The syntheses of five homoleptic copper(I) complexes [CuL₂][PF₆] are described in which L is a 4,4′-di(4-bromophenyl)-6,6′-dialkyl-2,2′-bipyridine ligand (compounds 1–4 with methyl, ⁿbutyl, ^isobutyl and hexyl substituents, respectively) or 4,4′-di(4-bromophenyl)-6,6′-diphenyl-2,2′-bipyridine (5). The new ligands 2–5 and copper(I) complexes [CuL₂][PF₆] (L = 1–5) have been fully characterized. The single crystal structures of 2{[Cu(1)₂][PF₆]}·3Me₂CO, [Cu(2)₂][PF₆], 2{[Cu(3)₂][PF₆]}·Et₂O and [Cu(5)₂][PF₆]·CH₂Cl₂ have been determined. The first three structures show similar distorted tetrahedral environments for the Cu⁺ ions with angles between the least squares planes of the bpy domains of 85.6, 86.4 and 82.9°, respectively; in contrast, the Cu⁺ ion in [Cu(5)₂][PF₆]·CH₂Cl₂ is in a flattened coordinate environment due to intra-cation face-to-face π-interactions. The solution absorption spectra of the complexes with ligands 1–4 are virtually identical with an MLCT band with values of λ_max = 481–488 nm. In contrast, the absorption spectrum of [Cu(5)₂][PF₆] shows two broad bands in the visible region. Cyclic voltammetric data show that oxidation of the copper(I) centre occurs at a more positive potential in [Cu(2)₂][PF₆], [Cu(3)₂][PF₆] and [Cu(4)₂][PF₆] than in [Cu(1)₂][PF₆] or [Cu(5)₂][PF₆] with the latter being oxidized at the lowest potential. The complexes have been used to prepare dye-sensitized solar cells (DSCs) incorporating heteroleptic dyes of type [Cu(L)(L_anchor)]⁺ where L is 1–5 and L_anchor is a 6,6′-dimethyl-2,2′-bipyridine functionalized in the 4- and 4′-positions with phosphonic acid groups with (L_anchor = 7) and without (L_anchor = 6) a spacer between the metal-binding and anchoring domains. The presence of the spacer results in enhanced performances of the dyes, and the highest energy conversion efficiencies are observed for the dyes [Cu(3)(7)]⁺ (η = 2.43% compared to 5.96% for standard dye N719) and [Cu(5)(7)]⁺ (η = 2.89% compared to 5.96% for N719). Measurements taken periodically over the course of a week indicate that the cells undergo a ripening process (most clearly seen for [Cu(5)(6)]⁺ and [Cu(5)(7)]⁺) before their optimum performances are achieved. IPCE (EQE) data are presented and confirm that, although the photo-to-current conversions are promising (37–49% for λ_max ≈ 480 nm), the copper(I) dyes do not realize the broad spectral response exhibited by N719.

Ligands containing first and second generation hole-transport triphenylamino-dendrons have been evaluated as ancillary ligands in copper(I) DSCs yielding an optimal efficiency of 3.77% in unmasked cells. The effects of masking the DSCs on measured parameters are discussed.

A series of four heterocyclic dimers has been synthesized, with twisted geometries imposed across the central linking bond by ortho‐alkoxy chains. These include two isomeric bicarbazoles, a bis(dibenzothiophene‐S,S‐dioxide) and a bis(thioxanthene‐S,S‐dioxide). Spectroscopic and electrochemical methods, supported by density functional theory, have given detailed insights into how para‐ vs. meta‐ vs. broken conjugation, and electron‐rich vs. electron‐poor heterocycles impact the HOMO–LUMO gap and singlet and triplet energies. Crucially for applications as OLED hosts, the triplet energy (E_T) of these molecules was found to vary significantly between dilute polymer films and neat films, related to conformational demands of the molecules in the solid state. One of the bicarbazole species shows a variation in E_T of 0.24 eV in the different media—sufficiently large to “make‐or‐break” an OLED device—with similar discrepancies found between neat films and frozen solution measurements of other previously reported OLED hosts. From consolidated optical and optoelectronic investigations of different host/dopant combinations, we identify that only the lower E_T values measured in neat films give a reliable indicator of host/guest compatibility. This work also provides new molecular design rules for obtaining very high E_T materials and controlling their HOMO and LUMO energies.

Homoconjugation occurs when two aromatic rings are separated by a single non-conjugated atom. This is demonstrated in triptycene by the through-space overlap of the π-clouds of the aryl fins and can be used to enhance optoelectronic properties.