Strongly blue fluorescent 1-phenyl-2-(pyridin-2-yl)-1H-phenanthro[9,10-d]imidazole (L1) is a facile block for the construction of multichromophore organic molecules, and simultaneously serves as a chelating diimine ligand. The coordination of L1 to zinc halides enhances the intraligand charge transfer and decreases the emission energy. For the iodide derivative, intra- and intermolecular heavy atom effects lead to a dual singlet–triplet emission with a temperature-dependent ratio of fluorescence and phosphorescence bands in the crystalline state. Decoration of the anthracene core with pyridyl-phenanthroimidazole units (L2 and L3) changes the localization of the lowest energy electronic transitions to the former polyaromatic motif. The solid-state photophysical characteristics of L2 and L3-based compounds strongly depend on the intermolecular interactions between the constituting π-systems (phenanthrene and anthracene), which are perturbed by the ZnX₂ coordinated fragments. Modulation of π-stacking contacts in these molecular materials containing L2 and L3 chromophores forms a basis for dynamic optical properties, responsive to mechanical, thermal, or chemical stimuli.

A series of diphosphine Re(I) complexes Re1–Re4 have been designed via decoration of the archetypal core {Re(CO)₂(N^N)} through the installations of the phosphines P⁰ and P¹ bearing the terminal double bond, where N^N = 2,2′-bipyridine (N^N1), 4,4′-di-tert-butyl-2,2′-bipyridine (N^N2) or 2,9-dimethyl-1,10-phenanthroline (N^N3) and P⁰ = diphenylvinylphosphine, and P¹ = 4-(diphenylphosphino)styrene. These complexes were copolymerized with the corresponding N-vinylpyrrolidone-based Macro-RAFT agents of different polymer chain lengths to give water-soluble copolymers of low-molecular p(VP-l-Re) and high-molecular p(VP-h-Re) block-copolymers containing rhenium complexes. Compounds Re1–Re4, as well as the copolymers p(VP-l-Re) and p(VP-h-Re), demonstrate phosphorescence from a ³MLCT excited state typical for this type of chromophores. The copolymers p(VP-l-Re#) and p(VP-h-Re#) display weak sensitivity to molecular oxygen in aqueous and buffered media, which becomes almost negligible in the model physiological media. In cell experiments with CHO-K1 cell line, p(VP-l-Re2) and p(VP-h-Re2) displayed significantly reduced toxicity compared to the initial Re2 complex and internalized into cells presumably by endocytic pathways, being eventually accumulated in endosomes. The sensitivity of the copolymers to oxygen examined in CHO-K1 cells via phosphorescence lifetime imaging microscopy (PLIM) proved to be inessential.

A series of bis-metalated phosphorescent [(N^C)₂Ir(bipyridine)]⁺ complexes with systematic variations in the structure and electronic characteristics of the N^C ligands were synthesized and characterized by using elemental analysis, mass spectrometry, NMR spectroscopy and X-ray crystallography. Investigation of the complexes’ spectroscopic properties together with DFT and TD DFT calculations revealed that metal-to-ligand charge transfer (MLCT) and intraligand (LC) transition play key roles in the generation of emissive triplet states. According to the results of theoretical studies, the ³LC excited state is more accurate to consider as an intraligand charge transfer process (ILCT) between N- and C-coordinated moieties of the N^C chelate. This hypothesis is completely in line with the trends observed in the experimental absorption and emission spectra, which display systematic bathochromic shifts upon insertion of electron-withdrawing substituents into the N-coordinated fragment. An analogous shift is induced by expansion of the aromatic system of the C-coordinated fragment and insertion of polarizable sulfur atoms into the aromatic rings. These experimental and theoretical findings extend the knowledge of the nature of photophysical processes in complexes of this type and provide useful instruments for fine-tuning of their emissive characteristics.

Two series of Au(III) pincer complexes [(C^N^C)AuL]ⁿ⁺ (C^N^C = 2,6-diphenylpyridine, L = alkynyl, n = 0; L = isocyanide, n = 1) have been synthesized and characterized in solution by NMR spectroscopy and mass spectrometry. The solid-state structures of alkynyl complexes were also analyzed with XRD crystallography. In a dilute CH₂Cl₂ solution, both alkynyl and isocyanide complexes display a similar weak blue phosphorescence originating from a metal-perturbed ³ILCT state localized on the pincer ligand, but their solid-state emission characteristics differ significantly. The isocyanide complexes exhibit strong bathochromic shifts of emission band maxima compared to those observed in solution, which can be assigned to the formation of aggregates that afford excimers with short Au-Au contacts in the T₁ emissive state. Among the neutral alkynyl analogues, two compounds retain essentially solution-like emissions, since their rigid crystalline environment precludes the excited-state transformation required for metal–metal bonding. Only the electron-rich dimethylamino derivative, which crystallizes as loosely packed dimers, exhibits a red-shifted solid-state band, and even this shift is substantially smaller than that of its isocyanide congener. The electronic structure of the complexes has been analyzed using DFT calculations, which corroborate the proposed rationalization of the observed trends in the emission characteristics and the difference in the aggregation behavior between the alkynyl and isocyanide chromophores.