Pyrene-based cycloplatinated carbene regioisomers: synthesis, structures and probing the site-effect on the...

Herein we report the synthesis and characterization of two families of square planar cyclometalated NHC-platinum complexes of the type [Pt(C^C*)(L)] (1-7), displaying a pyrenyl-N-heterocyclic carbene chromophore with (C^C*) = (pyrenyl-^RNHC) and where L is a monoanionic β-diketonate ancillary ligand {R = Me, L = acac (1); R = Me, L = ^tBuacac (2); R = nBu, L = acac (3); R = -CH₂-naph, L = ^tBuacac (4); R = Me, L = acac (5); R = Me, L = ^tBuacac (6) and R = Me, L = ^Phacac (7)}. Complexes 1 and 5 were described previously. These complexes are obtained as two regioisomers in which the carbene unit is specifically attached either at the C1 or C2 site of the pyrene chromophore. The X-ray molecular structures of 1, 2 and 4 confirm the identity of the 1-regioisomeric Pt-compounds. Furthermore, the structures of 5 and 7 were also obtained, proving the identity of the 2-regioisomeric Pt-complexes. This unique class of molecules containing both organic and inorganic chromophores displays phosphorescent emissions in the red region of the visible spectrum. Interestingly, the less explored regioisomers, i.e. those bearing the carbene unit at the C2-position of the pyrene and the Pt-center at C1, feature higher emission quantum yields, highlighting the importance of the site-effect.