Platinum(II) Complexes of N∧C∧N-Coordinating 1,3-Bis(2-pyridyl)benzene Ligands: Thiolate Coligands Lead to Strong Red Luminescence from Charge-Transfer States

Photodynamic Effect of Amphiphilic N∧C∧N-Coordinated Platinum(II) Complexes in Human Umbilical Vein Endothelial Cells

Here, we report a photodynamic therapy (PDT) photosensitizer of N∧C∧N-coordinated Pt(II) complexes: [Pt(L)(solv)]+ (HL = 1,3-(2-dipyridyl)benzene) and [Pt(L)]+@HSA, which is the Pt(II) complex encapsulated in human serum albumin (HSA). The quantum yield of singlet oxygen production for [Pt(L)(solv)]+ is more than 50%, while that for [Pt(L)]+@HSA is much lower. Photoimages of human umbilical vein endothelial cells (HUVECs) treated with the Pt(II) complexes suggest that [Pt(L)(solv)]+ is delocalized in the entire cell after the fast uptake by diffusion and [Pt(L)]+@HSA is taken up by endocytosis and localized on organelles and the cell membrane. [Pt(L)(solv)]+ shows high photocytotoxicity for HUVECs, while [Pt(L)]+@HSA does not show photocytotoxicity.

Cyclometalated luminescent platinum(II) complexes of dissymmetrical 2,2':4',2''-terpyridine and its self-assembled dimer presenting Pt-Ag dative bonds

A series of cyclometalated (N^C^N) Pt(II)-platinum complexes featuring a terpyridine ligand with a non-coordinating nitrogen atom and a Pt-C bond was synthesized. In the presence of Ag+, the bis(isonitrile)Pt(II) complex formed a remarkable self-assembled helicoidal dimer stabilized by coordination of Ag(I) and metallophilic Pt-Ag interactions. Its assembly was observed in the solid state and maintained in solution. All complexes show strong luminescence and multiple emitting states, which could be rationalized based on solid state X-ray structures and coordinating environment.

Pt-S Bond-Enabled Temperature-Dependent Phosphorescence in S-Heteroaryl Tetradentate Pt(S^C^N^O) Complexes

This study presents the rare examples of S-heteroaryl tetradentate Pt(S^C^N^O) luminescent complexes (PtSZ and PtSZtBu) containing a Pt-S bond. The presence of the Pt-S bond allows the novel Pt(S^C^N^O) complexes to exhibit temperature-dependent phosphorescent emission behavior. The PtSZtBu exhibits dual-emission phenomena and biexponential transient decay spectra above 250 K, indicating the presence of two minimal excited states in the potential energy surface (PES) of the T1 state. Through complementary experimental and computational studies, we have identified changes in orbital composition between Pt(dxy)-S(px) and Pt(dyz)-S(pz) in excited states with increasing temperature. This results in two energy minima, enabling the excited states to decay selectively and radiatively at different temperatures. Consequently, this leads to remarkable steady-state and transient emission spectra changes. Our work not only provides valuable insights for the development of novel Pt-S bond-based tetradentate Pt(II) complexes but also enhances our understanding of the distinctive properties governed by the Pt-S bond.

Structural modifications to platinum(II) pincer complexes resulting in changes in their vapochromic and solvatochromic properties

There is a need to develop rapidly responsive chemical sensors for the detection of low concentrations of volatile organic solvents (VOCs). Platinum pincer complexes have shown promise as sensors because of their colours and vapochromic and solvatochromic properties, that may be related to the non-covalent interactions between the pincer complexes and the guest VOCs. Here we report an investigation into a series of Pt(II) complexes based on the 1,3-di(pyridine)benzene tridentate (N⁁C⁁N) skeleton with the formula [Pt(N⁁C(R)⁁N)(CN)] (R = C(O)Me 2, C(O)OEt 3, C(O)OPh 4) with the fourth coordination site occupied by a cyanide ligand. Solid-state samples of the complexes have been tested with a range of volatiles including methanol, ethanol, acetone, dichloromethane and water, and while 2 displays thermochromism, 3 and 4 display rapidly reversible vapochromism and solvatochromism. These results are correlated with X-ray powder and single crystal X-ray structural data including an assessment of the crystal packing and the void space in the crystalline space. The cyanide ligand and the R substituents are involved in hydrogen bonding that creates the voids within the structures and interact with the solvent molecules that influence the Pt⋯Pt separation in the crystalline state.

Competition between N,C,N-Pincer and N,N-Chelate Ligands in Platinum(II)

Replacement of the chloride ligand of PtCl{κ3-N,C,N-[py-C6HR2-py]} (R = H (1), Me (2)) and PtCl{κ3-N,C,N-[py-O-C6H3-O-py]} (3) by hydroxido gives Pt(OH){κ3-N,C,N-[py-C6HR2-py]} (R = H (4), Me (5)) and Pt(OH){κ3-N,C,N-[py-O-C6H3-O-py]} (6). These compounds promote deprotonation of 3-(2-pyridyl)pyrazole, 3-(2-pyridyl)-5-methylpyrazole, 3-(2-pyridyl)-5-trifluoromethylpyrazole, and 2-(2-pyridyl)-3,5-bis(trifluoromethyl)pyrrole. The coordination of the anions generates square-planar derivatives, which in solution exist as a unique species or equilibria between isomers. Reactions of 4 and 5 with 3-(2-pyridyl)pyrazole and 3-(2-pyridyl)-5-methylpyrazole provide Pt{κ3-N,C,N-[py-C6HR2-py]}{κ1-N1-[R'pz-py]} (R = H; R' = H (7), Me (8). R = Me; R' = H (9), Me (10)), displaying κ1-N1-pyridylpyrazolate coordination. A 5-trifluoromethyl substituent causes N1-to-N2 slide. Thus, 3-(2-pyridyl)-5-trifluoromethylpyrazole affords equilibria between Pt{κ3-N,C,N-[py-C6HR2-py]}{κ1-N1-[CF3pz-py]} (R = H (11a), Me (12a)) and Pt{κ3-N,C,N-[py-C6HR2-py]}{κ1-N2-[CF3pz-py]} (R = H (11b), Me (12b)). 1,3-Bis(2-pyridyloxy)phenyl allows the chelating coordination of the incoming anions. Deprotonations of 3-(2-pyridyl)pyrazole and its substituted 5-methyl counterpart promoted by 6 lead to equilibria between Pt{κ3-N,C,N-[pyO-C6H3-Opy]}{κ1-N1-[R'pz-py]} (R' = H (13a), Me (14a)) with a κ-N1-pyridylpyrazolate anion, keeping the pincer coordination of the di(pyridyloxy)aryl ligand, and Pt{κ2-N,C-[pyO-C6H3(Opy)]}{κ2-N,N-[R'pz-py]} (R' = H (13c), Me (14c)) with two chelates. Under the same conditions, 3-(2-pyridyl)-5-trifluoromethylpyrazole generates the three possible isomers: Pt{κ3-N,C,N-[pyO-C6H3-Opy]}{κ1-N1-[CF3pz-py]} (15a), Pt{κ3-N,C,N-[pyO-C6H3-Opy]}{κ1-N2-[CF3pz-py]} (15b), and Pt{κ2-N,C-[pyO-C6H3(Opy)]}{κ2-N,N-[CF3pz-py]} (15c). The N1-pyrazolate atom produces a remote stabilizing effect on the chelating form, pyridylpyrazolates being better chelate ligands than pyridylpyrrolates. Accordingly, reactions of 4-6 with 2-(2-pyridyl)-3,5-bis(trifluoromethyl)pyrrole yield Pt{κ3-N,C,N-[py-C6HR2-py]}{κ1-N1-[(CF3)2C4(py)HN]} (R = H (16), Me (17)) or Pt{κ3-N,C,N-[pyO-C6H3-Opy]}{κ1-N1-[(CF3)2C4(py)HN]} (18), displaying κ1-N1-pyrrolate coordination. Complexes 7-10 are efficient green phosphorescent emitters (488-576 nm). In poly(methyl methacrylate) (PMMA) films and in dichloromethane, they experience self-quenching, due to molecular stacking. Aggregation occurs through aromatic π-π interactions, reinforced by weak platinum-platinum interactions.

Platinum(IV) Complexes with Tridentate, NNC-Coordinating Ligands: Synthesis, Structures, and Luminescence

Platinum(II) complexes of NNC-cyclometalating ligands based on 6-phenyl-2,2'-bipyridine (HL¹) have been widely investigated for their luminescence properties. We describe how PtL¹Cl and five analogues with differently substituted aryl rings, PtL^2-6Cl, can be oxidized with chlorine and/or iodobenzene dichloride to generate Pt(IV) compounds of the form Pt(NNC-Lⁿ)Cl₃ (n = 1-6). The molecular structures of several of them have been determined by X-ray diffraction. These PtLⁿCl₃ compounds react with 2-arylpyridines to give a new class of Pt(IV) complex of the form [Pt(NNC)(NC)Cl]⁺. Elevated temperatures are required, and the reaction is accompanied by competitive reduction processes and generation of side-products; however, four examples of such complexes have been isolated and their molecular structures determined. Reaction of PtL¹Cl₃ with HL¹ similarly generates [Pt(NNC-L¹)₂]²⁺, which we believe to be the first example of a bis-tridentate Pt(IV) complex. The lowest-energy bands in the UV-vis absorption spectra of all the PtLⁿCl₃ compounds are displaced to higher energy relative to the Pt(II) precursors, but they red-shift with the electron richness of the aryl ring, consistent with predominantly ¹[π_Ar → π*_NN] character to the pertinent excited state. A similar trend is observed for the [Pt(NNC)(NC)Cl]⁺ complexes. They display phosphorescence in solution at room temperature, centered around 500 nm for [PtL¹(ppy)Cl]⁺ and [Pt(L¹)₂]²⁺, and 550 nm for methoxy-substituted derivatives. The lifetimes are in the microsecond range, rising to hundreds of microseconds at 77 K, consistent with triplet excited states of primarily ³[π_Ar → π*_NN] character with relatively little participation of the metal.

Near-infrared electroluminescence beyond 940 nm in Pt(N^C^N)X complexes: influencing aggregation with the ancillary ligand X

We present a study of aggregate excited states formed by complexes of the type Pt(N^C^N)X, where N^C^N represents a tridentate cyclometallating ligand, and X = SCN or I. These materials display near-infrared (NIR) photoluminescence in film and electroluminescence in NIR OLEDs with λ max EL = 720-944 nm. We demonstrate that the use of X = SCN or I modulates aggregate formation compared to the parent complexes where X = Cl. While the identity of the monodentate ligand affects the energy of Pt-Pt excimers in solution in only a subtle way, it strongly influences aggregation in film. Detailed calculations on aggregates of different sizes support the experimental conclusions from steady-state and time-resolved luminescence studies at variable temperatures. The use of X = I appears to limit aggregation to the formation of dimers, while X = SCN promotes the formation of larger aggregates, such as tetramers and pentamers, leading in turn to NIR photo- and electroluminescence > 850 nm. A possible explanation for the contrasting influence of the monodentate ligands is the lesser steric hindrance associated with the SCN group compared to the bulkier I ligand. By exploiting the propensity of the SCN complexes to form extended aggregates, we have prepared an NIR-emitting OLED that shows very long wavelength electroluminescence, with λ max EL = 944 nm and a maximum EQE = 0.3 ± 0.1%. Such data appear to be unprecedented for a device relying on a Pt(ii) complex aggregate as the emitter.

A Novel Class of Cyclometalated Platinum(II) Complexes for Solution-Processable OLEDs

Substitution of the chlorido ligand of cyclometalated [Pt (5-R-1,3-di(2-pyridyl) benzene)Cl] (R = methyl, mesityl, 2-thienyl, or 4-diphenylamino-phenyl) by 4-phenylthiazole-2-thiolate leads to related thiolato complexes, which were fully characterized. Their photophysical properties were determined in degassed dichloromethane solution. The emission color of the novel complexes can be easily tuned by the nature of the substituents on the terdentate ligand, as is the case for the parent chlorido complexes. Their luminescence Quantum Yield is high, with that of the compounds with the 2-thienyl or 4-diphenylamino-phenyl substituents being much higher than that of the related chloride complexes. The platinum complex with the cyclometalated 5-(2-thienyl)-1,3-di(2-pyridyl) benzene was used as the emitter for the fabrication of a yellow solution-processable OLED.

Twist to Boost: Circumventing Quantum Yield and Dissymmetry Factor Trade-Off in Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) enables promising applications in asymmetric photonics. However, the performances of CPL molecules do not yet meet the requirements of these applications. The shortcoming originates from the trade-off in CPL between the photoluminescence quantum yield (PLQY) and the photoluminescence dissymmetry factor (g_PL). In this study, we developed a molecular strategy to circumvent this trade-off. Our approach takes advantage of the strong propensity of [Pt(N^C^N)Cl], where the N^C^N ligand is 1-(2-oxazoline)-3-(2-pyridyl)phenylate, to form face-to-face stacks. We introduced chiral substituents, including (S)-methyl, (R)- and (S)-isopropyl, and (S)-indanyl groups, into the ligand framework. This asymmetric control induces torsional displacements that give homohelical stacks of the Pt(II) complexes. X-ray single-crystal structure analyses for the (S)-isopropyl Pt(II) complex reveal the formation of a homohelical dimer with a Pt···Pt distance of 3.48 Å, which is less than the sum of the van der Waals radii of Pt. This helical stack elicits the metal-metal-to-ligand charge-transfer (MMLCT) transition that exhibits strong chiroptical activity due to the electric transition moment making an acute angle to the magnetic transition moment. The PLQY and g_PL values of the MMLCT phosphorescence emission of the (S)-isopropyl Pt(II) complex are 0.49 and 8.4 × 10^-4, which are improved by factors of ca. 6 and 4, respectively, relative to the values of the unimolecular emission (PLQY, 0.078; g_PL, 2.4 × 10^-4). Our photophysical measurements for the systematically controlled Pt(II) complexes reveal that the CPL amplifications depend on the chiral substituent. Our investigations also indicate that excimers are not responsible for the enhanced chiroptical activity. To demonstrate the effectiveness of our approach, organic electroluminescence devices were fabricated. The MMLCT emission devices were found to exhibit simultaneous enhancements in the external quantum efficiency (EQE, 9.7%) and the electroluminescence dissymmetry factor (g_EL, 1.2 × 10^-4) over the unimolecular emission devices (EQE, 5.8%; g_EL, 0.3 × 10^-4). These results demonstrate the usefulness of using the chiroptically active MMLCT emission for achieving an amplified CPL.

Reversible stimuli-responsive chromism of a cyclometallated platinum(II) complex

We report the reversible chromism and luminescence of a cyclometalated platinum(ii) complex that forms dimers, with close PtPt interactions that can be modulated by solvent and temperature. The precise reversible control may be exploited in future stimuli-responsive chemosensing or optoelectronic devices.

Macrocyclic Metal Complexes Bearing Rigid Polyaromatic Ligands: Synthesis and Catalytic Activity

We synthesised palladium and platinum complexes possessing cyclic and acyclic pincer-type polyaromatic ligands and investigated their structural effect on the catalysis. The pincer-type bis(6-arylpyridin-2-yl)benzene skeleton was constructed via Kröhnke pyridine synthesis under transition metal-free conditions on gram-scale quantity. Ligand structure significantly influenced catalytic activity toward the platinum-catalysed hydrosilylation of diphenyl acetylenes, despite the ligand-independence of the conformations and electronic properties of these complexes.

A cyclometalated trinuclear Ir(iii)/Pt(ii) complex as a luminescent probe for histidine-rich proteins

A trinuclear luminescent organometallic Pt–Ir–Pt complex acts as an efficient protein staining agent due to reversible binding to histidine-rich proteins.

Determination of uric acid in serum using an optical sensor based on binuclear Pd(II) 2-pyrazinecarboxamide-bipyridine doped in a sol gel matrix

A new highly green luminescent binuclear palladium 2-pyrazinecarboxamide-bipyridine complex [Pd(pyc)(bpy)] was prepared and characterized. The binuclear Pd(pyc)(bpy) complex doped in sol-gel matrix has a strong luminescence intensity at 547 nm with λ_ex = 330 nm in water The method depends on the quenching of the luminescence intensity of the binuclear Pd(pyc)(bpy) complex at 547 nm by different concentrations of uric acid. The remarkable quenching of the luminescence intensity of the binuclear Pd(pyc)(bpy) complex, doped in a sol-gel matrix, by uric acid was successfully used for the determination of uric acid in serum samples of patients with hypouricemia disease. The calibration plot was achieved over the concentration 3.9 × 10^-9 to 1.2 × 10^-4 mol L^-1uric acid with a correlation coefficient of 0.9 and a detection limit of 1.8 × 10^-10 mol L^-1. The method was used satisfactorily for the assessment of the uric acid in a number of serum samples collected from various patients with Hypouricemia disease.

Synthesis, Mesomorphism, and Photophysics of 2,5-Bis(dodecyloxyphenyl)pyridine Complexes of Platinum(IV)

It has been shown for the first time that the Pt^IV complex cis-[Pt(N^C-tolpy)₂ Cl₂ ] (tolpy=2-(4-tolyl)pyridinyl) can be prepared in a one-pot reaction from K₂ [PtCl₄ ], although analogous complexes containing 2,5-bis(4-dodecyloxyphenyl)pyridine (=HL) could be prepared using existing routes. The resulting complexes cis-[Pt(N^C-L)₂ Cl₂ ] are liquid crystals and small-angle X-ray scattering suggests formation of a lamellar mesophase. Surprisingly, heating [Pt(κ² -N^C-L)₂ Cl(κ¹ -N^C-LH)] also leads to a mesomorphic compound, which results from thermally induced oxidation to cis-[Pt(N^C-L)₂ Cl₂ ] and what is presumed to be another geometric isomer of the same formula. The Pt^IV complexes are quite strongly luminescent in deoxygenated solution, with φ≈10 % and show vibrationally structured emission spectra, λ_max (0,0)=532 nm, strongly displaced to the red compared to cis-[Pt(N^C-tolpy)Cl₂ ]. Long luminescence lifetimes of 230 μs are attributed to a lower degree of metal character in the excited state accompanying the extension of conjugation in the ligand. There is no significant difference between the emission properties of the bromo- and chloro-complexes, in contrast with the known complexes cis-[Pt(N^C-ppy)X₂ ], where the quantum yield for X=Br is some 30 times lower than for X=Cl (ppyH=2-phenylpyridine). The lower energy of the excited state in the new complexes probably ensures that deactivating LLCT/LMCT states remain thermally inaccessible, even when X=Br.

The influence of thiolate ligands on the luminescence properties of cycloplatinated(ii) complexes

Complexes [Pt(C^{^}N)(PPh₃)Cl] (C^{^}N = bzq (7,8-benzoquinolinyl, A) and ppy (2-phenylpyridinyl, B)) were reacted with various thiolate ligands to afford complexes [Pt(C^{^}N)(PPh₃)(κ¹-S-SR)], C^{^}N = bzq, R = SPh (thiophenolate, 1a); C^{^}N = ppy, R = SPh (1b); C^{^}N = bzq, R = Spy (pyridine-2-thiolate, 2a); C^{^}N = ppy, R = Spy (2b); C^{^}N = bzq, R = SpyN (pyrimidine-2-thiolate, 3a); C^{^}N = ppy, R = SpyN (3b). Complexes 1-3 were characterized by NMR spectroscopy, and the solid-state structures of 1a and 2a were determined by X-ray diffraction methods. Replacing a chloride ligand with electron-rich thiolates changes the lowest energy singlet and triplet excited states to the ones that feature charge transfer from the thiolate (mixed with some metal character) to the C^{^}N ligand, which was supported by TD-DFT calculations. All complexes are emissive at 298 K in the solid state except 2b and 3b, which are emissive only at 77 K having a less rigid structure compared to others. The emission of 1a and 1b originates from a low-energy excited state of d_Pt/π_SR → π*_C^N while 3a exhibits a ³LC/³MLCT transition. For 1a and 1b, the radiative rate and the quantum efficiency are higher in a rigid environment such as a solid compared to a polymer and solution. Decreasing the rigidity of the environment leads to a flexibility of rotation of the -SR around the axis of the Pt-S bond. So the geometry can be easily changed after radiation and the lowest lying triplet excited state would have the effective contribution of the dd* transition, which opens a nonradiative pathway at room temperature.

Theoretical study of the substituent effect controlling the radiative and non-radiative decay processes of platinum(ii) complexes

Six platinum complexes bearing different electron-withdrawing groups (-CN, -NO₂, -o-carborane, -SF₅ and -CF₂CF₂CF₃) have been designed to explore the electron-withdrawing capability and the conjugative effect of the substituents, and density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been performed to determine their electronic structures and phosphorescent properties. Three factors, including the oscillator strength μ(S_n) for S₀-S_n excitations, the energy gap between the triplet and singlet states ΔE(S_n-T₁) and the spin-orbital coupling 〈T₁|Ĥ_SOC|S_n〉, have been calculated to analyze the radiative processes. In addition, temperature-independent, temperature-dependent and triplet-triplet annihilation (TTA) have been analyzed to determine the non-radiative decay processes. Introducing strong electron-withdrawing groups into phosphorescent transition-metal complexes has a significant impact on the phosphorescent properties and some regularity besides the inductive effect (the electron-withdrawing capability) and the conjugative effect of the substituents. The stronger electron-withdrawing capability and smaller conjugative effect can give rise to blue-shifted emission behavior and give larger radiative decay rate constants. The results demonstrate that complex 4 (-NO₂ substituted) and complex 2 (-o-carborane) are possible candidates for blue-emitting materials.

Rhenium tricarbonyl complexes with arenethiolate axial ligands

Pyta and Tapy-based [Re(N^N)(CO)₃X] complexes with para-substituted benzenethiolates as axial ligand are reported along with their electrochemical and photophysical properties.

Phosphorescent Pt(ii) complexes bearing a monoanionic C^N^N luminophore and tunable ancillary ligands

A new monoanionic pincer luminophore is presented, yielding phosphorescent Pt(ii) complexes bearing a neutral 1,2,3-triazole ring introduced via click chemistry. The overall charge, intermolecular interactions and excited state properties can be manipulated and controlled.

Highly efficient electroluminescent PtII ppy-type complexes with monodentate ligands

Functional Pt^II ppy-type complexes (ppy = 2-phenylpyridine anion) with pyridine and chloride monodentate ligands are prepared, which show high electroluminescence efficiencies.

A new approach to the effects of isocyanide (CN-R) ligands on the luminescence properties of cycloplatinated(ii) complexes

Cycloplatinated complexes bearing isocyanides were prepared and characterized. The complexes exhibited strong luminescence while the nature of R substituents in isocyanides affected the luminescence characteristics.

New N^C^N-coordinated Pd(ii) and Pt(ii) complexes of a tridentate N-heterocyclic carbene ligand featuring a 6-membered central ring: synthesis, structures and luminescence

Photoluminescent pincer-like Pd(ii) and Pt(ii) complexes with a rare tridentate N^C^N ligand with a six membered NHC central core are described. Solid-state packing exhibits M(ii)⋯M(ii) and π–π interactions.

Developing strongly luminescent platinum(IV) complexes: facile synthesis of bis-cyclometalated neutral emitters

A straightforward, one-pot procedure has been developed for the synthesis of bis-cyclometalated chloro(methyl)platinum(IV) complexes with a wide variety of heteroaromatic ligands of the 2-arylpyridine type. The new compounds exhibit phosphorescent emissions in the blue to orange colour range and represent the most efficient Pt(IV) emitters reported to date, with quantum yields up to 0.81 in fluid solutions at room temperature.

HOMO-LUMO energy gap control in platinum(II) biphenyl complexes containing 2,2'-bipyridine ligands

A series of platinum(ii) biphenyl 2,2'-bipyridine complexes containing electron-donating and electron-withdrawing moieties on the 4 and 4' positions of the bipyridine ligand exhibit emission from excited states in the 600 nm region of the spectrum upon excitation in the metal-to-ligand charge transfer transition located near 450 nm. These complexes are distorted from planarity based on both single crystal structure determinations and density functional theory (DFT) calculations of isolated molecules in acetonitrile. The DFT also reveals the geometry of the lowest-lying triplet state (LLTS) of each complex that is important for emission behavior. The LLTS are assigned based on the electron spin density distributions and correlated with the singlet excited states to understand the mechanism of electronic excitation and relaxation. Time-dependent DFT calculations are performed to compute the singlet excited state energies of these complexes so as to help interpret their UV-Vis absorption spectra. Computational and experimental results, including absorption and emission energy maxima, electrochemical reduction potentials, LLTS, singlet excited states, and LUMO and HOMO energies, exhibit linear correlations with the Hammett constants for para-substituents σp. These correlations are employed to screen complexes that have not yet been synthesized. The correlation analysis indicates that the electronic structure and the HOMO-LUMO energy gap in Pt(ii) complexes can be effectively controlled using electron-donating and electron-withdrawing moieties covalently bonded to the ligands. The information presented in this paper provides a better understanding of the fundamental electronic and thermodynamic behavior of these complexes and could be used to design systems with specific applications.