A Combined Experimental and Theoretical Study into the Excited States of Luminescent Platinum Complexes

Abstract

Luminescent transition metal complexes have attracted much attention in recent years due to their potential as phosphors in organic light-emitting devices, their use in sensory systems and their applications in bioimaging. It is often desirable to predict the photophysical properties of such compounds to allow tailored design, accentuating certain characteristics. This combined experimental and theoretical study of the excited states of platinum complexes outlines synthesis, photophysical measurements and theoretical consideration of some such compounds, giving insight into the theoretical techniques applied.

Reproduction of absorption spectra is described for a series of previously reported Pt(II) complexes, using different basis sets, functionals and solvent models, the techniques then applied to a novel set of related Pt(IV) complexes. Understanding of these parameters was then used for more complicated modelling of the emissive process in thiolate-substituted derivatives of Pt(dpyb)Cl. These were studied experimentally and theoretically, showing a change in excitation character upon coordination of the thiolate ligand. TD-DFT showed the importance of modelling solvent for the prediction of the correct excitation character, alongside a consideration of techniques and mathematical parameters for the correct calculation of emission energies.

Bis-imine, bis-ketimine and bis-oxime ligands have been synthesised by Schiff base condensation chemistry and their corresponding N∧C∧N-coordinated Pt(II) complexes prepared. A wide range in quantum yields was observed and attributed to varying rates of non-radiative decay. Consideration of the S0 and T1 geometries by DFT and their distortion relative to one another showed the origin of this decay. Methyl-substituted benzenes were investigated for similar properties. Those derivatives for which the calculations predict significant distortion do show emission properties typical of triplet state distortion. However, due to “triplet instabilities”, TDA geometries appear to be more reliable than those calculated by DFT, showing better consistency with the experimental trends.

Techniques described above were also applied to other classes of Pt(II) complexes. The rate of radiative decay was considered for these compounds by taking into account both the orbital overlap and the degree to which the metal atom was involved in the excitation.