparation of blue and green fluorescent dyes based on thioxanthone and phenothiazine derivatives and their thermal-stability, quantum yield properties

Eight dyes were synthesized to connect carbazole or naphthalimidinyl groups with a thioxanthone central ring utilizing an acetylene bond. In this series of fluorescent dyes, a nitrogen atom of both carbazole and naphthalimidyl rings were substituted by an n-butyl or phenyl group to use as a dye intermediate, then coupled to the central ring in the final step. Eight dyes prepared were identified using by 1H NMR, GC-Mass and elemental analyses. Main properties, such as the absorption maxima, emission maxima, molar extinction coefficient and thermal stabilities by TGA analysis of the fluorescent dyes prepared were examined. To optimize the structure of the dye molecules, calculations using a Density Functional Theory (DFT) and Time-Dependent DFT were performed for some dyes. In terms of absorption and emission maxima, six dyes from this series exhibited blue fluorescent emission those in the range of 443–457 nm, whereas two dyes substituted by either N-n-butyl-naphthalimide, or N-phenyl-naphthalimide group were red-shifted comparing to those of six dyes providing a green emission of 520 nm or 525 nm. The quantum yields for six dyes substituted by either N-n-Butyl-carbazole or N-phenyl-carbazole group were higher than those of analogous two dyes containing a naphthalimde group where all of six dyes exhibited 0.81–0.87 these were efficient compared to previous research.