Band Gaps and Photocurrent Responses of Bulk and Thin-film Coordination Polymers Based on 3,6-di(1H-imidazol-1-yl)-9H-carbazole

Based on a novel rigid N-donor, 3,6-di(1H-imidazol-1-yl)-9H-carbazole (L), two CPs formulated as CdL(L1)3DMF (H2L1 = 4,4'-carbonyldibenzoic acid, DMF = N,N'-dimethylformamide) (1) and Cu2L2(SO4) (2) have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. CP 1 exhibits a two-dimensional (2D) structure, and CP 2 shows a one-dimensional (1D) chain. The two CPs exhibit different quasi-reversible redox properties and they possess very weak photoluminescence properties. Density functional theory (DFT) calculation and experiment results show that CP 1 has wider band gap than CP 2. Notably, CP 2 produces higher photocurrent density than CP 1 upon the visible light illumination, which is also in agreement with their Nyquist plots and MottSchottky curves. The thin-film CP 1 has been obtained via physical exfoliation in methanol, and it shows more active electrochemical behavior and enhanced photoresponse than bulk CP 1.

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