Naphthalene-1,8-dicarboxylate based zinc coordination polymers: a photophysical study

Abstract

Herein, we report the synthesis and photoluminescence properties of a new 1,3-dioxo-2-(1H-tetrazol-5-yl)-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic (H₃L) ligand and three coordination polymers (CPs). Compound [Zn(ntca)DMF]_n·DMF (1) (ntca²⁻ = 1,4,5,8-naphthalenetetracarboxylate 1,8-monoanhydride, DMF = N,N-dimethylformamide) formed 1D coordination polymer chains packed by hydrogen bonding interactions. On its part, compounds namely [(CH₃)₂NH₂](Zn₂(μ-OH)(L)(5-NH₂-tetrazolate)_n·2H₂O (2) and [(CH₃)₂NH₂](ZnL)_n (3) (where H₃L stands for 1,3-dioxo-2-(1H-tetrazol-5-yl)-2,3-dihydro-1H-benzo[de]isoquinoline-6,7-dicarboxylic acid) crystallize as 2D-layered and 3D anionic frameworks containing dimethylammonium cations occupying the voids. Photoluminescence (PL) measurements have been performed in the solid state on all CPs and ligands to characterize their emission properties, including variable-temperature spectra, lifetime and efficiency. Moreover, the photophysical properties have been studied from the theoretical viewpoint by means of time dependent density functional theory (TD-DFT) in order to elucidate the mechanisms and electronic transitions governing the process. Compounds 1 and 3 present an intense blue luminescence which was originated in the electronic transitions of the ntca²⁻ and the L³⁻ ligands. Compound 2 displays a lower quantum yield which could be tentatively attributed to the weak π–π interactions of the aromatic clouds of L³⁻ or the molecular vibrations and/or possible rotational motions of the 5-amino-tetrazolate co-ligand.