Cyclometalated complexes [M­(Phbpy)­(CN)] (HPhbpy = 6-phenyl-2,2′-bipyridine) of the group 10 metals (Ni, Pd, and Pt) bearing a carbanionic –C∧N∧N pincer ligand were synthesized and studied in a combined experimental and computational DFT approach. All three complexes were crystallographically characterized showing closely packed dimers with head-to-tail stacking and short metal-metal contacts in the solid state. The computational models for geometries, excited states, and electronic transitions addressed both monomeric (Ni-mono, Pd-mono, and Pt-mono) and dimeric (Ni-dim, Pd-dim, and Pt-dim) entities. Photophysical properties and excited state dynamics of all title complexes were investigated in solution and in the solid at 298 and 77 K. [Ni­(Phbpy)­(CN)] and [Pd­(Phbpy)­(CN)] are virtually nonemissive in solution at 298 K, whereas [Pt­(Phbpy)­(CN)] shows phosphorescence in CH2Cl2 (DCM) solution (λ em = 562 nm) stemming from a mixed 3MLCT/ILCT (metal-to-ligand charge transfer/​intraligand charge transfer) state. At 77 K in a glassy frozen DCM:​MeOH matrix, [Pd­(Phbpy)­(CN)] shows a remarkable emission (λ em = 571 nm) with a photoluminescence quantum yield reaching almost unity, whereas [Ni­(Phbpy)­(CN)] is again nonemissive. Calculations on the monomeric models M-mono show that low-lying metal-centered states (MC, i.e., d-d* configuration) with dissociative character quench the photoluminescence. In the solid state, the complexes [M­(Phbpy)­(CN)] show defined photoluminescence bands (λ em = 561 nm for Pd and 701 nm for Pt). Calculations on the dimeric models M-dim shows that the axial M···M interactions alter the photophysical properties of Pd-dim and Pt-dim toward MMLCT (metal-metal-to-ligand charge transfer) excited states with Pd-dim showing temperature-dependent emission lifetimes, suggesting thermally activated delayed fluorescence, whereas Pt-dim displayed phosphorescence with excimeric character. The metal-metal interactions were analyzed in detail with the quantum theory of atoms in molecules approach.

The series of chelating phosphine ligands, which contain bidentate P 2 (bis[(2-diphenylphosphino)phenyl] ether, DPEphos; 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Xantphos; 1,2-bis(diphenylphosphino)benzene, dppb), tridentate P 3 (bis(2-diphenylphosphinophenyl)phenylphosphine), and tetradentate P 4 (tris(2-diphenylphosphino)phenylphosphine) ligands, was used for the preparation of the corresponding dinuclear [M(μ 2 -SCN) P 2 ] 2 (M = Cu, 1 , 3 , 5 ; M = Ag, 2 , 4 , 6 ) and mononuclear [CuNCS( P 3 /P 4 )] ( 7 , 9 ) and [AgSCN( P 3 /P 4 )] ( 8 , 10 ) complexes. The reactions of P 4 with silver salts in a 1:2 molar ratio produce tetranuclear clusters [Ag 2 (μ 3 -SCN)(t-SCN)( P 4 )] 2 ( 11 ) and [Ag 2 (μ 3 -SCN)( P 4 )] 2 2+ ( 12 ). Complexes 7 – 11 bearing terminally coordinated SCN ligands were efficiently converted into derivatives 13 – 17 with the weakly coordinating – SCN:B(C 6 F 5 ) 3 isothiocyanatoborate ligand. Compounds 1 and 5 – 17 exhibit thermally activated delayed fluorescence (TADF) behavior in the solid state. The excited states of thiocyanate species are dominated by the ligand to ligand SCN → π(phosphine) charge transfer transitions mixed with a variable contribution of MLCT. The boronation of SCN groups changes the nature of both the S 1 and T 1 states to (L + M)LCT d,p(M, P) → π(phosphine). The localization of the excited states on the aromatic systems of the phosphine ligands determines a wide range of luminescence energies achieved for the title complexes (λ em varies from 448 nm for 1 to 630 nm for 10c ). The emission of compounds 10 and 15 , based on the P 4 ligand, strongly depends on the solid-state packing (λ em = 505 and 625 nm for...

A series of diimine ligands has been designed on the basis of 2-pyridyl-1H-phenanthro[9,10-d]imidazole (L1, L2). Coupling the basic motif of L1 with anthracene-containing fragments affords the bichromophore compounds L3–L5, of which L4 and L5 adopt a donor–acceptor architecture. The latter allows intramolecular charge transfer with intense absorption bands in the visible spectrum (lowest λabs 464 nm (ε = 1.2 × 104 M–1 cm–1) and 490 nm (ε = 5.2 × 104 M–1 cm–1) in CH2Cl2 for L4 and L5, respectively). L1–L5 show strong fluorescence in a fluid medium (Φem = 22–92%, λem 370–602 nm in CH2Cl2); discernible emission solvatochromism is observed for L4 and L5. In addition, the presence of pyridyl (L1–L5) and dimethylaminophenyl (L5) groups enables reversible alteration of their optical properties by means of protonation. Ligands L1–L5 were used to synthesize the corresponding [Re(CO)3X(diimine)] (X = Cl, 1–5; X = CN, 1-CN) complexes. 1 and 2 exhibit unusual dual emission of singlet and triplet parentage, which originate from independently populated 1ππ* and 3MLCT excited states. In contrast to the majority of the reported Re(I) carbonyl luminophores, complexes 3–5 display moderately intense ligand-based fluorescence from an anthracene-containing secondary chromophore and complete quenching of emission from the 3MLCT state presumably due to the triplet–triplet energy transfer (3MLCT → 3ILCT).

Luminescent cyclometalated complexes [M(C^N^N)CN] (M=Pt, Pd; HC^N^N=pyridinyl‐ (M=Pt 1, Pd 5), benzyltriazolyl‐ (M=Pt 2), indazolyl‐ (M=Pt 3, Pd 6), pyrazolyl‐phenylpyridine (M=Pt 4)) decorated with cyanide ligand, have been explored as nucleophilic building blocks for the construction of halogen‐bonded (XB) adducts using IC6F5 as an XB donor. The negative electrostatic potential of the CN group afforded CN⋅⋅⋅I noncovalent interactions for platinum complexes 1–3; the energies of XB contacts are comparable to those of metallophilic bonding according to QTAIM analysis. Embedding the chromophore units into XB adducts 1–3⋅⋅⋅IC6F5 has little effect on the charge distribution, but strongly affects Pt⋅⋅⋅Pt bonding and π‐stacking, which lead to excited states of MMLCT (metal–metal‐to‐ligand charge transfer) origin. The energies of these states and the photoemissive properties of the crystalline materials are primarily determined by the degree of aggregation of the luminophores via metal–metal interactions. The adduct formation depends on the nature of the metal and the structure of the metalated ligand, the variation of which can yield dynamic XB‐supported systems, exemplified by thermally regulated transition 3↔3⋅⋅⋅IC6F5.

The series of cyanide-bridged coordination polymers [(P )CuCN] (1), [(P )Cu{M(CN) }] (M=Cu 3, Ag 4, Au 5) and molecular tetrametallic clusters [{(P )MM'(CN)} ] (MM'=Cu 6, Ag 7, AgCu 8, AuCu 9, AuAg 10) were obtained using the bidentate P and tetradentate P phosphane ligands (P =1,2-bis(diphenylphosphino)benzene; P =tris(2-diphenylphosphinophenyl)phosphane). All title complexes were crystallographically characterized to reveal a zig-zag chain arrangement for 1 and 3-5, whereas 6-10 possess metallocyclic frameworks with different degree of metal-metal bonding. The d -d interactions were evaluated by the quantum theory of atoms in molecules (QTAIM) computational approach. The photophysical properties of 1-10 were investigated in the solid state and supported by theoretical analysis. The emission of compounds 1 and 3-5, dominated by metal-to-ligand charge transfer (MLCT) transitions located within {CuP } motifs, is compatible with thermally activated delayed fluorescence (TADF) behaviour and a small energy gap between the T and S excited states. The luminescence characteristics of 6-10 are strongly dependent on the composition of the metal core; the emission band maxima vary in the range 484-650 nm with quantum efficiency reaching 0.56 (6). The origin of the emission for 6-8 and 10 at room temperature is assigned to delayed fluorescence. AuCu cluster 9, however, exhibits only phosphorescence that corresponds to theoretically predicted large value ΔE(S -T ). DFT simulation highlights a crucial impact of metallophilic bonding on the nature and energy of the observed emission, the effect being greatly enhanced in the excited state.