Efforts have been increased to create efficient photodiodes using a variety of interface layers such as organics, insulators, polymers, and metal oxides. Therefore, in this study, novel 4,5-diazafluorene ligands and their ruthenium (II) complexes were designed, synthesized, and elucidated by using 1H NMR, FT-IR, UV-Vis, and mass spectroscopic (LC–MS) methods. The NMR, FT-IR, UV-Vis, and LCMS spectrometer results explained and confirmed the structure of the 4,5-diazafluorene ligands and their ruthenium (II) complexes. The obtained 4,5-diazafluorene ligands and their ruthenium (II) complexes were used as interfacial layer for Schottky type photodiode and characterized by I−V measurements for various light power intensities. Various diode parameters such as rectification ratio, series resistance, and barrier height as well as ideality factor values were extracted and discussed in details. The results revealed that the fabricated Schottky type photodiodes with 4,5-diazafluorene ligands and their ruthenium (II) complex interlayers can be employed and improved for optoelectronic applications.