Development of earth-abundant copper photosensitizers for artificial photosynthesis

Abstract

A series of bis(arylimino)acenaphthene (Ar-BIAN) CuI complexes have been synthesized in three or fewer steps. A comprehensive study of their electrochemical and spectroscopic properties has been performed. The Ar-BIAN CuI complexes herein have been incorporated into dye-sensitized solar cells (DSSCs) or photoredox reaction to investigate their potential applications. In Chapter 2, two new Ar-BIAN ligands and their corresponding homoleptic CuI complexes were synthesized and studied. The solution and solid-state absorption characteristics of the complexes have been examined. They were found to be panchromatic and absorb into the near-infrared (NIR) region. Notably, the crystal structure of one of the complexes gave an unprecedented rhombically distorted square planar geometry about the metal center. Computational studies revealed the non-covalent interactions between the aromatic functionalities and among the iodide atoms. To investigate the practical application of the complexes, they were anchored onto a metal oxide surface and incorporated into dye-sensitized solar cells (DSSCs). However, the efficiencies obtained and discussed in Chapter 3 were lower than expectations. In Chapter 4, another group of panchromatic Ar-BIAN CuI complexes were synthesized and characterized. Electrochemical measurements showed that two of the complexes can be regenerated after redox activities. From the photoluminescence experiments, one of the complexes displayed a weakly emissive signal. According to the time-correlated single-photon counting (TCSPC) measurements, the photoluminescence has a bi-exponential lifetime (τ1 = 3.6 ns; τ2 = 11 ns). Following on, the luminescent complex was employed in the photocatalysis of atom transfer radical addition (ATRA) reactions. Spectroelectrochemical studies were carried out to obtain the UV-visible absorption spectra of the CuII species formed upon oxidation. A comparison of the absorption spectra of the independently synthesized CuII complex and the species formed during the photoredox reaction led us to conclude that the intermediate contained CBr3 or Br- attached to the CuII metal center.