Material Profiling for Photocrystallography: Relating Single-Crystal Photophysical and Structural Properties of Luminescent Bis-Cyclometalated Iridium-Based Complexes

Abstract

The photophysical properties of seven luminescent iridium complexes are characterised in their single-crystal form and the photo-activity is related to their molecular structures. Specifically, solid-state optical emission spectra and associated lifetimes are determined from single crystals of iridium complexes containing three bidentate ligands: two variously substituted 2phenylbenzothiazoles and either a 2,4-pentadione (acetylacetone) or 2-pyridinecarboxylic (picolinic) acid. All complexes studied exhibit emissive behaviour in the solid-state which originates from 3 * and metal-to-ligand-charge-transfer (MLCT) electronic transitions; this is supported by density functional theory. Phosphorescence is observed in all cases with microsecond lifetimes, ranging from 0.30-2.4 s at 298K and 1.4-4.0 µs at 100 K. Structureproperty relationships are established which are relevant to the potential solid-state application of this series of luminescent complexes as organic light emitting diodes (OLED) material components. In addition, these materials are assessed for their suitability to time-resolved pump-probe photocrystallography experiments, which will reveal their photo-excited-structure. Accordingly, the design process by which materials are selected, and technical parameters are defined, for a photocrystallography experiment is illustrated. This family of complexes presents a case study for this photocrystallography material profiling. Results show that the time-resolved photo-excited state structure, featuring the MLCT transition is, in principle at least, viable for two of these complexes.

Uncovering the role of non-covalent interactions in solid-state photoswitches by non-spherical structure refinements with NoSpherA2

“…the relative kinetic lability of the differing metal centres, and steric influences from the surrounding crystal lattice. Many of these factors have been discussed by us 5,28,35,36 and others [37][38][39][40][41][42][43] previously, and this conclusion highlights the complexity of rationally-designing solid-state photoswitchable crystals and the importance of considering the many, and often competing, influential factors that govern the photoreaction.…”

Rational design of efficient photosensitizers based on cyclometalated iridium(iii) complexes with 2-arylbenzimidazole and aromatic 1,3-diketone ligands

“…This is typical of ligands bearing compact fluorine substituents and is due to competitive steric and electronic effects. [44][45][46] Because of close structural similarity, the isomers crystallize together with the ratio of 4 : 1 (single-crystal), although this does not necessarily represent the entire mixture. The 1 H NMR spectrum of the mixture (Fig.…”