Electrogenerated chemiluminescence (ECL) is the process in which electrogenerated species undergo electron transfer reactions to form excited states that emit light. Many molecules have the potential to produce ECL, however Ru(bpy) 3 2+ (bpy = 2,2′‐bipyridine) is the most common emitter used for analytical applications. Application of a voltage to an electrode in the presence of an emitter induces light production and allows for the detection of the emitter at very low concentrations. Advantages over other analytical methods include low backgrounds, precise spatial and temporal control over the emission, and the possibility of signal amplification. Commercial systems exist that use ECL to detect numerous clinically relevant analytes with high sensitivity using a variety of assay formats.

Fissure coupling of the fluoranthene adduct (7,12-diphenyl)benzo[k]fluoranthene (3) using AlCl3/NaCl, CoF3/TFA, or Tl(OCOCF3) gave the new polyaromatic hydrocarbon dibenzo{[f,f’]-4,4’,7,7’-tetraphenyl}diindeno[1,2,3-cd:1‘,2‘,3‘-lm]perylene (4). Crystal data for 4:  triclinic space group P1̄, a = 10.569(2) Å, b = 11.565(4) Å, c = 13.001(3) Å, α = 95.05(2)°, β = 111.24(1)°, γ = 100.53(1)°, Z = 1, R F = 0.075%. Compounds 3 and 4 are both highly fluorescent in solution and display relative fluorescence quantum yields of φF = 1.0 and 0.85, respectively. The electrochemistry and electrogenerated chemiluminescence (ECL) of each compound has been investigated. The cyclic voltammogram of 3 in benzene−acetonitrile (9:1) shows that the compound undergoes a reversible reduction and an irreversible oxidation, whereas the cyclic voltammogram of 4 displays the reversible formation of both singly and doubly charged cations and anions. Compounds 3 and 4 undergo ECL to yield blue and orange-red light, respectively, with an ECL efficiency of ∼2% for 4. Emission from 4 is observed in the ECL of unstirred solutions of 3. This indicates that 4 is produced at the electrode during the ECL experiment, presumably via an electrochemical oxidative coupling process during the anodic potential steps.

Upon oxidation at a platinum electrode, (7,12-diphenyl)benzo[k]fluoranthene (1) undergoes intermolecular dehydrogenative coupling to form bis-4,4'-(7,12-diphenyl)benzo[k]fluoranthene (2). Further oxidation of this product results in a much slower intramolecular coupling reaction that yields dibenzo{[f,f']-4,4',7,7'-tetraphenyl}diindeno[1,2,3-cd:1',2',3'-lm]perylene (3). 2 can be synthesized via bulk electrolysis of 1 and also by the chemical coupling of 4-bromo-7,12-diphenylbenzo[k]fluoranthene (4) with a nickel catalyst. Compounds 1-3 are capable of electrogenerated chemiluminescence (ECL), and their coupling reactions have been detected and followed using this technique. Cyclic voltammograms of 1 have been digitally simulated to provide mechanistic and kinetic insight into the initial intermolecular oxidative coupling reaction. Evidence supports an EC(2)()EE mechanism, in which the coupling of radical cations of 1 is the rate-limiting step. A second-order rate constant of k = 7500 M(-)(1) s(-)(1) has been determined for the dimerization process by fitting experimental data to theoretical working curves.

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Re(L)(CO) 3 Cl complexes (where L is 1,10-phenanthroline, 2,2′-bipyridine, or a phenanthroline or bipyridine derivative containing methyl groups) are photoluminescent in fluid solution at room temperature. In acetonitrile solutions, these complexes display one chemically reversible one-electron reduction process and one chemically irreversible oxidation process. λ max for the luminescence is dependent on the nature of L, and a linear relationship between λ max and the difference in electrode potentials for oxidation and reduction is evident. Electrogenerated chemiluminescence (ECL) was observed in acetonitrile solutions of these complexes (Bu 4 NPF 6 as electrolyte) by stepping the potential of a Pt disk working electrode between potentials sufficient to form the radical anionic and cationic species. The relative amount of light produced during the anodic and cathodic pulses was dependent on the potential limits and pulse duration. ECL was also generated in the presence of coreactants, i.e., with tri-n-propylamine upon stepping the potential sufficiently positive to form the deprotonated tri-n-propylamine radical and the cationic rhenium(II) species Re II (L)(CO) 3 Cl + . When S 2 O 8 2was present in solution, ECL was also observed for all of the complexes upon stepping to potentials sufficient to form (Re I (L)(CO) 3 Cl)and the strong oxidant SO 4 •-. In most cases, the ECL spectrum was identical to the photoluminescence spectrum, indicating that the chemical reactions following electrochemical oxidation or reduction form the same metal-to-ligand charge-transfer (MLCT) excited states that are generated in the photoluminescence experiments.The photophysical properties of rhenium tricarbonyls containing bidentate polypyridyl ligands have been extensively studied. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Many exhibit strong photoluminescence in solution, suggesting they may be capable of electrogenerated chemiluminescence (ECL). These Re complexes are related to other d 6 transition metal systems such as the Os II and Ru II tris-diimine systems, which themselves are ECL emitting species. [15][16][17][18][19][20][21][22] These considerations and an earlier ECL study of Re phenanthroline complexes 2 prompted us to investigate the electrochemical properties of these complexes in more detail and to examine whether they can be used for the production of ECL.Complexes of the type Re(L)(CO) 3 Cl (where L is 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), or a methyl-substituted derivative, Figure 1) were chosen for this study in part due to the similarity of Re I and Ru II . With O h symmetry, both Re I and Ru II