Photophysical Study on the Rigid Pt(II) Complex [Pt(naphen)(Cl)] (Hnaphen = Naphtho[1,2-b][1,10]Phenanthroline and Derivatives

The electrochemistry and photophysics of the Pt(II) complexes [Pt(naphen)(X)] (Hnaphen = naphtho[1,2-b][1,10]phenanthroline, X = Cl or C equivalent to CPh) containing the rigid tridentate (CNN)-N-boolean AND-N-boolean AND-coordinating pericyclic naphen ligand was studied alongside the complexes of the tetrahydro-derivative [Pt(thnaphen)(X)] (Hthnaphen = 5,6,8,9-tetrahydro-naphtho[1,2-b][1,10]phenanthroline) and the (NCN)-C-boolean AND-N-boolean AND-coordinated complex [Pt(bdq)(Cl)] (Hbdq = benzo[1,2-h:5,4-h']diquinoline. The cyclic voltammetry showed reversible reductions for the (CNN)-N-boolean AND-N-boolean AND complexes, with markedly fewer negative potentials (around -1.6 V vs. ferrocene) for the complexes containing the naphen ligand compared with the thnaphen derivatives (around -1.9 V). With irreversible oxidations at around +0.3 V for all of the complexes, the naphen made a difference in the electrochemical gap of about 0.3 eV (1.9 vs. 2.2 eV) compared with thnaphen. The bdq complex was completely different, with an irreversible reduction at around -2 V caused by the (NCN)-C-boolean AND-N-boolean AND coordination pattern, which lacked a good electron acceptor such as the phenanthroline unit in the (CNN)-N-boolean AND-N-boolean AND ligand naphen. Long-wavelength UV-Vis absorption bands were found around 520 to 530 nm for the (CNN)-N-boolean AND-N-boolean AND complexes with the C equivalent to CPh coligand and were red-shifted when compared with the Cl derivatives. The (NCN)-C-boolean AND-N-boolean AND-coordinated bdq complex was markedly blue-shifted (493 nm). The steady-state photoluminescence spectra showed poorly structured emission bands peaking at around 630 nm for the two naphen complexes and 570 nm for the thnaphen derivatives. The bdq complex showed a pronounced vibrational structure and an emission maximum at 586 nm. Assuming mixed (LC)-L-3/(MLCT)-M-3 excited states, the vibronic progression for the (NCN)-C-boolean AND-N-boolean AND bdq complex indicated a higher LC character than assumed for the (CNN)-N-boolean AND-N-boolean AND-coordinated naphen and thnaphen complexes. The blue-shift was a result of the different (NCN)-C-boolean AND-N-boolean AND vs. (CNN)-N-boolean AND-N-boolean AND coordination. The photoluminescence lifetimes and quantum yields phi(L) massively increased from solutions at 298 K (0.06 to 0.24) to glassy frozen matrices at 77 K (0.80 to 0.95). The nanosecond time-resolved study on [Pt(naphen)(Cl)] showed a phosphorescence emission signal originating from the mixed (LC)-L-3/(MLCT)-M-3 with an emission lifetime of around 3 mu s.

Automated summary

The electrochemical and photophysical properties of Pt(II) complexes containing different ligands were studied, showing varied reduction potentials and absorption spectra. The naphen ligand resulted in a lower electrochemical gap compared to the tetrahydro derivatives. The coordination pattern of ligands also influenced the emission properties, with different complexes exhibiting varying photoluminescence lifetimes and quantum yields.