Electrochemistry and electrogenerated chemiluminescence (ECL) of boron difluoride formazanate complexes bearing p-methoxyphenyl N-substituents were studied experimentally and computationally. It was shown that the substituents at the 3-position (R 3) of the formazanate backbone play a critical role in the electrochemistry and ECL of the complexes in the presence of tri-n-propylamine (TPrA). The ECL emission of 1a (R 3 = cyano), 1b (R 3 = phenyl), and 1c (R 3 = p-C 6 H 4 OMe) occurred at peak wavelengths of 724 nm (1.71 eV), 704 nm (1.76 eV), and 723 nm (1.71 eV), consistent with their photoluminescence maxima. The maximum ECL quantum yields, determined relative to the [Ru(bpy) 3 ] 2+ /TPrA system, were 450% for 1a, 244% for 1b, and 94% for 1c, respectively. The relatively large Stokes shifts of 1a-1c were linked to the flattening of these molecules which accompanies their electronic excitation. Through the use of spooling ECL spectroscopy, it was demonstrated that the intensity and relative energies of ECL emission from boron difluoride formazanate complexes can be readily tuned via structure modification, variation in applied potential, and/or scan rate.