Redox-driven photoselective self-assembly

Abstract

Self-assembly via non-covalent interactions is key to constructing complex architectures with advanced functionalities. A noncovalent synthetic chemistry approach, akin to organic chemistry, allows stepwise construction with enhanced control. Here, we explore this by coupling Pt(II) complex self-assembly with a redox reaction. Oxidation to Pt(IV) creates a non-emissive monomer that, upon reduction to Pt(II), forms luminescent gels with unique kinetic and thermodynamic pathways. UV irradiation induces Pt(IV) reduction, generating supramolecular fibers with Pt∙∙∙Pt interactions, enhancing photophysical properties and enabling visible light absorption up to 550 nm. This allows photoselective growth, where fibers convert surrounding Pt(IV) to Pt(II), promoting growth over nucleation, as observed via real-time fluorescence microscopy.

Fig. 1. Self-assembly pathway selection by photo or chemical reduction.

Reaction scheme, operating conditions of the redox process under analysis, and aggregation states achievable directly from compound 1 or through the reduction of compound 2.

Fig. 2. Photophysical properties of gels and disrupted gels.

a Normalized UV-Vis of G1,2 (up) and D1,2 (down). b Normalized emission spectrum of G1,2 (up) and D1,2 (down). Concentration of samples for both a and b: 2.6*10⁻²M in THF (blue line) and ACN (orange line). c Fluorescence microscope pictures of aggregates derived from a drop cast of G2 (up), and D2 (down) at λ = 385 nm of irradiation.

Fig. 3. Photoreduction of Pt(IV) species observed via fluorescence microscopy.

a Snapshot of Supplementary Movie 2; photoreduction of 2 at 10⁻³ M in ACN/H₂O (2:1 ratio); light irradiation at λ = 385 nm, magnification ×20. b Snapshot of a spot previously irradiated at 385 nm (×10 magnification, λ = 555 nm). c Circle drawn with a deuterium lamp equipped with a beam-shaping mask using a solution 2 in THF/H₂O (1:1 ratio) at 2.6*10⁻²M concentration.

Fig. 4. Selective elongation of Pt(II) fibers.

a Pathway scheme of the selective elongation of Pt(II) fibers under visible light irradiation (λ = 555 nm). Dispersion of aggregates drop casted into a 10⁻³M solution of 2 in a 2:1 ACN/H₂O solvent system. b UV-Vis spectrum of 2 in ACN at 10⁻⁴M concentration, onset at λ = 400 nm. c Excitation spectrum of aggregated form of 1 obtained by photoreduction of 2 at 10⁻³M concentration in ACN/H₂O 1:1, onset at λ = 550 nm.

Fig. 5. Quantitative analysis and EDX of Pt(II) fibers selective elongation.

a Quantitative analysis of selective elongation of Pt(II) aggregates via UV–Vis monitoring the Pt(IV) depletion over irradiation with UV light (λ = 403 nm) and green light (λ = 517 nm); initial condition: compound 2 at 2*10⁻³M concentration in a 2:1 ACN/H₂O solvent mixture (1 mm cuvette). b SEM analysis of the Pt(II) fibers and residual Pt(IV) mixture obtained at the end of the second run of the selective aggregates elongation experiment (1 cm cuvette, same solvent and initial concentration as picture a). c EDX mapping of Pt in the same spot of the SEM analysis. d EDX mapping of Cl in the same spot of the SEM analysis.