Mechanochemical changes on cyclometalated Ir(iii) acyclic carbene complexes – design and tuning of luminescent mechanochromic transition metal complexes

Abstract

A new class of luminescent cyclometalated Ir(iii) complexes with readily tunable mechanochromic properties derived from the mechanically induced trans-to-cis isomerization have been developed.

Study of a phosphorescent cationic iridium(iii) complex displaying a blue-shift in crystals

“…It is worth noting that the present result differs from previous reports, where crystalline powders (PXRDs displayed sharp and intense diffraction peaks) were obtained with cationic iridium complexes either by evaporation of the solvents after chromatography column or by rapid recrystallization/precipitation. 23,36,39,40,74,76 In contrast, the crystals, collected indiscriminately from the same batch of crystallization, display a different pattern than the powder (Figure S8) with sharp peaks, which pattern is similar to the calculated one from the crystal structure.…”

“…The complex displays different colours in the powder and crystal forms, which may be related to polymorphism. 23,36,38,[73][74][75] The powder XRD pattern displays three undefined humps roughly centered at 10 °, 19 ° and 37 °. The absence of fine peaks demonstrates that the precipitated powder is amorphous.…”

“…In contradiction, some other complexes display low or almost no luminescence in solution and the "turning on" of the luminescence is triggered by aggregation either by the introduction of a non-solvent or in the solid state (powder, neat spin-coated film or drop casted film…). This behaviour has been called in different manner "enhanced phosphorescence emission in the solid state" (EPESS) and "aggregation-induced phosphorescent emission" (AIPE) 6,[21][22][23] , depending if the complex displays in dilute solution a weak emission or no detectable emission, respectively. In all these cases, the complexes skeleton demonstrates flexibility in solution, and thus the excitation energy is dispersed thermally.…”

“…20 Changes in the emission wavelength in the solid state is quite common especially looking at the neat solid (powder, neat thin film and crystal). The large majority of the cationic iridium(III) complexes display a bathochromic shift in solid state, 17,23,[32][33][34][24][25][26][27][28][29][30][31] whereas only few contributions report iridium(III) complexes displaying a hypsochromic shift. 17,27,40,[32][33][34][35][36][37][38][39] If bathochromic shifts could be easily rationalized with the presence of intermolecular interactions, such as - interactions, 14 blue shifted emission spectra in solid state are less straightforward dealing with neat solid.…”

Tuning the luminescence of transition metal complexes with acyclic diaminocarbene ligands

“…Species 48–53 were prepared by the replacement of the chloride ligand of isocyano precursors with substituted 2-aminopyridines followed by an intramolecular nucleophilic attack (Scheme 6). 49 48–53 exhibit two moderate absorption shoulders at 340–360 and 420–440 nm, ascribed to an admixture of LC and MLCT [ d π (Ir) → π*( C , N -ADC)] transitions. In solution, complexes 48–53 display intensive triplet photoluminescence at RT with Φ ranging from 0.25 to 0.59 (Fig.…”