Spectroscopic, electrochemical and computational study of Pt–diimine–dithiolene complexes: rationalising the properties of solar cell dyes

Abstract

A series of [Pt(ii)(diimine)(dithiolate)] complexes of general formula [Pt{X,X'-(CO(2)R)(2)-bpy}(mnt)] (where X = 3, 4 or 5; R = H or Et, bpy = 2,2'-bipyridyl and mnt = maleonitriledithiolate), have been spectroscopically, electrochemically and computationally characterised and compared with the precursors [Pt{X,X'-(CO(2)R)(2)-bpy}Cl(2)] and X,X'-(CO(2)R)(2)-bpy. The study includes cyclic voltammetry, in situ EPR spectroelectrochemical studies of fluid solution and frozen solution samples, UV/Vis/NIR spectroelectrochemistry, hyrid DFT and TD-DFT calculations. The effect of changing the position of the bpy substituents from 3,3' to 4,4' and 5,5' is discussed with reference to electronic changes seen within the different members of the family of molecules. The performance of the mnt complexes in dye-sensitised solar cells has been previously described and the superior performance of [Pt{3,3'-(CO(2)R)(2)-bpy}(mnt)] is now explained in terms of decreased electronic delocalisation through twisting of the bipyridyl ligand as supported by the EPR and computational results.

Synthesis and Structural Features of [4,4′-Diisopropoxyester-2,2′-bipyridine], [Dichloro(4,4′-diisopropoxyester-2,2′-bi-pyridine)-platinum(ii)] and Its Dichloromethane Solvated Pseudo-Polymorph: Versatile Supramolecular Interactions

“…The presence of the solvent molecules completely changes the crystal packing of (3) from that in (2). Indeed, the core molecules in (3) form Pt2ÁÁÁPt1ÁÁÁPt1AÁÁÁPt2A intermolecular contacts with alternating distances 3.501, 3.431, 3.501 Å , respectively, forming infinite chains along the b axis (Fig.…”

“…4). These contacts manifest weak metallophilic (platinophilic in particular) pairwise interactions as the second type of supramolecular interactions in (2). In addition to platinum atom contacts, weak intermolecular C-HÁÁÁO hydrogen bonds link molecules A and B with almost orthogonal orientation as dimers ( Fig.…”

“…The nature of this low energy absorption characterized as a charge transfer to the diimine makes these systems attractive for use as chromophores in molecular assemblies for photo-induced charge separation in dye sensitized solar cells [2][3][4] or, more recently by our research team, small-molecule organic photoltaics (OPVs) [5]. The excited state of many of these systems has been extensively studied as a result [2][3][4][5][6][7]. Although the photophysical properties for many systems are reported, crystallographic studies remain starkly underrepresented versus the number of synthesized complexes.…”

First-principles study of nickel complex with 1,3-dithiole-2-thione-4,5-dithiolate ligands as model photosensitizers

“…In a later study [17] the superior performance of the 3,3'-bipyridyl complex was rationalized by using density functional theory calculations based on a hybrid functional that suggested that the longer-lived charge-separated state for this complex on TiO 2 was related to the non-planar geometry of the complex, reducing the electronic coupling between ligands. Lazarides et al [18] have attempted to increase the light absorption properties of Pt(II)(diimine)(dithiolate) chromophores by combining them with boron-dipyrromethene, a strongly absorbing dye, in a dual chromophore system.…”

“…In this regard, square-planar complexes with sulfur-containing ligands that absorb in the near infrared region (NIR) of the spectrum have attracted special interest and have been examined both experimentally and theoretically [12,15,16,17,18,19].…”