| Summary: | 碩士 === 輔仁大學 === 化學系 === 107 === For this work, we synthesized four CM-Ru-bpy (CM = cyclometalated ligand) chromophore type complexes to explore phosphorescence properties with an argument of spin-orbit coupling (SOC) mediating phosphorescence radiation with singlet transition parameters for Ru-bpy chromophores, where bpy = 2,2’-bipyridine, CM = ppy (2-phenylpyridine), ppm (2-phenylpyrimidine), dpz (2,3-diphenylpyrazine) and dpy (1,4-diazatriphenylene). The previous work by Selbin and Felix et al. reported the phosphorescence properties of [Ru(bpy)2(ppy)]+ ion as a typical Ru-bpy chromophore.
The electrochemistry results of CM-Ru-bpy ions represent relatively small E1/2 (RuIII/II) potential, their E1/2 (RuIII/II) vs. Ag/AgCl are in range of 0.5 ~ 0.6 V contrasting to the E1/2 (RuIII/II) of [Ru(bpy)3]2+ (1.32 V) and of [Ru(bpy)2(en)] 2+ (0.96 V). Furthermore, the E1/2 (bpy0/-1) amplitude of [Ru(bpy)n(Am)6-2n]2+ (n = 1 ~ 3, typical Ru-bpy ions) and CM-Ru-bpy ions are in the same range of -1.3 ~ -1.7 V. The absorption of CM-Ru-bpy ions show two low-energy intense metal-to-ligand charge transfer (MLCT) bands and each of them split into two peaks, for which is contrasted to a single low-energy MLCT band of the typical Ru-bpy chromophore.
DFT results indicate the observed low-energy absorption band of CM-Ru-bpy (CM = ppy, ppm) ions are most of the 1MLCT (Ru-bpy) transitions contribution, and of CM-Ru-bpy (CM = dpz, dpy) ions are mixed of the 1MLCT (Ru-bpy) and 1MLCT (Ru-CM) transitions contribution. The calculated T1 excited-state for all of CM-Ru-bpy ions is the 3MLCT (Ru-bpy) excited-state, and the low-energy Tn excited-state of CM-Ru-bpy (CM = dpz, T5; dpy, T4) ions show 3MLCT (Ru-CM) excited-state.
The photophysic parameters of non-radiative rate constant (kNRD) for typical Ru-bpy and simple type of CM-Ru-bpy (CM = ppy, ppm) ions show the similar relaxation behaviors of Ru-bpy chromophore, but the radiative rate constant (kRAD) of CM-Ru-bpy ions represent average two times amplitudes than of typical Ru-bpy chromophore. Furthermore, the 77 K two exponential emission decay lifetime curves of CM-Ru-bpy (CM = dpz, dpy) ions indicate that the dual emission behaviors are attributed to the low-energy 3MLCT (Ru-bpy) and 3MLCT (Ru-CM) emitting states.
Finally, we represent that the radiative efficiency, kRAD/(vem)3, amplitudes of the Ru-bpy chromophores emitting for CM-Ru-bpy and typical Ru-bpy ions dependent on the SOC mediation of the singlet-transition moment contributions, where vem is the emission energy, and the relatively high kRAD/(vem)3 amplitude of CM-Ru-bpy ions can be attributed to the relatively great contribution of SOC mediating 1MLCT Oscillator strength.
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