Ferrocene−Phenothiazine Conjugated Molecules: Synthesis, Structural Characterization, Electronic Properties, and DFT-TDDFT Computational Study

Two novel Fc−MPT conjugated compounds, 3-(ferrocenylethynyl)-10-methylphenothiazine ( 1 ) and 3,7-bis(ferrocenylethynyl)-10-methylphenothiazine ( 2 ), have been synthesized by Sonogashira cross-coupling reactions. Single-crystal X-ray diffraction shows that 2 displays better coplanarity between the Fc and MPT subunits. The crystal packing reveals that 1 stacks in the same direction between the neighboring molecules by the S···H−C (of the Fc moiety) hydrogen bonds, while 2 stacks in an inverse fashion between the adjacent molecules, not only by the S···H−C (of the MPT moiety) hydrogen bonds but also by π···π interactions. Both complexes show MLCT, ICT, and π → π* transitions in the UV−visible range in solution, and 2 has a tremendous bathochromic shift and shows a higher oscillator strength of the absorption, which has been verified by TDDFT theoretical calculations. DFT calculations explain the electrochemistry of the two complexes and show that the larger conjugative effect in 2 leads to the smaller HOMO−LUMO gap ( E g ). The differences between 1 and 2 indicate that the structural and conjugative effects have great influence on the electronic properties of the molecules.