Issue 39, 2022

Sterically demanding pyridine-quinoline anchoring ligands as building blocks for copper(i)-based dye-sensitized solar cell (DSSC) complexes

Abstract

The Pfitzinger condensation reaction was employed to synthesise N^N sterically demanding ligands bearing carboxylic acid anchoring groups, namely 2,2′-pyridyl-quinoline-4-carboxylic acid (pqca), 6′-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (6′-Mepqca), 8-methyl-2,2′-pyridyl-quinoline-4-carboxylic acid (8-Mepqca) and 8,6′-dimethyl-2,2′-pyridyl-quinoline-4-carboxylic acid (8,6′-Me2pqca). Preparation of the methyl ester analogues 6′-Mepqcame, 8-Mepqcame and 8,6′-Me2pqcame is also described. All ligands were fully characterised including the X-ray structures of pqca, 6′-Mepqca and 8-Mepqca. We also describe the synthesis and characterisation of seven homoleptic copper(I) complexes of the formula [Cu(N^N)2][PF6] (N^N = pqca (1), 6′-Mepqca (2), 8-Mepqca (3), 8,6′-Me2pqca (4), 6′-Mepqcame (6), 8-Mepqcame (7) and 8,6′-Me2pqcame (8)). Characterisation of the copper(I) complexes includes FT-IR, elemental analyses, multinuclear NMR spectroscopy, UV-vis spectroscopy, cyclic voltammetry, and a single-crystal X-ray diffraction study. The molecular structures of 1·DMSO, 2{2·Me2CO·0.5H2O}, 4, 6·CHCl3·0.13H2O, 2{7·C5H12}·CHCl3 and 8 have been determined, revealing that these complexes adopt a distorted tetrahedral geometry. These are the first crystallographically characterised examples of copper(I)-based coordination compounds incorporating the above mentioned N^N pyridyl-quinoline ligands. In solution, the new complexes are purple to red colored, while 2 displayed excellent stability in acetone at ambient temperature over a month. The absorption spectra of 1–8 display a main broad MLCT band with values of λmax at ∼530 nm and ε values ranging from 1800 to approximately 10 000 dm3 mol−1 cm−1. The photovoltaic performance of the prepared compounds was evaluated on mesoporous nanocrystalline TiO2 dye-sensitized solar cells (DSSCs), and compared with that of the [Cu(dmdcbpy)2][PF6] dye (dmdcbpy = 6,6′-dimethyl-2,2′-bipyridine-4,4′-dicarboxylic acid) (5), that has been used as standard, under the same experimental conditions. From a combination of electrochemical and absorption spectroscopy experiments, the MLCT energy levels of 2 are appropriate for electron injection onto the titania conduction band. Upon optimisation of the semiconductor's architecture, 2 proved to be the most efficient dye, reaching a conversion efficiency of η = 1.20%, which is slightly higher than that of 5 (η = 1.05%), mainly attributed to higher Voc values.

Graphical abstract: Sterically demanding pyridine-quinoline anchoring ligands as building blocks for copper(i)-based dye-sensitized solar cell (DSSC) complexes

Supplementary files

Article information

Article type
Paper
Submitted
21 jul 2022
Accepted
27 aug 2022
First published
29 aug 2022
This article is Open Access
Creative Commons BY license

Dalton Trans., 2022,51, 15049-15066

Sterically demanding pyridine-quinoline anchoring ligands as building blocks for copper(I)-based dye-sensitized solar cell (DSSC) complexes

A. Peppas, D. Sokalis, D. Perganti, G. Schnakenburg, P. Falaras and A. I. Philippopoulos, Dalton Trans., 2022, 51, 15049 DOI: 10.1039/D2DT02382B

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