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Facile tuning of the aggregation-induced emission wavelength in a common framework of a cyclometalated iridium(III) complex: micellar encapsulated probe in cellular imaging

A simple synthetic protocol involving two steps was developed for the syntheses of a series of monocyclometalated iridium(III) complexes. Initially, an intermediate, [IrHCl[(o-C6H3X)P(Ar)x−(PArxRy)2] [A (i, j, k, l)], six-coordinated iridium(III) complex involving a 4-membered chelate was isolated. Then, it was transformed into a monocyclometalated iridium(III) complex, [(C^N)Ir(PArx−1Ry)2(Cl(H)] (1–12), by the replacement of the 4-membered chelates with 5-membered cyclometalates. The intermediates and the complexes were structurally characterized by FTIR, 1H, 13C and 31P NMR spectroscopies. Octahedral coordination for Ir(III) in 2, 8 and 9 was established by single crystal X-ray diffraction. Photo-physical experiments and quantum chemical calculations revealed a mixed LC/MLCT/LLCT nature for the lowest excited states of all these complexes that emit bright light in the solid state. Fine tuning of the emission wavelength throughout the visible range was achieved by suitable combinations of chromophoric cyclometalates and non-chromophoric aryl phosphine ligands. More interestingly, all the studied complexes were found to be aggregation-induced emission (AIE) active. One of these AIE active materials (6) was encapsulated inside polymeric micelles that inhibit the macroscopic precipitation of the aggregated complex, <200 nm water-soluble particle exhibiting a strong emission. These colloidal luminescent particles were used as a potential non-toxic bio-imaging probe.

‘Aggregation induced emission’ active iridium(III) complexes with applications in mitochondrial staining

Two new bis-cyclometalated iridium(III) complexes, [Ir(F2ppy)2(L)] and [Ir(ppy)2(L)], where F2ppy = 2-(2′,4′-difluoro)phenylpyridine, ppy = 2-phenylpyridine and L = 1,2-((pyridin-2-ylimino)methyl)phenol, have been designed and synthesized by a convenient route. We have univocally characterized their structure by 1H NMR, 19F NMR, HRMS and SXRD. Both complexes exhibit strong ‘Aggregation Induced Emission (AIE)’ activity, which has been investigated using spectroscopy measurements, ab initio quantum chemical calculations and by analysing their crystal packing. One of the complexes has been shown to have a potential application as a non-toxic bio-imaging probe for mitochondrial staining.

Dual emission and multi-stimuli-response in iridium(III) complexes with aggregation-induced enhanced emission: applications for quantitative CO2 detection

Four new Ir(III) complexes with the general formula [IrHCl(C^N)(PPh3)2] containing different conjugated Schiff base ligands (C^N) have been synthesized and characterized by 1H, 13C, and 31P NMR, HRMS, and IR spectra and one of them by single crystal X-ray diffraction. Their photophysical properties in solution and in the solid state have been analyzed and three main practical results have been obtained: (i) a dual fluorescent and phosphorescent emissive complex in solution, (ii) successful acid/base sensing in the solid state and (iii) quantitative CO2 detection. Quantum chemical calculations have been employed to assign the character of the lowest excited states. A plausible explanation for the observed aggregation induced enhanced emission (AIEE) is given, based on the restriction of intramolecular motions due to the effect of intermolecular C–H⋯π and C–H⋯Cl type interactions upon aggregation.

Optical properties of 4-bromobenzaldehyde derivatives in chloroform solution.

In this work we give a deeper insight into the electronic structure of a series of purely organic molecules that were recently employed as building blocks in crystals with very efficient phosphorescent emission. With this purpose, the low-lying excited states of a series of 4-bromobenzaldehyde derivatives in chloroform solution are explored by means of time-dependent density functional theory (TDDFT) calculations, together with the absorption, fluorescence, and phosphorescence experimental spectra. The optical properties of the studied molecular models are extensively discussed, in terms of the frontier molecular orbitals involved in the relevant electronic transitions, the recorded and simulated absorption profiles, and the molecular geometries and transition energies of the emitting states. The calculations eventually help in the assignment of the character of the lowest lying singlet and triplet emitting states for these compounds.

Computational comparison of CPDT to other conjugated linkers in triarylamine-based organic dyes.

The use of the cyclopentadithiophene (cpdt) fragment to chemically link electron donor and acceptor groups has become a rather common procedure to design new organic dyes with enhanced light harvesting properties. The photo-to-current efficiencies obtained by sensitized solar cells with dyes incorporating the cpdt moiety are commonly improved with respect to other similar π-fragments as separators. In many cases, the advantages of cpdt can be related to the larger extinction coefficients obtained. In this work we perform a detailed computational study of triarylamine-based organic dyes with the cyanoacrylic acid as the acceptor group and considering a variety of conjugated linkers with cpdt as the reference case. The influence of slightly different linkers and donor groups in the computed excitation energies and oscillator strengths is discussed by means of molecular geometries and frontier orbitals. The structural characteristics imposed by cpdt compared to similar conjugated bridges are responsible for its larger computed oscillator strengths. The insertion of an ethylene unit between the donor group and the linker systematically reduces the energy gap to the first excited singlet state and yields larger oscillator strengths of the optical transition. These results could be very helpful in the quest of new organic dyes with improved properties as sensitizers in Grätzel cells.