Electrochemistry and electrogenerated chemiluminescence of a novel donor-acceptor FPhSPFN red fluorophore

We report here the electrogenerated chemiluminescence (ECL) of a red fluorophore diphenylaminospirobifluorenylfumaronitrile (FPhSPFN). FPhSPFN contains two diphenylamino groups as strong electron donors at the ends linked through a nonplanar bulky spirobifluorene linker to a common fumaronitrile group as a strong electron acceptor. The cyclic voltammetry of this compound shows two one-electron transfer reduction waves and one single overall two-electron oxidation wave consisting of closely spaced waves with a peak separation of 63 mV. Chronoamperometry with an ultramicroelectrode (UME) confirmed that each reduction wave involves a 1e transfer and that the oxidation wave contains an overall 2e transfer. The first reduction wave is Nernstian, E^o _1,red =-1.09 V versus SCE, and the second reduction wave, E ^o_2,red =-1.50 V versus SCE, produces a film on the electrode. By comparison to a digital simulation, the oxidation is assigned to two reversible, closely spaced, one-electron processes for oxidation with E ^o_1,ox = 1.05 V and E^o_2,ox = 1.11 V versus SCE. A large wavelength shift (∼35 nm) was observed in ECL as compared to photoluminescence (PL). The ECL spectrum showed a maximum emission at 708 nm with a red-shifted shoulder at around 750 nm. ECL was studied in mixtures of benzene/acetonitrile at different composition ratios; an increase in the ratio of the ECL intensity of the shoulder with respect to the main peak emission was observed with increasing solvent polarity. ECL generated with BPO as a coreactant also showed the red-shifted shoulder at the same ratio as that with annihilation.