Spectroscopic and Crystallographic Investigations of Novel BODIPY-Derived Metal-Organic Frameworks

To explore new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-derived metalorganic frameworks (MOFs), we employed 2,6-dicarboxyl-1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene (H2L) as a ligand to successfully synthesize five coordination polymers, namely, {[Zn-2(L)(2)(bpp)].2H(2)O.2EtOH}(n) (<bold>1</bold>), {[Cd-2(L)(2)(bpp)].2H(2)O.EtOH}(n) (<bold>2</bold>), {[Cd-2(L)(bpe)(3)(NO3)(2)].2H(2)O.DMF.EtOH}(n) (<bold>3</bold>), {[Cd(L)(bpe)(0).(5)(DMF)(H2O)]}(n) (<bold>4</bold>), and {[Cd(L)(bpe)(0).(5)].1.5H(2)O.DMF}(n) (<bold>5</bold>) (bpp = 1,3-bi(4-pyridyl)propane, bpe = 1,2-bi(4-pyridyl)ethane). Except for two 2D-layer coordination polymers <bold>3</bold> and <bold>4</bold>, the rest samples exhibit 3D metalorganic frameworks with certain pore sizes, especially MOFs <bold>1</bold> and <bold>5</bold>. Spectroscopic and crystallographic investigations demonstrate that the absorption and emission energies of the BODIPY chromophores are sensitive to the coordination modes. Moreover, in case <bold>2</bold>, the transition metal centers coordinated with the dicarboxylate ligands L-2 are capable of forming the two BODIPY units in coplanar arrangements (theta = 37.9 degrees), simultaneously suppressing the uncommon J-dimer absorption band centered at 705 nm with a long tail into the near-infrared region at room temperature. On the other hand, in comparison with the ligand H2L, the emission of monomer-like BODIPY in case <bold>3</bold> is enhanced in the solid state by a considerably long distance between the parallel BODIPY planes (about 14.0 angstrom).