Manipulation Of Potential Energy Surfaces Of Binuclear Platinum Complexes And Their Application As Viscosity Senso

Photoinduced structural change (PSC) is a fundamental excited-state dynamic process in chemical and biological systems, e.g. photoinduced flattening distortion of Cu(II) complexes1, PSCs of binuclear Pt (II) complexes2, 3. This process is highly dependent on the configuration of molecular excited-state potential energy surfaces (PESs). However, due to the lack of guidelines and approaches for designing excited-state PESs, precise manipulation of PSC processes is still very challenging. In this project, a series of rationally designed butterfly-like phosphorescent binuclear platinum complexes were synthesized with well-controlled PESs and tunable dual emissions at room temperature. We demonstrated our capability to manipulate PESs in two ways. First, we introduce the steric bulkiness effect of both cyclometalated ligands and pyrazolate bridging ligands to control the transition energy barrier of PSC process. Based on the Bell-Evans-Polanyi principle, which describe a chemical reaction between two energy minima on the first triplet excited-state PES, we reveal a simple method to engineer the dual emission of molecular systems by manipulating PES and therefore PSC to achieve desired molecular properties. Second, we synthetically control the electronic structure of the cyclometallating ligand and the steric bulkiness of the pyrazolate bridging ligand at the same time to realize the precise manipulation of the PESs. Color tuning of dual emission from blue/red, to green/red and red/deep red have been achieved for these phosphorescent molecular butterflies, which have two well-controlled energy minima on the PESs. The environmentally dependent photoluminescence of these molecular butterflies enabled their application as self-referenced luminescent viscosity sensor.