Chromophore-Functionalized Phenanthro-diimine Ligands and Their Re(I) Complexes

Abstract

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).

Diversifying the luminescence of phenanthro-diimine ligands in zinc complexes

“…Ligands L1 and L2, containing a pyridyl-imidazole coordinating function fused with a polyaromatic phenanthrene motif, were readily obtained as described earlier. 45,46 L3, which comprises diethynylanthracene decorated with two diimine motifs, was synthesized in a good yield analogously to L2 (Scheme S1, see the experimental details in the ESI †).…”

“…1), which are known to be fluorescent in solution. 45 Binding these chromophores to some ZnX 2 salts (X = Cl, I, OAc) has a substantial impact on the solid state photophysical behavior. A range of intermolecular contacts were found to be subtly dependent on the anions X and allowed realizing such phenomena as temperature-variable dual emission and mechanochromic luminescence, which could not be attained for the parent organic compounds.…”

Experimental and computational exploration of photophysical and electroluminescent properties of modified 2,2′:6′,2″‐terpyridine, 2,6‐di(thiazol‐2‐yl)pyridine and 2,6‐di(pyrazin‐2‐yl)pyridine ligands and their Re(I) complexes

“…Dual charge transfer has been also confirmed in Re(I) thioether substituted hexaazanaphthalene complexes . It is assumed that photoexcitation of these systems can optically populate both ligand‐centred 1 ππ* and 1 MLCT states, which can potentially relax via independent pathways . Coexistence of the distinct excited states offers additional opportunity for fine‐tuning the luminescent properties of this class of compounds.…”

Electron‐donor substituents on the dppz‐based ligands to control luminescence from dark to bright emissive state in Ir(III) complexes

“…The versatility that offer the different substitution positions of the dipyrido[3,2‐a:2′,3′‐c]phenazine (dppz) ligand as well as prolongation of their π‐systems has allowed the synthesis of many dppz derivates and also of their respective coordination complexes with Ru(II), Cu(II), Re(I), Rh(III), Ir(III), Os(II), and Pd(II) . Nevertheless, main research involving dppz‐based complexes have focused in applications related to photosensitizers and intercalation into DNA to probe their cytotoxic properties .…”

“…This strategy offer numerous alternatives to modulate the electronic properties of the ligand and their complexes, due to the abundant types of diamine that can be employed . Regarding to the dppz structure, this ligand is considered to be constituted by two fragments: bipyridine ( bpy ) and phenazine ( phz ) . Related to the photophysical properties of the coordination compounds with this type of ligands, two triplet excited states are identified: triplet metal to ligand‐ bpy charge transfer ( 3 MLCT bpy ) and triplet metal to ligand‐ phz charge transfer ( 3 MLCT phz ) .…”