Structural Tuning of Boron Difluoride Formazanate Electrochemiluminescence Mediated by Tri-n-propylamine

Abstract

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.

Unveiling the Hidden, Dark, and Short Life of a Vibronic State in a Boron Difluoride Formazanate Dye

“…We must therefore conclude that the t =0 μs excitation is to a different and higher‐energy state, however, it also does not have a clear 0–0 transition and additionally, each of the two states that we identify from the excitation spectra gives rise to the same emission spectrum (Figures B,D and A). Therefore, in Figure , we have shown the planar excited‐state relaxed geometry for S 1 * that has been previously reported as the emitting state . To assess the possible emission maximum from this relaxed state, we calculated the absorption spectrum from S 0 to S 1 * with a fixed planar geometry.…”

“…A major proposed difference between the geometries of the electronic states of BODIPY dyes and BF 2 formazanate dyes is that the excited state geometry of the BF 2 formazanate dyes changes from the folded ground state to a planar, emissive excited state . In this paper, we examine the electronic origins of both the absorption and the emission spectral data for a prototypical BF 2 formazanate dye, 2 , which exhibits both a high molar absorptivity and emission quantum yield.…”

Formazanate coordination compounds: synthesis, reactivity, and applications

“…The most dramatic difference found within this series is the fact that F PL values for BF 2 triarylformazanates are generally very low and often o1% and Stokes shifts for the same species are generally larger than those of 3-cyano and 3-nitro derivatives. The latter trait can be linked to the strictly planar structure adopted by these species in the excited state, as discussed above, 65,74,75 while the former has been attributed to enhanced probability of non-radiative decay associated with vibration and/or free rotation of the 3-aryl substituents. This hypothesis was tested by examining the protonation of compound 59 Py to form 59 Py ÁH + , which possesses a 2-pyridyl substituent at the 3-position of the formazanate backbone.…”

“…9). 73,75,81 The CV of a solution containing BF 2 formazanate 60d and an excess of TPrA is shown in Fig. 9A.…”

Near‐Infrared Photoluminescence and Electrochemiluminescence from a Remarkably Simple Boron Difluoride Formazanate Dye

“…(4)].O n scanning to more positive potentials,asecond ECL maximum was observed at ap otential of 0.95 V. At this potential, the solution likely contains significant quantities of electrogen-erated 3 2+ and TPrAC.Wepostulate that 3 2+ and 3 can undergo ac omproportionation reaction based on previous computational studies [Eq. (5)], [25] and that lower ECL intensity in this region likely relates to the two-step process required to generate 3C + in the vicinity of the working electrode at these higher potentials.…”