Cyclometalated Platinum(II) Complexes in a Cis-N,N Configuration: Photophysical Properties and Isomerization to Trans Isomers

Synthesis, isomerization, and photophysical properties of novel cis-N,N-cyclometalated complexes [Pt(C<^>N)(L-Phe)] (C<^>N = benzoquinolinate (1), phenylpyridinate (2), 2-(p-tolyl)-pyridinate (3), and 1-phenylpyrazolate (4); L-Phe(-) = L-phenyl-alaninate) are reported herein. In solution, the cis forms of the complexes isomerize to their trans forms via an associative mechanism. This cis/trans isomerism barely influences the absorption and luminescence properties of the complexes in solution, except for a characteristic absorption at approximately 340 nm in the absorption spectra of the cis complexes that is not observed for the trans complexes. Interestingly, the cis complexes are spontaneously assembled in a crystalline phase and show bathochromic absorption and emission colors compared with those of the corresponding trans isomers, which are aggregated in an amorphous phase. cis-1 and cis-2 demonstrate hypsochromic luminescence mechanochromism. The influence of the geometrical isomerism on the photophysical properties and the isomerization mechanism are supported by density functional theory calculations.

Automated summary

The synthesis, isomerization, and photophysical properties of a series of novel cis-N,N-cyclometalated complexes [Pt(C^N)(L-Phe)] were reported. The isomerization process from cis to trans forms did not significantly affect the absorption and luminescence properties in solution, except for a characteristic absorption peak observed for cis complexes. Interestingly, the cis complexes showed different absorption and emission colors in a crystalline phase compared to the trans isomers in an amorphous phase, indicating potential applications in optoelectronic devices.