Luminescent properties of newly synthesized thioxanthone-polypyridyl derivatives and their metal-organic complexes

Abstract

Thioxanthones (TXs) are not only important photoinitiators for free radical polymerization but also efficient light-harvesting units for organic light emitting diodes. Here, we reported synthesis and photophysical properties of new TXs with 2,2′-bipyridyl (BPy) and 2,2':6′,2″-terpyridyl (TPy) substituents, TXOBPy and TXOTPy, as well as those of their complexes with some transition metal ion (Zn2+, Fe2+, Ni2+, Eu3+ and Tb3+) solution in diverse solvents and solid powders. Absorption spectra revealed mainly two groups of bands at approximately 250–290 and 366 nm, attributed to the π–π* and n–π* electron transfer of the TXs. A broad luminescent emission was recorded and centered at approximately 422 nm for these TXs and their metal complexes, its relative intensity was solvent and concentration dependent. Further, it was observed that this emission band red shifted to approximately 470 nm in their solid powders. For the TXs and their Zn/Fe/Ni-complexes in the methanol solutions, the quantum efficiency (QE) of TX rings was about 0.04–0.11, and the fluorescent lifetime (τ) was about 0.5–1.2 ns. On the other hand, for the Fe and Ln-complexes, the QE of TX rings was below 0.01, which was attributed to the reason that the excited energy of the TX rings was quenched by ligand-Fe2+ charge transfer or by transferring the energy to the central Ln3+ (Eu3+ and Tb3+) ions. Thus, the Ln-TXOBPy and Ln-TXOTPy complexes gave off strong and sharp Eu3+/Tb3+ emissions at the wavelengths between 480 and 750 nm. The fluorescent emission lifetime of the central Ln3+ ions was about 0.3–0.6 ms. Thus, we can suggest that the TXOBPy and TXOTPy photoinitiators can act as potential candidates for the development of efficient emitters with tunable light emissions and luminescent sensors.