Electrogenerated Chemiluminescence. 61. Near-IR Electrogenerated Chemiluminescence, Electrochemistry, and Spectroscopic Properties of a Heptamethine Cyanine Dye in MeCN


The oxidation of the heptamethine cyanine dye 2-[4′-chloro-7′-(1″-methyl-3″,3″-dimethylindolin- 2″-ylidene)-3′,5′-(propane-1‴,3‴-diyl)-1′, 3′,5′-heptatrien- 1′-yl]-1-methyl-3,3-dimethylindolinium cation (HMC+) in the presence of tri-n-propylamine (TPrA) at +0.7 V vs SCE in MeCN produces near-IR electrogenerated chemiluminescence (ECL) with an emission maximum at about 805 nm and a relative ECL quantum efficiency of 0.21 vs Ru(bpy)32+ (bpy = 2,2′-bipyridine) with TPrA in MeCN as a standard. The ECL emission spectra are identical to the photoluminescence spectra. The concentration dependence of the ECL is attributed to both self-absorption and competition by radical dimerization reactions. An oxidative-reduction mechanism for excited state formation is proposed and is compared to the Ru(bpy)32+/TPrA reference system. Digital simulation was employed to examine the kinetics of the homogeneous redox reaction between TPrA and HMC+. The rate constant for the catalytic reaction is >2000 M-1 s-1, and the lower limit for proton transfer is 107 M-1 s-1. Molecular mechanics calculations were used to determine the most stable configuration for the HMC+ molecule.

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Analytical Chemistry