An Alkynyl-Dangling Ru(II) Polypyridine Complex for Targeted Antimicrobial Photodynamic Therapy

To realize clinical application of antibacterial photodynamic therapy (aPDT), one of the most arduous challenges is how to render aPDT agents high selectivity against bacterial pathogens. In light of the fact that amino group-containing lipids are rich on the outer surfaces of Gram-positive bacteria, we herein constructed an alkynyl-dangling ruthenium(II) polypyridine complex (Ru2) to preferentially label Staphylococcus aureus (S. aureus) and methicillin-resistant Staphylococcus aureus (MRSA) over mammalian cells via the amino-yne bio-orthogonal click reaction. Thanks to the strong singlet oxygen generation ability, Ru2 could photo-inactivate S. aureus and MRSA effectively and specifically. Phosphatidylethanolamine (PE) molecules also exist in mammalian cells but are not accessible for Ru2, leading to its poor binding/uptake and negligible cytotoxicity in the dark and upon irradiation towards mammalian cells as well as low hemolysis, all favorable for aPDT application.     

Synthesis,Characterization, and Antimicrobial Evaluation of Sulfonamides Containing N-Acyl Moieties Catalyzed by Bismuth(III) Salts Under Both Solvent and Solvent-Free Conditions

Efficient N-acylation of sulfonamides with both readily available carboxylic acid chlorides and anhydrides has been carried out with catalysis by bismuth(III) salts including BiCl₃ and Bi (OTf)₃. The reactions proceed rapidly in both heterogeneous and solvent-free conditions and afforded the corresponding N-acylsulfonamides in good to excellent yields. The mild reaction conditions and low toxicity of bismuth salts make this procedure attractive and in close agreement with the goals of green chemistry. Some of the synthesized compounds were evaluated in vitro as antimicrobial agents against representative strains of Gram-positive (Staphylococcus aureus ATCC 25922, clinical strains of Staphylococcus aureus VISA and Enterococcus spp.) and Gram-negative bacteria (Pseudomonas aeruginosa ATCC 27853, clinical strains of Klebsiella pneumonia and Escherichia coli) and as antifungal agents against Candida albicans (clinically isolated) by both disc diffusion and minimal inhibition concentration (MIC) methods. All these bacteria and fungi studied were screened against some antibiotics to compare with our chemicals' zone diameters.     

Synthesis,characterization and antimicrobial activity of 3,5-di-tert-butylsalicylaldehyde-S-methylthiosemicarbazones and their Ni(II) complexes

Ni(II) complexes were prepared by the reactions of 3,5-di-tert-butylsalicylaldehyde-S-methylisothiosemicarbazone (L) with salicylaldehyde or 2-hydroxy-1-naphthaldehyde in the presence of NiCl₂·6H₂O. The complexes and starting material L were characterized by physic-chemical analysis and spectroscopic techniques such as ¹HNMR, ¹³CNMR, IR and UV–VIS. Antimicrobial activity studies of L and the two complexes standards strains of bacteria (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Bacillus cereus, Enterococcus faecalis, Streptococcus pneumoniae, Listeria monocytogenes, Escherichia coli, Salmonella typhi and Candida albicans) and 22 clinically isolated microorganisms, including multidrug resistant pathogenic microorganisms, were carried out. The free thiosemicarbazone L showed a significant inhibition of the growth all of Gram-positive bacteria tested.     

A new pyrimidine-derived ligand,N-pyrimidine oxalamic acid,and its Cu(II), Co(II), Mn(II), Ni(II), Zn(II), Cd(II), and Pd(II) complexes: synthesis,characterization, electrochemical properties,and biological activity

A new heterocyclic compound N-(5-benzoyl-2-oxo-4-phenyl-2H-pyrimidin-1-yl)-oxalamic acid has been synthesized from N-amino pyrimidine-2-one and oxalylchloride. Bis-chelate complexes of the ligand were prepared from acetate/chloride salts of Cu(II), Co(II), Mn(II), Ni(II), Zn(II), Cd(II), and Pd(II) in methanol. The structures of the ligand and its metal complexes were characterized by microanalyses, IR, AAS, NMR, API-ES, UV-Vis spectroscopy, magnetic susceptibility, and thermogravimetric analyses. An octahedral geometry has been suggested for all the complexes, except for Pd(II) complex, in which the metal center is square planar. Each ligand binds using C(2)=O, HN, and carboxylate. The cyclic voltammograms of the ligand and the complexes are also discussed. The new synthesized compounds were evaluated for antimicrobial activities against Gram-positive, Gram-negative bacteria and fungi using the microdilution procedure. The Cu(II) complex displayed selective and effective antibacterial activity against one Gram-positive spore-forming bacterium (Bacillus cereus ATCC 7064), two Gram-positive bacteria (Staphylococcus aureus ATCC 6538 and S. aureus ATCC 25923) at 40–80 µg mL^?1, but poor activity against Candida species. The Cu(II) complex might be a new antibacterial agent against Gram-positive bacteria.     

氟化修饰显著提高碳点的抗菌活性

本文采用支化聚乙烯亚胺和乙醇制备阳离子碳点,并在其表面接枝含氟烷基链,得到一种氟化修饰的碳点材料,其对革兰氏阳性菌金黄色葡萄球菌以及革兰氏阴性菌大肠杆菌和绿脓杆菌都表现出了优异的抗菌活性,而对哺乳动物细胞具有较低的毒性。通过构效关系研究发现,氟化修饰对于碳点的抗菌活性至关重要,将含氟烷基链替换成烷烃基链会极大削弱碳点的抗菌性能。本文的结果为阳离子抗菌材料的设计提供了新的思路。     

Membrane-Anchoring Photosensitizer with Aggregation-Induced Emission Characteristics for Combating Multidrug-Resistant Bacteria

Traditional photosensitizers (PSs) show reduced singlet oxygen (¹O₂) production and quenched fluorescence upon aggregation in aqueous media, which greatly affect their efficiency in photodynamic therapy (PDT). Meanwhile, non-targeting PSs generally yield low efficiency in antibacterial performance due to their short lifetimes and small effective working radii. Herein, a water-dispersible membrane anchor (TBD-anchor) PS with aggregation-induced emission is designed and synthesized to generate ¹O₂ on the bacterial membrane. TBD-anchor showed efficient antibacterial performance towards both Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Over 99.8 % killing efficiency was obtained for methicillin-resistant S. aureus (MRSA) when they were exposed to 0.8 μm of TBD-anchor at a low white light dose (25 mW cm⁻²) for 10 minutes. TBD-anchor thus shows great promise as an effective antimicrobial agent to combat the menace of multidrug-resistant bacteria.     

Synthesis,characterization, and antibacterial activity of yttrium(III) complexes with 2,6-pyridinedicarboxylate and pyridine

A series of metal coordination complexes of yttrium(III) containing 2,6-pyridinedicarboxylate and pyridine have been prepared with different molar ratios of yttrium(III) to 2,6-pyridinedicarboxylate in aqueous pyridine solutions, and characterized by elemental analysis, infrared spectra, nuclear magnetic resonance, and thermal analyses. The in vitro antibacterial activities of the complexes have also been investigated against microorganisms such as Gram-negative bacteria Bacillus coli and Gram-positive bacteria Staphylococcus aureus by the disc diffusion method in DMSO. When compared to previous results, the yttrium(III) complexes of 2,6-pyridinedicarboxylate and pyridine have a moderate effect on microorganisms due to the presence of the pyridine group.     

Synthesis,spectral studies,and antimicrobial activity of binary and ternary Cu(II), Ni(II), and Fe(III) complexes of new hexadentate Schiff bases derived from 4,6-diacetylresorcinol and amino acids

Two new hexadentate N₂O₄ donor Schiff bases, H₄L¹ and H₄L², were synthesized by condensation of 4,6-diacetylresorcinol with glycine and alanine, respectively. The structures of the ligands were elucidated by elemental analyses, IR, ¹H NMR, electronic, and mass spectra. Reactions of the Schiff bases with copper(II), nickel(II), and iron(III) nitrates in 1 : 2 molar ratio gave binuclear metal complexes and, in the presence of 8-hydroxyquinoline (8-HQ) or 1,10-phenanthroline (Phen) as secondary ligands (L′), mixed-ligand complexes in two molar ratios 1 : 2 : 2 and 1 : 2 : 1 (L¹/L² : M : L′). The complexes were characterized by elemental and thermal analyses, IR, electronic, mass, and ESR spectral studies, as well as conductivity and magnetic susceptibility measurements. The spectroscopic data reveal that the Schiff-base ligands were dibasic or tetrabasic hexadentate ligands. The coordination sites with the metal ions are two azomethine nitrogens, two oxygens of phenolic groups, and two oxygens of carboxylic groups. Copper(II) complexes were octahedral and square planar while nickel(II) and iron(III) complexes were octahedral. The Schiff bases, H₄L¹ and H₄L², and some of their metal complexes showed antibacterial activity towards Gram-positive (Staphylococcus aureus and Streptococcus pyogenes) and Gram-negative (Pseudomonas fluorescens and Pseudomonas phaseolicola) bacteria and antifungal activity towards the fungi Fusarium oxysporium and Aspergillus fumigatus.     

The Impact of Crystal Packing and Aurophilic Interactions on the Luminescence Properties in Polymorphs and Solvate of Aroylacetylide–Gold(I) Complexes

The influence of the chemical substitution, crystal packing, and aurophilic interactions of the gold(I) acetylide complexes of the type (ArCOC≡C)_nAuPEt₃ (n=1,2) on their luminescent properties were examined. All described complexes undergo ligand scrambling in solution, which results in the formation of stable, easily isolated crystals that contain [ArCO(C≡C)_n]₂Au⁻(Et₃P)₂Au⁺ homoleptic species. In particular, we observed that the (benzoylacetylide)gold(I) complex yields three crystal forms with strikingly different luminescence properties. We monitored the conversion pathway for these forms: an orange luminescent form of homoleptic complex upon drying undergoes spontaneous transformation to bright green fluorescent form and finally to the weakly blue emissive one. In addition, we report a rare example of a helical arrangement of Au⋅Au⋅Au chains that are observed for the first time in acetylide gold(I) complexes in the case of heteroleptic (benzoylacetylide)gold(I) complex. This is a very rare case in which crystal structures and ensuing electronic properties of the heteroleptic and Au^I complexes could be directly compared.     

Synthesis and Characterisation of Bismuth(III) Aminoarenesulfonate Complexes and Their Powerful Bactericidal Activity against Helicobacter pylori

The synthesis and characterisation of nine new tris‐substituted bismuth(III) aminoarenesulfonates of the general formula [Bi(O₃S‐R^N)₃] (R^N=o‐aminophenyl 1 , m‐aminophenyl 2 , 6‐amino‐3‐methoxyphenyl 3 , p‐aminophenyl 4 , 2‐pyridyl 5 , o‐aminonaphthyl 6 , 5‐aminonaphthyl 7 , 4‐amino‐3‐hydroxynaphthyl 8 and 5‐isoquinolinyl 9 ) is described. Two synthetic strategies, using Ag₂O and [Bi(OtBu)₃], were explored and compared. The possibility to access heteroleptic bismuth(III) complexes with the new silver(I) metathesis reaction is demonstrated with the synthesis of the heteroleptic bismuth(III) aminoarenesulfonate complexes [PhBi(O₃S‐P2)₂(dmso)] 10 , [Ph₂Bi(O₃S‐P2)]_∞ 11 and [PhBi(O₃S‐P2)₂]_∞ 12 , of which the solid state structures 10 and 12 are presented (2P‐SO₃^?=2‐pyridinesulfonate). These complexes offer remarkable in‐vitro activity against three standard laboratory strains of Helicobacter pylori (H. pylori) as demonstrated by their exceptionally low minimum inhibitory concentration (MIC) values of 0.049 μg mL^?1 for the strains 251 and B128, which places most MIC values in the nano‐molar region. These results demonstrate the importance of the amino functionality in addition to the sulfonate group on the bactericidal properties against H. pylori.     

Evaluation of Ruthenium(II) N-Heterocyclic Carbene Complexes as Antibacterial Agents and Inhibitors of Bacterial Thioredoxin Reductase

A series of ruthenium(II) complexes with N-heterocyclic carbene (NHC) ligands of the general type (arene)(NHC)Ru(II)X₂ (where X = halide) was prepared, characterized, and evaluated as antibacterial agents in comparison to the respective metal free benzimidazolium cations. The ruthenium(II) NHC complexes generally triggered stronger bacterial growth inhibition than the metal free benzimidazolium cations. The effects were much stronger against Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus) than against Gram-negative bacteria (Escherichia coli, Acinetobacter baumannii, Pseudomonas aeruginosa), and all complexes were inactive against the fungus Candida albicans. Moderate inhibition of bacterial thioredoxin reductase was confirmed for selected complexes, indicating that inhibition of this enzyme might be a contributing factor to the antibacterial effects.     

Homo‐ and Heteroleptic Bismuth(III/V) Thiolates from N‐Heterocyclic Thiones: Synthesis,Structure and Anti‐Microbial Activity

Homo‐ and heteroleptic bismuth thiolato complexes have been synthesised and characterised from biologically relevant tetrazole‐, imidazole‐, thiadiazole‐ and thiazole‐based heterocyclic thiones (thiols): 1‐methyl‐1H‐tetrazole‐5‐thiol (1‐MMTZ(H)); 4‐methyl‐4H‐1,2,4‐triazole‐3‐thiol (4‐MTT(H)); 1‐methyl‐1H‐imidazole‐2‐thiol (2‐MMI(H)); 5‐methyl‐1,3,4‐thiadiazole‐2‐thiol (5‐MMTD(H)); 1,3,4‐thiadiazole‐2‐dithiol (2,5‐DMTD(H)₂); and 4‐(4‐bromophenyl)thiazole‐2‐thiol (4‐BrMTD(H)). Reaction of BiPh₃ with 1‐MMTZ(H) produced the rare Bi^V thiolato complex [BiPh(1‐MMTZ)₄], which undergoes reduction in DMSO to give [BiPh(1‐MMTZ)₂{(1‐MMTZ(H)}₂]. Reactions with PhBiCl₂ or BiPh₃ generally produced monophenylbismuth thiolates, [BiPh(SR)₂]. The crystal structures of [BiPh(1‐MMTZ)₂{1‐MMTZ(H)}₂], [BiPh(5‐MMTD)₂], [BiPh{2,5‐DMTD(H)}₂(Me₂C?O)] and [Bi(4‐BrMTD)₃] were obtained. Evaluation of the bactericidal properties against M. smegmatis, S. aureus, MRSA, VRE, E. faecalis and E. coli showed complexes containing the anionic ligands 1‐ MMTZ, 4‐MTT and 4‐BrMTD to be most effective. The dithiolato dithione complexes [BiPh(4‐MTT)₂{4‐MTT(H)}₂] and [BiPh(1‐MMTZ)₂{1‐MMTZ(H)}₂] were most effective against all the bacteria: MICs 0.34 μM for [BiPh(4‐MTT)₂{4‐MTT(H)}₂] against VRE, and 1.33 μM for [BiPh(1‐MMTZ)₂{1‐MMTZ(H)}₂] against M. smegmatis and S. aureus. Tris‐thiolato Bi^III complexes were least effective overall. All complexes showed little or no toxicity towards mammalian COS‐7 cells at 20 μg mL^?1.     

Synthesis, Characterization and Antibacterial Activity of Some Transition Metal cis-3,7-dimethyl-2,6-octadiensemicarbazone Complexes

The synthesis and characterization of some transition metal cis-3,7-dimethyl-2,6-octadiensemicarbazone (CDOSC) complexes are reported. The ligand CDOSC yields: [ML₂ Cl₂] and [ML₂ Cl₂] Cl type complexes, where M = Cr^III, Mn^II, Fe^III, Co^II, Ni^II, Cu^II, Zn^II, Cd^II and Hg^II, L = CDOSC. Structures of the complexes were determined using elemental analysis, molar conductivity, magnetic measurements, i.r. and electronic, as well as n.m.r spectra. CDOSC acts as a bidentate ligand in all the complexes. All the newly synthesized metal complexes, as well as the ligand, were screened for their antibacterial activity. All the complexes exhibit strong inhibitory action against Gram (+) bacteria Staphylococcus aureus and Gram (−) bacteria Escherichia coli. The antibacterial activities of the complexes are stronger than those of the ligand CDOSC itself.     

Influence of Peripheral Substitution on the Magnetic Behavior of Single‐Ion Magnets Based on Homo‐ and Heteroleptic TbIII Bis(phthalocyaninate)

A series of homoleptic ([Tb^III(Pc)₂]) and heteroleptic ([Tb^III(Pc)(Pc′)]) Tb^III bis(phthalocyaninate) complexes that contain different peripheral substitution patterns (i.e., tert‐butyl or tert‐butylphenoxy groups) have been synthesized in their neutral radical forms and then reduced into their corresponding anionic forms as stable tetramethylammonium/tetrabutylammonium salts. All of these compounds were spectroscopically characterized and their magnetic susceptibility properties were investigated. As a general trend, the radical forms exhibited larger energy barriers for spin reversal than their corresponding reduced compounds. Remarkably, heteroleptic complexes that contain electron‐donor moieties on one of the two Pc ligands show higher effective barriers and blocking temperatures than their homoleptic derivatives. This result is assigned to the elongation of the N? Tb distances in the substituted macrocycle, which brings the terbium(III) ion closer to the unsubstituted Pc, thus enhancing the ligand‐field effect. In particular, heteroleptic [Tb^III(Pc)(Pc′)] complex 4 , which contains one octa(tert‐butylphenoxy)‐substituted Pc ring and one bare Pc ring, exhibits the highest effective barrier and blocking temperature for a single‐molecule magnet reported to date.     

Palladium(II)-Based Self-Assembled Heteroleptic Coordination Architectures: A Growing Family

Metal-driven self-assembly is one of the most effective approaches to lucidly design a large range of discrete 2D and 3D coordination architectures/complexes. Palladium(II)-based self-assembled coordination architectures are usually prepared by using suitable metal components, in either a partially protected form (PdL′) or typical form (Pd; charges are not shown), and designed ligand components. The self-assembled molecules prepared by using a metal component and only one type of bi- or polydentate ligand (L) can be classified in the homoleptic series of complexes. On the other hand, the less explored heteroleptic series of complexes are obtained by using a metal component and at least two different types of non-chelating bi- or polydentate ligands (such as L^a and L^b). Methods that allow the controlled generation of single, discrete heteroleptic complexes are less understood. A survey of palladium(II)-based self-assembled coordination cages that are heteroleptic has been made. This review article illustrates a systematic collection of such architectures and credible justification of their formation, along with reported functional aspects of the complexes. The collected heteroleptic assemblies are classified here into three sections: 1) [(PdL′)_m(L^a)_x(L^b)_y]-type complexes, in which the denticity of L^a and L^b is equal; 2) [(PdL′)_m(L^a)_x(L^b)_y]-type complexes, in which the denticity of L^a and L^b is different; and 3) [Pd_m(L^a)_x(L^b)_y]-type complexes, in which the denticity of L^a and L^b is equal. Representative examples of some important homoleptic architectures are also provided, wherever possible, to set a background for a better understanding of the related heteroleptic versions. The purpose of this review is to pave the way for the construction of several unique heteroleptic coordination assemblies that might exhibit emergent supramolecular functions.     

Synthesis,characterization, and antibacterial activity of new rare-earth ion complexes with unsymmetrical Schiff base ligand

A new unsymmetrical Schiff base ligand (H₂LLi) was synthesized using L-lysine, salicylaldehyde, and 2-hydroxy-1-naphthaldehyde. Three rare-earth ion complexes of this ligand, [REE(H₂L)(NO₃)]NO₃ · 2H₂O (REE = La, Sm, Ho), have been prepared and characterized by elemental analyses, IR spectra, UV spectra, TG-DTG, and molar conductance. The antibacterial activity of the ligand and its complexes are also studied. The antibacterial experiments indicate that this ligand and its complexes possess antibacterial activity against Escherichia coli, Staphylococcus aureus and Bacillus subtilis and the complexes have higher activity than that of the ligand. The article was submitted by the authors in English.     

Interaction between the antibacterial compound,oleuropein, and model membranes

Oleuropein, a secoiridoid glycoside extracted from the olive tree, Olea europaea L., has been described as showing antibacterial properties. However, the exact mechanism of these antimicrobial properties is not yet well understood. In the present study, we have studied the interaction of oleuropein with phosphatidylglycerol (PG) as a model membrane for Staphylococcus aureus (S. aureus) (Gram-positive bacteria) and phosphatidylethanolamine and Escherichia coli (E. coli) lipid extract as a model membrane for E. coli (Gram-negative bacteria). The study has been carried out using monolayers as model membranes and using kinetics at constant area and compression isotherms with Brewster angle microscopy (BAM) observations. The results show that oleuropein interacts in higher extent with PG monolayers, which is related with its stronger antibacterial effect against Gram-positive bacteria. The effects on the membrane are probably produced at the cell surface because oleuropein did not form stable mixed monolayers with the lipids assayed at the air/water interface.     

Synthesis,characterization and antimicrobial activity of zinc(II) ibuprofen complexes with nitrogen-based ligands

Metal carboxylate complexes possess different carboxylate coordination modes, e.g. monodentate, bidentate, and bridging bidentate. Five Zn(II) complexes were prepared and characterized in order to examine their coordination modes in addition to their biological activity. The syntheses were started by preparation of [Zn(ibup)₂(H₂O)₂] (1). Then, different nitrogen-donor ligands reacted with 1 to produce [Zn(ibup)₂(2-ampy)₂] (2), [Zn(ibup)(2-ammethylpy)] (3), [Zn(ibup)(2,2′-bipy)] (4), and [Zn₂(ibup)₄(2-methylampy)₂] (5) (ibup = ibuprofen, 2-ampy = 2-aminopyridine, 2-ammethylpy = 2-aminomethylpyridine, 2,2′-bipy = 2,2′-bipyridine, 2-methylampy = 2-(methylamino)pyridine). IR, ¹H NMR, ¹³C{¹H}-NMR and UV–vis spectroscopies were used for characterization. The crystal structures of 2 and 5 were determined by single-crystal X-ray diffraction. Investigation of in vitro antibacterial activities for the complexes against Gram-positive (Micrococcus luteus, Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis) bacteria were done using agar well-diffusion method. Complex 1 showed antibacterial activity against Gram-positive bacteria. Complexes 2 and 3 did not exhibit antibacterial activity. Complex 4 showed antibacterial activity and was chosen for further studies to determine the inhibition zone diameter for different concentrations and to set the minimum inhibitory concentration. The antibacterial activity against most of the bacteria was minimized as a result of the complexation of zinc ibuprofen with 2,2′-bipy in 4.     

Alaninyl variants of the marine natural product halocyamine A and their antibacterial properties

In an effort to explore the antibacterial potential of the marine natural product halocyamine A, a series of analogues including desbromo and alanine-substituted variants were synthesised and evaluated for biological activity against a panel of Gram-positive and –negative bacteria. The analogues were synthesised by a combination of solid-phase peptide synthesis and ruthenium complex/ytterbium triflate catalysed hydroamidation chemistry. Single alanine substitutions ([Ala¹]-halocyamine A and [Ala²]-halocyamine A) gave only modest increases in activity towards Gram-positive bacteria, while di-alaninyl variants exhibited more potent activity with MIC values of 12.5–50?μM towards the Gram-positive bacteria Staphylococcus aureus and Enterococcus faecalis. A lipophilic trityl-protected intermediate of [Ala²]-halocyamine was the most active against the Gram-negative bacterium Escherichia coli.     

Correlations and Contrasts in Homo‐ and Heteroleptic Cyclic (Alkyl)(amino)carbene‐Containing Pt0 Complexes

An improved synthetic route to homoleptic complex [Pt(CAAC^Me)₂] (CAAC=cyclic (alkyl)(amino)carbenes) and convenient routes to new heteroleptic complexes of the form [Pt(CAAC^Me)(PR₃)] are presented. Although the homoleptic complex was found to be inert to many reagents, oxidative addition and metal‐only Lewis pair (MOLP) formation was observed from one of the heteroleptic complexes. The spectroscopic, structural, and electrochemical properties of the zero‐valent complexes were explored in concert with density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) calculations. The homoleptic [Pt(CAAC)₂] and heteroleptic [Pt(CAAC)(PR₃)] complexes were found to be similar in their spectroscopic and structural properties, but their electrochemical behavior and reactivity differ greatly. The unusually strong color of the CAAC‐containing Pt⁰ complexes was investigated by TD‐DFT calculations and attributed to excitations into the LUMOs of the complexes, which are predominantly composed of bonding π interactions between Pt and the CAAC carbon atoms.