Engineering Tunable Single and Dual Optical Emission from Ru(II)-Polypyridyl Complexes through Excited State Design

Excited state design is an efficient approach towards new applications in molecular electronics spanning solar cells, artificial photosynthesis and biomedical diagnostics. Ruthenium (II)-polypiridyl based complexes are an example of molecular building blocks with tunable single and dual wavelength emission which can be controlled by excited state engineering via selective ligand modification. Here we investigate three new heteroleptic [Ru(bpy)2X]+ complex ions, where X represents pyridinyl or pyrazinyl derivatives of diazolates, providing tunable emission in the visible and infrared region. The dual emission is shown to arise from the presence of two excited states consisting of a triplet metal-to-ligand charge transfer state localized on a bipyridine ligand - 3MLCT (bpy), and either a state that is entirely localized on the X ligand or is partially delocalized also spanning part of the bipyridine ligands - 3MLCT(X). By a suitable choice of the X ligand, emission from 3MLCT(bpy) and 3MLCT (X) states can be rationally varied between 743 - 865 nm and from 555 - 679 nm, respectively. An increase in the nitrogen content of the six-membered ring of the X ligand results in a blueshift of the 3MLCT(bpy) emission but a redshift for the 3MLCT (X) emission. The wavelength difference between 3MLCT(bpy) and 3MLCT (X) emissions that can be tuned from 84–310 nm and is proportional to the difference in LUMOs energies (reduction potentials) of the isolated ligands. Our study provides key information towards new routes for the design of optically active dual wavelength molecular emitters

The Role of Substituent Effects in Tuning Metallophilic Interactions and Emission Energy of Bis-4-(2-pyridyl)-1,2,3-triazolatoplatinum(II) Complexes

The photoluminescence spectra of a series of 5-substituted pyridyl-1,2,3-triazolato PtII homoleptic complexes show weak emission tunability (ranging from λ=397-408 nm) in dilute (10-6 M) ethanolic solutions at the monomer level and strong tunability in concentrated solutions (10-4 M) and thin films (ranging from λ=487-625 nm) from dimeric excited states (excimers). The results of density functional calculations (PBE0) attribute this "turn-on" sensitivity and intensity in the excimer to strong Pt-Pt metallophilic interactions and a change in the excited-state character from singlet metal-to-ligand charge transfer (1MLCT) to singlet metal-metal-to-ligand charge transfer (1MMLCT) emissions in agreement with lifetime measurements. Turn-on tunability: A series of bis-4-(2-pyridyl)-1,2,3-triazolatoplatinum(II) complexes display variable emission tunability. At low concentration, the emission can be tuned only slightly by changing the nature of the substituent but at higher concentrations tunability is enhanced. This "turn-on" sensitivity in the excimeric emission is attributed to strong Pt-Pt metallophilic interactions and a change in the excited-state character

Formation and photophysics of a stable concave-convex supramolecular complex of C-60 and a substituted s-triazine derivative

Spectroscopic, electrochemical and computational data show that C-60 and a highly phenylated s-triazine derivative form a stable supramolecular complex at micromolar concentrations in solution at ambient temperatures, due to strong van der Waals attraction between their complementary surfaces

Phase Change Transformations with Dynamically Addressable Aminal Metallogels

Dynamic polymers assembled through hemiaminal and aminal functionalities reversibly fragment upon binding to trivalent metals. Gels produced with these dynamic polymers are broken down to liquids after the addition of metal salts. Nuclear magnetic resonance spectroscopy studies and density functional theory calculations of intermediates reveal that the presence of these metals causes shifts in the energetic landscape of the intermediates in the condensation pathway to render stable nonequilibrium products. These species remain stable in the liquid phase at room temperature but convert to gels upon heating. With thermal activation, the fragmented ligands transform catalytically into closed-ring hexahydrotriazine products, which are macroscopically observable as new gels with distinct physical properties. The interplay between equilibrium and nonequilibrium gels and liquids and the ligands responsible for these transformations has been observed rheologically, giving controlled gel times dictated by the thermodynamics and kinetics of the system. This constitutionally dynamic macromolecular system offers the possibility of harnessing an equilibrium/nonequilibrium system in tandem with its inherent self-healing properties and triggered release functionality