Tunable Green Emitting Novel Phosphazene Compounds via Azide–Alkyne Cycloaddition: Evaluation of Photodiode Performance, Synthesis, and Photophysical Characterization

This study aims to develop new photodiode materials containing functional chalcone derivatives by combining the electronic properties of the cyclotriphosphazene ring with click chemistry. Azide-terminated chalcones were subjected to a click reaction with an alkyne-functionalized dispirocylotriphosphazene (Bif-PA) to afford the Bif-PA-Click-Chal 1-4 compounds, whose structural characterizations were confirmed by FT-IR, NMR, and MALDI-TOF MS analyses. Photophysical properties were investigated using UV-vis and fluorescence spectroscopy, and the Bif-PA-Click-Chal 1 compound exhibited a quantum yield of 0.32 and high emission intensity. For the Bif-PA-Click-Chal 1 molecule, absorption parameters were calculated using CPCM/6-31G(d,p) and TD-DFT/CAM-B3LYP methods (in THF), revealing a theoretical bandgap of 3.53 eV, whereas experimental UV-vis measurements indicated a bandgap of 2.69 eV. Electrical measurements were performed to investigate the <i>I</i>-<i>V</i> characteristics of the new types of diodes fabricated using the Bif-PA-Click-Chal 1-4 compounds. Among these, Bif-PA-Click-Chal 1 and 2 demonstrated diode performance. Comparison of their diode properties showed that both compounds behaved as semiconductors exhibiting diode characteristics. Bif-PA-Click-Chal 2 stood out with a high rectification ratio (RR = 523.64), low saturation current (<i>I</i>₀ = 1.27 × 10^-8 A), a better ideality factor (<i>n</i> = 2.51), and high barrier height (ϕ_b = 0.76 eV). However, measurements performed under various light intensities indicated that it did not exhibit photodiode behavior. In contrast, Bif-PA-Click-Chal 1, despite displaying a lower rectification ratio (RR = 80.45), higher saturation current (<i>I</i>₀ = 2.38 × 10^-8 A), and an ideality factor of <i>n</i> = 2.73, demonstrated photodiode behavior under different light intensities. These findings confirm that both compounds exhibit diode characteristics; however, the photodiode behavior of Bif-PA-Click-Chal 1 and its superior <i>I</i>-<i>V</i> characterization reveal that it possesses enhanced electronic and photoconductive properties compared to its counterparts.