The syntheses, crystal structures, electronic absorption spectra, electrochemical properties, and photophysical properties of a series of copper(I) bis(phenanthroline) complexes are reported. The phenanthroline ligands that have been prepared and investigated are the following: dop (2,9-di-(2-methylphenyl)- 1,10-phenanthroline), xop (2-(2-methylphenyl)-9-(2,6-dimethylphenyl)-1,10-phenanthroline), dpep (2,9-diphenylethynyl-1,10-phenanthroline), and dmesp (2,9-dimesityl-1,10-phenanthroline). The complex [Cu(dop)(2)](PF6) . Et2O crystallizes in space group P (1) over bar with a = 11.854(3) Angstrom, b = 14.705(3) Angstrom, c = 15.866(4) Angstrom, alpha = 107.81(2)degrees, beta = 106.72(2)degrees, gamma = 97.56(2)degrees, V = 2447.6(10) Angstrom(3), and Z = 2. For 5739 unique data with F > 4.0 sigma(F), R = 7.52%. The complex [Cu(xop)(2)] (PF6) . 3/2CH(3)OH crystallizes in space group C2/e with a = 23.096(6) Angstrom, b = 23.387(6) Angstrom, c = 17.873(7) Angstrom, beta = 100.08(3)degrees,V = 9505(5) Angstrom(3), and Z = 8. For 5631 unique data with F > 4.0 sigma(F), R = 6.02%. The complex [Cu(dpep)(2)](PF6) crystallizes in space group P (1) over bar with a = 13.327(7) Angstrom, b = 14.114(7) Angstrom, c = 15.175(5) Angstrom, alpha = 87.23(4)degrees, beta = 66.48(3)degrees, gamma = 61.84(4)degrees, V = 2273(2) Angstrom(3), and Z = 2. For 4851 unique data with F > 4.0 sigma(F), R = 5.47%. The complex [Cu(dmesp)(dpep)](PF6) crystallizes in space group Pbca with a = 14.547(6) Angstrom, b 22.868(6) Angstrom, 30.659(10) Angstrom, V = 10199(6) Angstrom(3), and Z = 8. For 2281 unique data with F > 4.0 sigma(F), R = 9.43%. The electrochemical, spectral, and structural properties of [Cu(dop)(2)](+) and [Cu(xop)(2)](+) demonstrate that the copper coordination environment is more sterically encumbered and more rigid in these two complexes than the coordination environment in the comparison molecule [Cu(dpp)(2)](+) (dpp = 2,9-diphenyl-1,10-phenanthroline). A larger energy gap is predicted for [Cu(dop)(2)](+) and [Cu(xop)(2)](+) based on these data, and consequently, a blue-shifted emission is observed relative to [Cu(dpp)(2)](+). The room-temperature excited-state Lifetimes in dichloromethane and methanol of the dop and xop complexes are shown to be shorter than the dpp complex, and these results are interpreted as due to a reduction in ligand pi-electron delocalization in the former two complexes. The complexes [Cu(dpep)(2)](+) and [Cu(dmesp)(dpep)](+) are shown to have increased ligand pi-electron delocalization relative to [Cu(dpp)(2)](+); however, neither complex displays room-temperature steady-state emission in dichloromethane.