Crowded Cu(I) complexes involving benzo[h]quinoline:: π-stacking effects and long-lived excited states

The Friedlander condensation was employed to synthesize two series of 3,3 ' -polymethylene bridged ligands, L, based on 2-(2 ' -pyridyl)-benzo[h]quinoline and 2,2 ' -bibenzo[h]quinoline (BHQ) along with the fully aromatic naphtho[1,2-b]-1,10-phenanthroline. Complexes [Cu(L)(2)](+) were prepared as their perchlorate or hexafluorophosphate salts. The solution state structures were analyzed by NMR and shielding effects reflected significant interligand pi -stacking interaction in the complexes. Solid-state structures of the complexes where L = 3,3 ' -tetramethylene-2,2 ' -bibenzo[h]quinoline or naphtho[1,2-b]-1,10-phenanthroline were determined by X-ray analysis. The tetramethylene bridged complex showed a highly distorted coordination geometry with the BHQ rings of opposing ligands pi -stacked at a interplanar distance of about 3.37 Angstrom. Complexes of the BHQ series showed a pronounced MLCT absorption maximum which shifted bathochromically from 496 to 610 nm as the 3,3 ' -bridge decreased from 4 to 2 carbons. The BHQ complexes luminesced strongly in CH2Cl2 solution and the tetramethylene-bridged system showed the longest yet recorded excited-state lifetime for a copper MLCT excited state, tau = 5.3 mus and Phi = 0.10.