The Study Of Electrochemiluminescencce Of Ionic Iridium Complexes

Iridium complexes have been the subject of a growing interest to wide scientific community due to their high photoluminescence efficiency, a diverse range of wavelengths and stable electrochemical property. Iridium complexes were used to prepare sensors by many people. But most of the iridium complexes were neutral iridium complexes, the electrochemiluminescent(ECL) sensor made by ionic iridium complexes were reported rarely. Because of the ion characteristic of ionic iridium complexes, the amount of ionic iridium complexes adsorbed on the electrode by ion exchange was larger than neutral iridium complexes. Moreover the synthesis condition of ionic iridium complexes was mild and synthesis method was simple, which inspired us to study new ionic iridium complexes. The immbolization method of iridium complexes would influence the conductivity, sensitivity and selectivity of ECL sensor, so it’s important to choose appropriate immbolization methods. In this paper, the synthesis of ionic iridium complexes with high photoluminescence efficiency and the immobilization methods were studied to prepare highly sensitive and stable ECL sensors. Based on the density factional theory calculation, the effect of the structure of ionic iridium complexes on the electrochemical and ECL properties was studied preliminarily. It will provide theoretical guidance for the synthesis of ionic iridium complexes with high photoluminescence efficiency.The main results of the paper were given as follows:1. The six iridium complex, including neutral iridium and ionic iridium, were studied by DFT theory. They were [(bpq)2Ir(bpy)]+PF6-, [(bpq-OCH3)2Ir(bpy)]+PF6-, [(bpq-NO2)2Ir(bpy)]+PF6-, [(bpq)2Ir(phen)]+PF6-,(pq)2Ir(acac) and(pq)2Ir(N-phma), where bpq is 6-methyl-2,4-diphenyl quinolone anion, bpy is 2,2’-bipyridine, phen is phenanthroline anion, pq is phenylquinoline anion and acac is acetylacetone anion, phma is phenylmethacrylamide. The frontier orbital composition results showed that the relaxation of the excited state for the neutral iridium complexes were mainly attributed to the transition between [dÏ€(Ir)â†'Ï€*C∧N] metal-to-ligand charge-transfer(3MLCT) and 3[Ï€C∧Nâ†'Ï€*C∧N] ligand-to-ligand charge-transfer(LLCT), whereas for the ionic iridium complexes, the relaxation can be attributed to the transition between the special [dÏ€(Ir)â†'Ï€*N∧N] 3MLCT states and 3[Ï€C∧Nâ†'Ï€*N∧N] LLCT. The HOMO energies of [(bpq)2Ir(bpy)]+PF6- and [(bpq-OCH3)2Ir(bpy)]+PF6- were low, so their oxidation potentials were small. The ionic iridium complexes(bpq)2Ir(bpy)+PF6- and [(bpq-OCH3)2Ir(bpy)]+PF6- were synthesized and structurally characterized by X-ray crystallography, nuclear magnetic resonance. Their maximum emission wavelengths were at about 575 nm. The photoluminescence quantum yields(ΦPL) were 0.214, 0.209, respectively for [(bpq)2Ir(bpy)]+PF6- and [(bpq-OCH3)2Ir(bpy)]+PF6-, which were markedly higher than the reference material [Ru(bpy)3]2+(ΦPL=0.098) in CH3 CN under deoxygenated condition.2. Based on the derivatization of [(bpq-OCH3)2Ir(bpy)]+PF6-, a novel ionic iridium complex, [(bpq-OCH3)2Ir(dcbpy)]+PF6-, where dcbpy is 4,4’-dicarboxyl-2,2’-dipyridine, was synthesized and structurally characterized by nuclear magnetic resonance and infrared spectroscopy. A new method based on S-Au covalent bonding was proposed to make ECL sensor. The results showed that the modified film made by self- assembly was well ordered and stable, and the conductivity of GCE was improved by Au NPs. The ECL properties were studied and the results showed that the ECL sensor exhibited high sensitivity and good stability against the coreactant of 2-(dibutylamino) ethanol(DBAE). The linear equation was log(IECL) = 0.2285 log C + 3.391,r = 0.9918,and the detection limit was 3.04×10-9 mol/L. The ECL sensor was stably used in two weeks.3. In order to improve the selectivity of ECL sensor, ECL and the molecular imprinting technique were combinated to prepare MIP-ECL sensor and we proposed a new immobilization method. First, the composite solution containing cation exchanger Nafion, multi-walled carbon nanotubes and ionic iridium complex was coated on the GCE to make ECL sensor. The molecularly imprinted(MIP) film was modified on the ECL sensor by electro-polymerization to get MIP-ECL sensor. The study showed that the MIP film was formed rapidly and film thickness was readily controlled by the selection of the electro-polymerization time. The as-prepared MIP-ECL sensor exhibited high sensitivity and good selectivity against the codeine, the linear range from 1.0×10-11 to 5.0×10-9 mol/L was obtained. The linear equation was IECL = 11.21 log C + 127.98, r = 0.9962,and the detection limit was 9.23×10-12 mol/L(S/N = 3).