Photophysics of\n3‑Carboxy-Salicylideneaniline\nin Rare Earth Metal Complexes with Silicon-Containing Schiff Base\nLigands

The investigations reported in this work concern the\ncapabilities\nof the 3-carboxy-salicylidene unit in three dicompartmental Schiff\nbases with a flexible spacer bearing silane or siloxane units to efficiently\ncoordinate rare earth and transition-metal ions as well as the efficiency\nto act as antenna or organometallic antenna for Ln(III) sensitization.\nThe Ln(III) complexation studies of the H<sub>4</sub><b>L1</b>, H<sub>4</sub><b>L2</b>, and H<sub>4</sub><b>L3</b> ligands\nwere performed by spectrophotometric titration. The selectivity toward\nseven Ln(III) ions and the trend of the stability constants are analyzed\nin connection with the structure of the ligands. In order to find\nthe energetic factors that impact the efficiency of Ln(III) sensitization,\nthe corresponding Gd(III) complexes were prepared and were in-depth\nanalyzed from the point of view of the photophysical properties. The\ninvestigations were carried out using time-resolved emission and transient\nabsorption spectroscopy. Phosphorescence data prove the unhindered\npath of the ligands to the triplet state and the probability to transfer\nthe excitation energy to the Ln(III) ion. Applicability of two selected\nGd(III) complexes in detection and recognition of transition and heavy\nmetal ions has been studied with a double purpose: to evaluate their\nsensitivity and recognition ability so that they could be applied\nin pollutants detection and to estimate the capability of the M(II)-Schiff\nbase unit as an organometallic antenna for Visible emission sensitization.\nThe Gd(III) complex with a long π-conjugation showed multiple\nfluorescence responses to various kinds of 3d ions, which gave it\npattern recognition ability. The discrimination power was finally\nanalyzed by a principal component analysis.