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-phenylalaninate) 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.