Cu^(I)(2,9-Bis(trifluoromethyl)-1,10-phenanthroline)₂⁺ Complexes:  Correlation between Solid-State Structure and Photoluminescent Properties

The 90K solid-state structures, room temperature absorption, and room temperature and 17 K emission spectra of seven different salts of [Cu(I)(bfp)₂]⁺ (bfp = 2,9-bis(trifluoromethyl)-1,10-phenanthroline) have been determined. To quantify the distortion of the Cu coordination environment, a distortion parameter ζ is defined that is a combined measure of the flattening, rocking, and wagging distortions of the complex cations. In general, the distortion in the (bfp) cations is less than found previously for Cu(I)(dmp)₂ (dmp = 2,9-dimethyl-1,10-phenanthroline) salts, in particular the flattening is reduced because of the bulkier 2,9-substituents. The 17 K lifetimes range up to 1.8 μs in the series of solids examined and, with the marked exception of the BF₄^- salt, correlate linearly with the distortion parameter ζ. The emission wavelength red-shifts with decreasing lifetime, which implies that an increased ground-state distortion is associated with a smaller energy gap.