Solvent-driven luminescence modulation/switching in an iridium(iii) complex containing an aldehyde group

Abstract

Complex [Ir(dfppy)₂(phca)]PF₆ (1) has been synthesized, which contains an aldehyde group in the N^N ligand phca = 1,10-phenanthroline-4-carbaldehyde, with the aim of exploring solvent-driven luminescence modulation/switching in this complex. Complex 1 shows green emission at 514 nm in CH₃OH, while orange phosphorescence with the emissions at 516 and 624 nm in CH₂Cl₂. The solid-state structure of 1 is dependent on the crystallization solvent used, forming a red solid 1^R in CH₂Cl₂, while a yellow solid 1^Y in CHCl₃. The neighboring [Ir(dfppy)₂(phca)]⁺ cations in solid 1^R are held together by π⋯π stacking interactions, while by van der Waals interactions in solid 1^Y. The distinct packing structures of 1^R and 1^Y lead to their significantly different solid-state luminescence, weak orange phosphorescence for 1^R (emission at 620 nm, Φ = 3.3%) and strong yellow phosphorescence for 1^Y (emissions at 532 and 558 nm, Φ = 46.6%). Both 1^R and 1^Y show CH₂Cl₂/CHCl₃-driven phosphorescence switching between orange and yellow, due to their structural interconversion through recrystallization. Moreover, the emission color of 1^Y can be reversibly switched between yellow and orange through alternate pressing and recrystallization in CHCl₃. This work discusses the relationship among the solvent, the structure and the luminescence modulation/switching of complex 1.