Exploring Intertrimer Cu•••Cu Interactions and Further Phosphorescent Properties of Aryl Trimer Copper(l) Pyrazolates via Substituent Changing and External Pressure

To explore the effect of intertrimer Cu center dot center dot center dot Cu interactions on the phosphorescent properties of trimeric copper(l) pyrazolates, three new complexes with identical core cluster structures and different substituents, {[3,5-(Me)(2)-4-(Ph)Pz]Cu}(3) (MPC-P), {[3,5-(Me)(2)-4-(1-Naph)Pz]Cu}(3) (MPC-N), and {[3,5-(Me)(2)-4-(9-Anthr)Pz]Cu}(3) (MPC-A), were synthesized. The intertrimer Cu center dot center dot center dot Cu distances of the three complexes were obtained from X-ray crystallographic data or molecular dynamics simulations. The phosphorescent properties of the three complexes were investigated at various pressures. At ambient pressure, the emissions of the three complexes were dramatically different from each other. For MPC-P, the main emission band was identified as phosphorescence and MPC-N gave a predominant emission of fluorescence and a weak emission of phosphorescence. When the substitutent was replaced by an anthryl group in MPC-A, no phosphorescence was observed, except for a strong fluorescence band. The phosphorescence of the trimer copper(l) pyrazolates was assigned to the excited-state dimer/polymer *[Cu-3](n) with LMCT characteristics. Under higher external pressures, only phosphorescent intensities of MPC-P showed considerable enhancement at pressures up to 2 GPa. External pressure reduced the intertrimer Cu center dot center dot center dot Cu distances of MPC-P and enhanced the phosphorescence intensities, providing a direct evidence to support the assignment of phosphorescence.