Tuning the photoelectric response of pyrene-based coordination polymers by optimizing charge transfer

Abstract

In this work, we report three π–π stacked coordination polymers (CPs) [CoL₂(bipy)_0.5]_n (1), [CdL₂(bipy)_0.5]_n (2) and [CdL(bpt)_0.5(NO₃)]_n (3) for application of photoelectric response (HL = E-2-(3-(pyren-1-yl)acryloyl)benzoic acid, bipy = 4,4-bipyridine, bpt = 2,5-dipyridin-4-yl-1,3,4-thiadiazole). And the effect of charge transfer on the photoelectric properties is explored by adjusting the composition and π-stacking fashion of the CPs. Spectroscopic experiments and theoretical calculations were also used to gain further insight into the electronic structure characteristics of the three CPs. The long-lasting phosphorescence lifetime of 2 and 3 could facilitate efficient exciton hopping and large exciton displacement in CPs. The smaller HOMO–LUMO energy gaps suggest strong semiconductor-like properties of 1–3. Optoelectronic measurements indicate that 3 exhibits the highest photocurrent density up to 4.02 μA cm⁻², 2 and 11 times higher than that of 2 (1.97 μA cm⁻²) and 1 (0.36 μA cm⁻²). The experimental results show that employing transition metals with d¹⁰ nature and constructing strong π–π stacking for efficient charge transport are significant to achieve high photoelectric conversion. Our work has fundamental guiding significance for the design of new complexes for photoelectric conversion.