Bichromophoric Photosensitizers: How and Where to Attach Pyrene Moieties to Phenanthroline to Generate Copper(I) Complexes

Merging of a pyrene moiety with a copper-(I)based photosensitizerenabled the development of superior bichromophoric systems. It hasbeen demonstrated that the exact position and type of substitutionis of crucial importance for the resulting properties and the photocatalyticactivity. Pyrene is a polycyclicaromatic hydrocarbon and organicdye thatcan form superior bichromophoric systems when combined with a transitionmetal-based chromophore. However, little is known about the effectof the type of attachment (i.e., 1- vs 2-pyrenyl) and the individual position of the pyrenyl substituentsat the ligand. Therefore, a systematic series of three novel diimineligands and their respective heteroleptic diimine-diphosphine copper-(I)complexes has been designed and extensively studied. Special attentionwas given to two different substitution strategies: (i) attachingpyrene via its 1-position, which occurs most frequentlyin the literature, or via its 2-position and (ii)targeting two contrasting substitution patterns at the 1,10-phenanthrolineligand, i.e., the 5,6- and the 4,7-position. In theapplied spectroscopic, electrochemical, and theoretical methods (UV/vis,emission, time-resolved luminescence and transient absorption, cyclicvoltammetry, density functional theory), it has been shown that theprecise choice of the derivatization sites is crucial. Substitutingthe pyridine rings of phenanthroline in the 4,7-position with the1-pyrenyl moiety has the strongest impact on the bichromophore. Thisapproach results in the most anodically shifted reduction potentialand a drastic increase in the excited state lifetime by more thantwo orders of magnitude. In addition, it enables the highest singletoxygen quantum yield of 96% and the most beneficial activity in thephotocatalytic oxidation of 1,5-dihydroxy-naphthalene.

Automated summary

The merging of a pyrene moiety with a copper-(I) based photosensitizer has resulted in the development of superior bichromophoric systems. The precise position and type of substitution play a crucial role in determining the properties and photocatalytic activity. Through extensive studies, it has been shown that attaching pyrene via its 1-position and substituting the pyridine rings of phenanthroline in the 4,7-position with the 1-pyrenyl moiety have the strongest impact on the bichromophore, resulting in significant improvements in reduction potential, excited state lifetime, single oxygen quantum yield, and photocatalytic activity.