Conjugated diazochalcone-phosphazene hybrids: Design, synthesis, and substituent effects on optical and electrical properties

Abstract

Phosphazene derivatives have gained an important place in functional materials chemistry thanks to their versatile structural regularity and chemical stability, while diazochalcone structures are compounds with remarkable potential in organic electronic and photonic applications as photosensitive conjugated systems. In this study, two new hybrid structures, CRG-4F and CRG-4DMA, functionalized with a dual diazochalcone group on the cyclotriphosphazene core, obtained by combining these two important structures, were synthesized, characterized, and their optoelectronic properties were studied in detail. In the optical investigations by UV-Vis spectroscopy, the maximum absorption wavelength of CRG-4F was determined as similar to 350 nm, and that of CRG-4DMA as similar to 405 nm due to the broadening of the conjugation. The direct band gaps calculated by the Tauc method are 2.95 eV and 2.62 eV, respectively, revealing the band gap narrowing effect of the electron-donating dimethylamino group. Both compounds were tested in a diode configuration in Al/organic material/p-Si configuration and exhibited forward conduction and reverse low current characteristics. CRG-4F exhibited superior diode behavior with a higher rectification ratio, while CRG-4DMA stood out as a photosensitive compound by generating more pronounced photoresponse with increasing light intensity under reverse voltage. The results show that the combination of phosphazene core with diazochalcone offers an effective design strategy to develop a new generation of organic-inorganic semiconductors with tunable band gap, solvent-sensitive optical properties, and functional diode performance depending on the nature of the substituent. The findings highlight the potential of these materials in opto-electronic devices, especially in visible region sensitive photodetectors, organic light emitting components, and sensor technologies.