Toward Silicon-Matched Singlet Fission: Energy-Level Modifications Through Steric Twisting of Organic Semiconductors

Singlet fission (SF) is a potential avenue for augmenting the performance of silicon photovoltaics, but the scarcity of SF materials energy-matched to silicon represents a barrier to the commercial realization of this technology. In this work, a molecular engineering approach is described to increase the energy of the S1 and T1 energy levels of diketopyrrolopyrrole derivatives such that the energy-level requirements for exothermic SF and energy-transfer to silicon are met. Time-resolved photoluminescence studies show that the silicon-matched materials are SF active in the solid state, forming a correlated triplet pair 1(TT) – a crucial intermediate in the SF process – as observed through Herzberg-Teller emission from 1(TT) at both 77 K and room temperature. Transient electron paramagnetic resonance studies show that the correlated triplet pair does not readily separate into the unbound triplets, which is a requirement for energy harvesting by silicon. The fact that the triplet pair do not separate into free triplets is attributed to the intermolecular crystal packing within the thin films. Nevertheless, these results demonstrate a promising route for energy-tuning silicon-matched SF materials

Quantification of energy transfer in bimetallic Pt(ii)–Ln(iii) complexes featuring an N^C^N-cyclometallating ligand

Cyclometallated Pt(II) complexes with arylpolypyridyl ligands have impressive photophysical properties (high quantum yields, long lifetimes and tuneable emission) which can be readily tuned by modification of the organic ligand. Despite this, few examples of cyclometallated Pt(II) complexes as sensitisers for Ln(III) emission have been reported. Herein, we report the photophysical properties for a series of bimetallic complexes incorporating an N^C^N-coordinated Pt(II) bearing an alkynyl terpyridine as a metalloligand for a Ln(III) ion (where Ln = Nd, Gd, Er, Yb and Lu). Using a combination of steady state, time-resolved, and transient absorption experiments, the influence on the photophysical properties of the metalloligand exerted by the different Ln(III) cations has been investigated, together with the energy transfer efficiency from the metalloligand to the Ln(III) 4f* excited state

Sensitised lanthanide luminescence using a RuIIpolypyridyl functionalised dipicolinic acid chelate

A visible light absorbing [RuII(tpy)2]2+-type chromophore appended with a dipicolinic acid LnIIIchelator has been prepared and complexed with several differing lanthanide cations to form the corresponding heterobimetallic d-f assemblies. The subseqent solution speciation analysed by1H NMR spectroscopy revealed an unexpected decrease in the LnIIIchelate complex stability, in particular for the 1 : 3 complex, when compared to the parent dipicolinic acid. As a result, the desired Ln(ML)3complexes could not be isolated, and the 1 : 1 LnIII-ML complexes were instead characterised and investigated using steady state absorption and emission spectroscopy. Sensitised NIR emission from the YbIII, NdIIIand ErIIIcomplexes was observed upon1MLCT excitation of the RuIIbased metalloligand in the visible region atca.485 nm. Investigations using transient absorption spectroscopy revealed essentially quantitative intersystem crossing to form the3MLCT excited state, as expected, which then acts as the energy donor for the metalloligand based antennae effect, facilitating sensitisation efficiencies of 4.8, 17.0 and 37.4% respectively for the YbIII, ErIIIand NdIIIcations.</p

Synthesis and characterisation of new tripodal lanthanide complexes and the investigation of their optical and magnetic properties

This paper presents the synthesis of a tripodal ligand (H3L) via the Schiff base condensation of N,N-diethylsalicylaldehyde and tris(2-aminoethyl)amine. The neutral complexes of type [EuL], [GdL] and [DyL] were synthesized and characterized by FT-IR, SEM-EDS, PXRD, single crystal X-ray diffraction, CHN analysis and high resolution ESI-MS. X-ray crystallographic studies demonstrated that the heptadentate ligand incorporating a cavity pre-organized by hydrogen bonding binds the Ln(iii) ions to yield a face capped octahedral coordination geometry with three-fold symmetry. Photoluminescence studies show a typical Ln(iii) absorption character for the three complexes, with [EuL] demonstrating considerably stronger lanthanide-based luminescence peaks, and a Eu(iii) centered luminescence lifetime of 0.144 + 0.01 ms. Temperature/field-dependent DC and temperature/frequency-dependent AC magnetic measurements carried out for the Dy(iii) complex indicated obvious magnetic anisotropy and suggested slow relaxation behaviour with considerable quantum tunnelling of the magnetization contribution