Temperature-Responsive Fluorescent Organoplatinum(II) Metallacycles

The synthesis, characterization, and temperature-responsive properties of two fluorescent organo­platinum­(II) metalla­cycles are reported. Metalla­cycles <b>M1</b> and <b>M2</b> were prepared via the coordination-driven self-assembly of a 120° triaryl­amine ligand <b>L1</b> and a 120° diplatinum­(II) acceptor <b>Pt-1</b> or 180° diplatinum­(II) acceptor <b>Pt-2</b>, respectively. <b>M1</b> and <b>M2</b> are hexagonal metalla­cycles, comprising of three or six freely rotating anthracene pendants on their periphery, respectively. In response to the temperature variation between −20 and 60 °C, the ligand displays irregular emission changes, whereas both metalla­cycles show reversible absorption and emission spectral changes in THF. The changes in their green emission intensity also exhibit a linear correlation with the temperature variation, with an average sensitivity of −0.67% and −0.77% per °C for <b>M1</b> and <b>M2</b>, respectively. Furthermore, in coordinating solvents, such as DMF and CH₃CN, <b>M1</b> and <b>M2</b> show different behaviors: in the lower temperature range, i.e., below 30 °C, their spectral changes are similar to those observed in THF; however, at a higher temperature the metalla­cycles were presumably destroyed by the solvents and displayed ratiometric fluorescent responses, including a cyan emission of the ligand <b>L1