Comprehensive Investigation of the Photophysical Properties of Alkynylcoumarin Gold(I) Complexes

Abstract

Six gold(I) complexes (R 3 P-Au-Coum) containing three different alkynylcoumarin chromophores (Coum) with different electron-donating and electron-withdrawing characteristics and two different water-soluble phosphanes (PR 3 = PTA (a) and DAPTA (b)) have been synthesized (1a,b, unsubstituted coumarin; 2a,b, 4-methyl substituted coumarin; 3a,b, 3-chloro and 4-methyl substituted coumarin). A comprehensive study of the photophysical properties of the R 3 P-Au-Coum, together with their propynyloxycoumarin precursors 1−3, was performed in solution at room and low temperatures. Spectral and photophysical characteristics of the R 3 P-Au-Coum essentially depend on the electronic characteristics of the propynyloxycoumarin ligand. The presence of the Au(I) atom was found to be responsible for an increase of the intersystem crossing, with triplet state quantum yield values, ϕ T , ranging from ∼0.05 to 0.35 and high coumarin phosphorescence quantum yield values for derivatives 1 and 2; fluorescence dominates the deactivation in derivatives 3. Efficient singlet oxygen photosensitization was observed for the new compounds 3a,b. From TDDFT calculations, the relevant HOMO and LUMO of the compounds, i.e., those involved in the transitions, are dominated by the frontier orbitals associated with the coumarin core. The Au(I)-phosphane structure introduces a new transition assigned to an intraligand transition involving the phosphane ligand, and π(CC) system, to the p orbitals of phosphorus and gold atoms.

Aggregation of gold(i) complexes: phosphorescence vs. singlet oxygen production

“…The singlet oxygen quantum yield production values, Φ Δ , (9–26%) (Table 3) obtained are moderate compared with other gold( i ) complexes found in the literature. 20–23 Interestingly, the neutral gold( i ) complexes that contains 4-ethynilaniline as a ligand ( 1–3 ) display higher values of singlet oxygen sensitization. This can be correlated with the more efficient phosphorescence emission and aggregation process.…”

“…The singlet oxygen quantum yield production values, Φ Δ , (9-26%) (Table 3) obtained are moderate compared with other gold(I) complexes found in the literature. [20][21][22][23] Interestingly, the neutral gold(I) complexes that…”

“…19 Among all the metals used in the literature for singlet oxygen production, gold(I) is scarcely explored and only a few examples have been reported in the literature in this field. [20][21][22][23] Supramolecular chemistry offers several advantages within this field. The majority of the published results use cavitands (such as curcubiturils, cyclodextrins or calixarenes) to encapsulate the photosensitizer in order to disrupt the aggregation process (aggregation-induced photo-deactivation) and enhance their singlet oxygen generation.…”

“…19 Among all the metals used in the literature for singlet oxygen production, gold( i ) is scarcely explored and only a few examples have been reported in the literature in this field. 20–23…”

Aggregation-Induced Emission with Alkynylcoumarin Dinuclear Gold(I) Complexes: Photophysical, Dynamic Light Scattering, and Time-Dependent Density Functional Theory Studies

“…27,29 This, in turn, facilitates access to excited triplet states by increasing the spin−orbit coupling (SOC), thus favoring the S 1 ∼∼→T 1 intersystem crossing pathway. 8,23,30,32 Inclusion of the phosphane ligands allows the introduction of complementary electronic properties, together with several different types of coordination geometries, in transition-metal centers, improving the predictable physical and chemical properties of these new complexes. 33−35 Additionally, gold(I) complexes can display dual luminescence at room temperature with emission efficiencies that depend significantly on the structure of the molecule.…”