Studies On The Synthesis And Properties Of Imidazoline Ligands And The Corresponding Complexes

In this thesis, five 2-arylimidazoline ligands and the corresponding cycioplatinated complexes were synthesized and their photoluminescent properties were studied. The main results were shown in the following:1. Synthesis and structural characterization of novel cycioplatinated complexes with 2-arylimidazolines2-arylimidazoline ligands 2a-2d were synthesized from benzoyl chloride or p-methoxybenzoyl chloride with aminoethanol or valinol and 2e was synthesized from 2-phenylimidazoline. Among them, 2d was a new compound. Then treatment of K₂PtCl₄ with 2 equiv of ligand 2 produced the proposed chloro-bridged dimer, which was subsequently converted into the expected cycioplatinated complexes 3 upon reaction with acetylacetone (acac) in the presence of Na₂CO₃ in 2-ethoxyethanol (Scheme 1). All the new compounds were well characterized by elemental analysis, IR, ¹H NMR, ¹³C NMR and ESI-MS. Furthermore, the molecular structures of both 3c and 3d were determined by X-ray single crystal analysis.2. Photoluminescent properties of novel cycioplatinated complexes with 2-arylimidazolinesAll the UV-vis spectra of complexes 3 in CH₂Cl₂ have similar features. The intense absorption bands at wavelengths below 300 ran are attributed toÏ€-Ï€^* transitions of the ligands. In addition, all of the complexes have a broad, less intense absorption band atλ_max 347-364 nm, which tails beyond 400 nm. It can tentatively be assigned to MLCT transition resulting from the promotion of an electron from Pt(d) HOMO to theÏ€^* LUMO on the 2-arylimidazoline ligand. The change of the substituent on N-l of the ligand from C₆H₅(3b) to p-CH₃C₆H₄(3a) or p-OCH₃C₆H₄ (3c) or even CH₂C₆H₅(3e) has very little effect on the position of this band (λ_max around 363 nm), if any. However, this absorption is slightly blue-shifted for complex 3d (λ_max 347 nm) with electron-donating group (OMe) on 2-aryl ring.The substituents on N-1 greatly influence the fluorescent emission properties of ligands 2 in CH₂Cl₂ solution at room temperature. Thus, changing the substituent from p-CH₃C₆H₄(2a) or C₆H₅(2b) to more electron-donating aryl group such as p-OCH₃C₆H₄(2c or 2d) leads to an obvious red shift of the emission maximum (368 nm and 370 nm vs 482 and 465 nm) and a significant increase in emission intensity. For ligand 2e with CH₂Ph on N-1, it displays emissions at 344 and 406 nm with similar intensity to that of 2a and 2b. Upon photoexcitation, all the platinum complexes studied also show emission in CH₂Cl₂ solution at room temperature. Different from the substituent effects in ligands 2, the change of the substituent on N-1 from p-CH₃C₆H₄(3a) or C₆H₅(3b) to p-OCH₃C₆H₄(3c) has no significant effect on the room-temperature emission properties of the complexes and these three compounds show very similar spectra to one another, with emission maxima around 560 and 590 nm. A possible reason for the result is that the N-aryl is unconjugated with the other parts of the complex which is confirmed by X-ray single crystal analysis of 3c and 3d. On the other hand, the emission peaks of complex 3d with a methoxy group on 2-aryl ring and 3e with CH2Ph on N-1 are subject to a small blue shift. For 3d, the emission intensity also increases. The above results give some useful information on further ligand modification for tuning the emission properties of the related platinum complexes.