Search

Multi-branched molecules have recently demonstrated interesting behaviour as charge-transporting materials within the fields of perovskite solar cells (PSCs). For this reason, extended triarylamine dendrons have been grafted onto a pillar[5]arene core to generate dendrimer-like compounds, which have been used as hole-transporting materials (HTMs) for PSCs. The performances of the solar cells containing these novel compounds have been extensively investigated. Interestingly, a positive dendritic effect has been evidenced as the hole transporting properties are improved when going from the first to the second-generation compound. The stability of the devices based on the best performing pillar[5]arene material has been also evaluated in a high-throughput ageing setup for 500 h at high temperature. When compared to reference devices prepared from spiro-OMeTAD, the behaviour is similar. An analysis of the economic advantages arising from the use of the pillar[5]arene-based material revealed however that our pillar[5]arene-based material is cheaper than the reference.

Dinuclear copper(I) complexes have been prepared starting from bis(diphenylphosphanyl)acetylene (dppa), [Cu(CH3CN)(4)](BF4) and various 1,10-phenanthroline ligands (NN), namely 1,10-phenanthroline (phen), neocuproine (dmp), bathophenanthroline (Bphen), bathocuproine (Bdmp) and 2-phenyl-1,10-phenanthroline (mpp). The resulting [Cu-2(mu-dppa)(2)(NN)(2)](BF4)(2) complexes have been thus obtained in excellent yields (88 to 94 %). X-ray crystal structure analysis of four complexes revealed that the 10-membered dimetallacycle adopts a chair-like conformation in the solid state. Detailed variable temperature NMR investigations have evidenced dynamic coordination/decoordination of the NN ligands as well as ligand exchange reactions. At high temperature (100 degrees C), entropic effects tend to destabilize the dinuclear heteroleptic complexes. As a result, homoleptic mononuclear complexes, i.e. [Cu(NN)(2)](+) and undefined dppa copper(I) complexes, start to appear in solution. In contrast, the heteroleptic coordination scenario is almost exclusively favored at lower temperatures. For most of the dinuclear complexes, the 10-membered dimetallacycle remains flexible and chair-to-chair interconversion occurs faster than the NMR timescale even at -70 degrees C. In the particular case of the mpp derivative, the bulky phenyl substituent prevents the isomerization of the metallacycle and thus contributes to rigidify the structure. This rigidification has a dramatic effect on the emission properties of this particular compound. The emission quantum yield of [Cu-2(mu-dppa)(2)(mpp)(2)](BF4)(2) is effectively one order of magnitude higher when compared to all the other complexes in this series (20 % vs. 0.3-1.7 % in the solid state).

The electronic and structural properties of ten heteroleptic [Cu(NN)(PP)]+ complexes have been investigated. NN indicates 1,10-phenanthroline (phen) or 4,7-diphenyl-1,10-phenanthroline (Bphen); each of these ligands is combined with five PP bis-phosphine chelators, i.e., bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-bis(diphenylphosphino)propane (dppp), 1,2-bis(diphenylphosphino)benzene (dppb), and bis[(2-diphenylphosphino)phenyl] ether (POP). All complexes are mononuclear, apart from those based on dppm, which are dinuclear. Experimental data - also taken from the literature and including electrochemical properties, X-ray crystal structures, UV-vis absorption spectra in CH2Cl2, luminescence spectra and lifetimes in solution, in PMMA, and as powders - have been rationalized with the support of density functional theory calculations. Temperature dependent studies (78-358 K) have been performed for selected complexes to assess thermally activated delayed fluorescence. The main findings are (i) dependence of the ground-state geometry on the crystallization conditions, with the same complex often yielding different crystal structures; (ii) simple model compounds with imposed C2v symmetry ([Cu(phen)(PX3)2]+ X = H or CH3) are capable of modeling structural parameters as a function of the P-Cu-P bite angle, which plays a key role in dictating the overall structure of [Cu(NN)(PP)]+ complexes; (iii) as the P-Cu-P angle increases, the energy of the metal-to-ligand charge transfer absorption bands linearly increases; (iv) the former correlation does not hold for emission spectra, which are red-shifted for the weaker luminophores; (v) the larger the number of intramolecular π-interactions within the complex in the ground state, the higher the luminescence quantum yield, underpinning a geometry locking effect that limits the structural flattening of the excited state. This work provides a general framework to rationalize the structure-property relationships of [Cu(NN)(PP)]+, a class of compounds of increasing relevance for electroluminescent devices, photoredox catalysis, and solar-to-fuels conversion, which so far have been investigated in an unsystematic fashion, eluding a comprehensive understanding. © Copyright 2018 American Chemical Society.