In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2′:6′,2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet 3 IL aryl that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective. The attachment of the electron-rich pyrenyl group resulted in a noticeable red shift and a significant increase in molar absorption coefficients of the lowest energy absorption of the resulting Re(I) complexes due to the contribution of intraligand charge-transfer (ILCT) transitions occurring from the pyrenyl substituent to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO) 3 (L n -κ 2 N )] with 1-pyrenyl-functionalized ligands were found to have predominant 3 IL pyrene / 3 ILCT pyrene→terpy character. The 3 IL/ 3 ILCT nature of the lowest energy excited state of [ReCl(CO) 3 (4′-(1-pyrenyl)-terpy-κ 2 N )] was also evidenced by nanosecond transient absorption and time-resolved emission spectroscopy. Enhanced room-temperature emission lifetimes of the complexes [ReCl(CO) 3 (L n -κ 2 N )] with 1-pyrenyl-substituted ligands are indicative of the thermal activation between 3 MLCT and 3 IL/ 3 ILCT excited states. Deactivation pathways occurring upon light excitation in [ReCl(CO) 3 (4′-(1-naphthyl)-terpy-κ 2 N )] and [ReCl(CO) 3 (4′-(1-pyrenyl)-terpy-κ 2 N )] were determined by femtosecond transient absorption studies.

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The impact of highly electron donating units appended to the imine ligand on the thermal and optoelectronic properties of Re(i) complexes was investigated.

H NMR (400 MHz, DMSO-d 6 , δ, ppm): 10.34 (s, 1H), 9.17 (d, J = 1.8 Hz, 1H), 9.11 (d, J = 1.2 Hz, 2H), 8.96 (d, J = 3.0 Hz, 1H), 8.90 (t, J = 2.2 Hz, 2H), 8.25 (d, J = 1.8 Hz, 1H), 8.18 (d, J = 9.0 Hz, 2H), 6.72 (d, J = 9.0 Hz, 2H), 3.38 (d, J = 6.5 Hz, 4H), 2.01 (t, J = 6.4 Hz, 4H).13C NMR not recorded due to insufficient complex solubility. HRMS (ESI): calcd for C 26 H 20 N 6 O 3 ReCl [M + Na] + 709.13 g mol −1 ; found 709.07 g mol −1 .

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In this work, the structure–property relationship was investigated for a series of Re­(I) carbonyls [ReCl­(CO)3(R-terpy-κ2N)], [ReCl­(CO)3(R-dtpy-κ2N)], and [ReCl­(CO)3(R-dppy-κ2N)]. The studied compounds bear 2,2′:6′,2″-terpyridines (R-terpy), 2,6-di­(thiazol-2-yl)­pyridines (R-dtpy), and 2,6-di­(pyrazin-2-yl)­pyridines (R-dppy) functionalized with strongly electron-donating cyclic (piperidine and morpholine) and acyclic (dimethylamine, diphenylamine) amine donor attached to the central pyridine ring of the triimine skeleton via phenylene linkage. Their thermal properties were evaluated using DSC. The ground- and excited-state properties of these systems were elucidated with electrochemistry, absorption and emission spectroscopy, and density-functional theory (DFT)-based calculations. The terpy skeleton was found to efficiently stabilize the LUMO orbital, as manifested by the most negative reduction potentials for Re­(I) terpyridine complexes and significant blue-shift of the absorption and emission of [ReCl­(CO)3(R-terpy-κ2N)] in relation to those of Re­(I) carbonyls bearing dtpy- and dppy-based ligands. Substitution of the triimines with amine substituents resulted in participation of intraligand charge-transfer (ILCT) transitions, and it was found to be beneficial for hole-transport properties of the Re­(I) carbonyls. The constructed nondoped and doped single layer diodes based on Re­(I) complexes emitted red light with various intensity.

Two gold(iii) complexes incorporating 2,2':6',2''-terpyridine derivatives have been synthesised and characterized, and the possibility of tuning the cytotoxic activity by structural modifications of a terpy ligand has been examined. Both complexes [AuCl(4'-R-terpy)](PF) (1) and [AuCl(4'-R-terpy)](PF) (2), where R is 2-pyridyl and R is 3-pyridyl, show good anti-proliferative activities against HCT116, which are higher in relation to those of the free ligands, [AuCl(terpy)](PF) and standard anticancer drug cisplatin. The cytotoxic properties of the gold complexes were examined by MTS assay, cell cycle and apoptosis analysis, ROS measurements, determination of mitochondrial membrane potential and mass, and staining of phosphatidylserine with Annexin-V antibody FITC-conjugated together with PI.

Structural, spectroscopic and electrochemical properties of six complexes [AuCl(L1)](PF6)2·CH3CN (1), [AuCl(L2)](PF6)2 (2), [PtCl(L1)](BPh4)·CH3CN (3), [PtCl(L2)](SO3CF3) (4), [CuCl2(L1)] (5) and [CuCl2(L2)]·CH3CN (6) with modified 2,2':6',2''-terpyridine ligands, 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (L1) and 4'-(4-methoxynaphthalen-1-yl)-2,2':6',2''-terpyridine (L2) were thoroughly investigated and a significant role of the substituent (4-methoxyphenyl or 4-methoxynaphthalen-1-yl) and the metal center was demonstrated. The naphthyl-based substituent was found to increase the emission quantum yield of the luminescent Au(iii) and Pt(ii) complexes. Furthermore, the antiproliferative potential of the reported complexes was examined towards human colorectal (HCT116) and ovarian (A2780) carcinoma cell lines as well as towards normal human fibroblasts. The Au(iii) complex 2 and Cu(ii) complex 5 were found to have a higher antiproliferative effect on HCT116 colorectal and A2780 ovarian carcinoma cells when compared with the Pt(ii) complex with the same ligand (4). The order of cytotoxicity in both cell lines is 2 > 6 > 1 > 3 > 4. Complex 2 seems to be more cytotoxic towards HCT116 and A2780 cancer cell lines with IC50 values 300× and 130× higher in normal human fibroblasts compared to the respective cancer cells. The viability loss induced by the complexes agrees with Hoechst 33258 staining and the typical morphological apoptotic characteristics like chromatin condensation and nuclear fragmentation and flow cytometry assay. The induction of apoptosis correlates with the induction of reactive oxygen species (ROS). Fluorescence microscopy analysis indicates that after 3 h of incubation, complexes 1-4 are localized inside HCT116 cells and the high levels of internalization correlate with their cytotoxicity.