Functionalized Alkynylplatinum(II) Polypyridyl Complexes for Use as Sensitizers in Dye-Sensitized Solar Cells

Deep-blue phosphorescence from platinum(ii) bis(acetylide) complexes with sulfur-bridged dipyridyl ligands

New approaches to prepare rarer emitters such as those that are deep-blue are needed to advance OLED technologies. Here, we demonstrate that a series of new platinum(ii) bis(acetylide) complexes [Pt(N-N)(C[triple bond, length as m-dash]CPh)2] containing sulfur-bridged dipyridyl ligands (N-N) with various sulfur oxidation states: sulfide (S), sulfoxide (SO) and sulfone (SO2) give access to variable emission colors from green to deep-blue. Spectroscopic, electrochemical and computational studies show that mixed character excited states have energies which are significantly influenced by the oxidation state of sulfur and the presence of substituents. The sulfide and sulfoxide complexes are non-emissive in the solution state, while the sulfone complexes display 3MLCT/3LLCT excited-state yellow phosphorescence. In PMMA films the sulfide and sulfoxide complexes show intense deep-blue phosphorescence and green phosphorescence for the sulfone complexes, with photoluminescence quantum yields ranging from 0.35-0.91. Here we demonstrate the capability of changing the photophysical properties of these metal emitters by varying the oxidation state of sulfur to achieve intense deep-blue and green emitters.

Pathway control in metallosupramolecular polymerization of a monoalkynylplatinum(ii) terpyridine complex through competitive complex formation

Understanding the pathway complexity of supramolecular polymerization in biomimetic systems has been a challenging issue due to its importance in the development of rationally controlled materials and insight into self-assembly in nature. We herein report a kinetic trapping strategy as a new methodology on how to control the pathway of metallosupramolecular polymerization by employing secondary metal ions and/or ligands which form competitive complex species. For this, we proposed monoalkynylplatinum(ii) metalloligand (Pt-L1) derived from a bis(amideterpyridine) receptor with one unoccupied terpyridyl terminal as a coordination site for the secondary metal ion (Ag+ or Fe2+). The inherent pathway complexity intrinsic to the Pt-L1-anchored supramolecular polymerization has been modulated through the incorporation of Ag+ or Fe2+. During the supramolecular polymerization of Pt-L1 in the presence of Ag+ and Fe2+, the added secondary ligand bpy (4,4'-dimethyl-2,2'-bipyridine) or DA18C6 (1,14-diaza-18-crown-6) form complexes as kinetic species, thereby inhibiting spontaneous polymerizations. The supramolecular polymer (SP-I), with a spherical structure composed of Pt-L1 in the absence of metal ions as a kinetic product, did not transform into the thermodynamic product, namely supramolecular polymer (SP-III) with a left-handed fiber structure, due to a high energy barrier. However, the supramolecular polymer (SP-II) with a left-handed fiber structure, which was formed by Pt-L1 in the presence of AgNO3, converted to SP-III upon the addition of NaCl. Additionally, SP-II transformed into supramolecular polymer (SP-IV) upon the addition of Fe(BF4)2, through an on-pathway process. Both the morphological and emissive characteristics of the resulting supramolecular polymers can be fine-tuned via the Pt⋯Pt or Ag⋯Ag interactions as well as through the changes of the coordination geometry depending on the existing Ag+ or Fe2+ ions. The present results have important implications in expanding the scope of pathway complexity to produce a variety of products via kinetically controlled processes involving secondary metal ions and ligands.

Luminescent Platinum(II) Complexes with Stimuli-Responsive Flexible Lewis Pair Ligands: Spectroscopic and Computational Studies

A series of new luminescent bimetallic platinum(II) complexes with stimuli-responsive flexible Lewis pair (FlexLP) ligands are described. The FlexLP ligands consist of a dimesitylboron Lewis acid and diphenylphosphine oxide Lewis base which are in equilibrium between the unbound open form and the Lewis adduct, controlled by the hydrogen bond donating strength of the solvent. Spectroscopic techniques and density functional theory (DFT) calculations were used to interpret the photophysics of the platinum(II) complexes. All complexes exhibit tunable absorption in the region of 300-500 nm and green to orange photoluminescence, depending on the ratio of weak (THF) to strong (MeOH) hydrogen bond donating solvent employed. Spectroscopic and computational data shows that phosphine and peripheral acetylide ligands on the platinum(II) centers have limited influence on the emission energy, indicating the emission originates from the FlexLP-dominated fluorescence. Using time-resolved transient absorption spectroscopy it is shown that the complexes undergo intersystem crossing (ISC) to the triplet excited state upon photoexcitation, and the ISC efficiency is affected by the peripheral acetylide ligands. The triplet excited state lifetime can also be manipulated by the state of the FlexLP ligand, with the closed form complexes having longer lifetimes than the open form complexes.

Harnessing synergistic effects in GQD@Pt(II) nanocomposites for enhanced photovoltaic performance: a computational study

CONTEXT

The development of efficient solar energy conversion technologies is crucial for addressing global energy challenges and reducing reliance on fossil fuels. Platinum(II) complexes are promising materials for photovoltaic applications due to their strong light absorption and long-lived excited states. However, their narrow absorption in the visible spectrum and stability issues limit their performance. Combining platinum(II) complexes with graphene quantum dots (GQDs) can enhance photovoltaic performance by leveraging the complementary light harvesting and charge transfer characteristics of the two components. This study utilizes density functional theory (DFT) calculations to explore their electronic structures, charge transfer dynamics, and photoelectric performance. Specifically, it investigates the effects of incorporating different substituents, either electron-donating or electron-withdrawing, onto the fluorene motif of the Pt(II) complex. The findings reveal that combining GQDs with Pt(II) complexes extends light absorption into the UV range, enabling comprehensive solar utilization. Upon photoexcitation, electrons migrate between the GQD conduction band and the Pt(II) complex, stabilizing charges and enhancing extraction. Substituents significantly influence charge transfer dynamics: electron-withdrawing groups promote transfer to the GQD, while electron-donating groups encourage charge separation and delocalization. Nanocomposites featuring electron-donating substituents achieve the highest energy conversion efficiencies, with GQD@Pt(II)-NPh2 reaching 24.6%. This is attributed to improved light harvesting, efficient charge injection, and reduced recombination. These insights guide the rational design of GQD-Pt(II) nanocomposites, optimizing charge separation and transfer processes for enhanced photovoltaic performance. The computational approach employed here provides a robust tool for developing advanced materials in renewable energy technologies.

METHODS

The computational studies reported in this work were performed using the DFT approach, specifically employing the hybrid functional PBE0. The PBE0 functional's accuracy in describing electronic structures and excited-state properties is essential for understanding charge transfer processes, photoabsorption, and emission characteristics in metal-organic complexes. Geometry optimizations and time-dependent DFT (TD-DFT) calculations were carried out to investigate the properties of the nanocomposites. The effects of solvents were replicated using the conductor-like polarizable continuum model (CPCM). The charge transfer length (ΔL) and interfragment charge transfer (ΔQ) were calculated using the Multiwfn software package, and all calculations were performed using the BDF software package.

AIPE-active Pt(ii) complexes with a tunable triplet excited state: design, mechanochromism and application in anti-counterfeiting

A series of AIPE-active Pt(ii) complexes exhibit tunable triplet excited state properties, mechanochromic behavior and potential application in anti-counterfeiting.

Long-lived triplet excited state in a platinum(ii) perylene monoimide complex

We report the synthesis and solution based photophysical properties of a new Pt(ii)-terpyridine complex coupled to a perylene monoimide (PMI) chromophoric unit through an acetylene linkage. This structural arrangement resulted in quantitative quenching of the highly fluorescent PMI chromophore by introducing metal character into the lowest energy singlet state, thereby leading to the formation of a long-lived PMI-ligand localized triplet excited state (τ = 8.4 μs). Even though the phosphorescence from this triplet state was not observed, highly efficient quenching of this excited state by dissolved oxygen and the observation of singlet oxygen photoluminescence in the near-IR at 1270 nm initially pointed towards triplet excited state character. Additionally, the coincidence of the excited state absorbance difference spectra from the sensitized PMI ligand using a triplet donor and the Pt-PMI complex provided strong evidence for this triplet state assignment, which was further supported by TD-DFT calculations.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Temperature dependence of photophysical properties of a dinuclear C^N-cyclometalated Pt(ii) complex with an intimate Pt–Pt contact. Zero-field splitting and sub-state decay rates of the lowest triplet

A dinuclear Pt(ii) complexes exhibits an unusually large zero field splitting in its metal–metal-to-ligand charge transfer triplet excited state.

Directly Coupled Versus Spectator Linkers on Diimine PtII Acetylides-Change the Structure, Keep the Function?

Modification of light-harvesting units with anchoring groups for surface attachment often compromises light-harnessing properties. Herein, a series of [donor-acceptor-anchor] platinum(II) diimine (bis-)acetylides was developed in order to systematically compare the effect of conjugated versus electronically decoupled modes of attachment of protected anchoring groups on the photophysical properties of light-harvesting units. The first examples of "decoupled" phosphonate diimine Pt^II complexes are reported, and their properties are compared and contrasted to those of carboxylate analogues studied by a diversity of methods. Ultrafast time-resolved IR and transient absorption spectroscopy revealed that all complexes have a charge-transfer (CT) lowest excited state with lifetimes between 2 and 14 ns. Vibrational signatures and dynamics of CT states were identified; the assignment of electronic states and their vibrational origin was aided by TDDFT calculations. Ultrafast energy redistribution accompanied by structural changes was directly captured in the CT states. A significant difference between the structures of the electronic ground and CT excited states, as well as differences in the structural reorganisation in the complexes bearing directly attached or electronically decoupled anchoring groups, was discovered. This work demonstrates that decoupling of the anchoring group from the light-harvesting core by a saturated spacer is an easy approach to combine surface attachment with high reduction potential and ten times longer lifetime of the CT excited state of the light-absorbing unit, and retain electron-transfer photoreactivity essential for light-harvesting applications.

Platinum and Gold Complexes for OLEDs

Encouraging efforts on the design of high-performance organic materials and smart architecture during the past two decades have made organic light-emitting device (OLED) technology an important competitor for the existing liquid crystal displays. Particularly, the development of phosphorescent materials based on transition metals plays a crucial role for this success. Apart from the extensively studied iridium(III) complexes with d(6) electronic configuration and octahedral geometry, the coordination-unsaturated nature of d(8) transition metal complexes with square-planar structures has been found to provide intriguing spectroscopic and luminescence properties. This article briefly summarizes the development of d(8) platinum(II) and gold(III) complexes and their application studies in the fabrication of phosphorescent OLEDs. An in-depth understanding of the nature of the excited states has offered a great opportunity to fine-tune the emission colors covering the entire visible spectrum as well as to improve their photophysical properties. With good device engineering, high performance vacuum-deposited OLEDs with external quantum efficiencies (EQEs) of up to 30 % and solution-processable OLEDs with EQEs of up to 10 % have been realized by modifying the cyclometalated or pincer ligands of these metal complexes. These impressive demonstrations reveal that d(8) metal complexes are promising candidates as phosphorescent materials for OLED applications in displays as well as in solid-state lighting in the future.

Terpyridine and Quaterpyridine Complexes as Sensitizers for Photovoltaic Applications

Terpyridine and quaterpyridine-based complexes allow wide light harvesting of the solar spectrum. Terpyridines, with respect to bipyridines, allow for achieving metal-complexes with lower band gaps in the metal-to-ligand transition (MLCT), thus providing a better absorption at lower energy wavelengths resulting in an enhancement of the solar light-harvesting ability. Despite the wider absorption of the first tricarboxylate terpyridyl ligand-based complex, Black Dye (BD), dye-sensitized solar cell (DSC) performances are lower if compared with N719 or other optimized bipyridine-based complexes. To further improve BD performances several modifications have been carried out in recent years affecting each component of the complexes: terpyridines have been replaced by quaterpyridines; other metals were used instead of ruthenium, and thiocyanates have been replaced by different pinchers in order to achieve cyclometalated or heteroleptic complexes. The review provides a summary on design strategies, main synthetic routes, optical and photovoltaic properties of terpyridine and quaterpyridine ligands applied to photovoltaic, and focuses on n-type DSCs.

Exploring excited states of Pt(II) diimine catecholates for photoinduced charge separation

The intense absorption in the red part of the visible range, and the presence of a lowest charge-transfer excited state, render Platinum(II) diimine catecholates potentially promising candidates for light-driven applications. Here, we test their potential as sensitisers in dye-sensitised solar cells and apply, for the first time, the sensitive method of photoacoustic calorimetry (PAC) to determine the efficiency of electron injection in the semiconductor from a photoexcited Pt(II) complex. Pt(II) catecholates containing 2,2′-bipyridine-4,4′-di-carboxylic acid (dcbpy) have been prepared from their parent iso-propyl ester derivatives, complexes of 2,2′-bipyridine-4,4′-di-C(O)OiPr, (COOiPr)2bpy, and their photophysical and electrochemical properties studied. Modifying diimine Pt(II) catecholates with carboxylic acid functionality has allowed for the anchoring of these complexes to thin film TiO2, where steric bulk of the complexes (3,5-di(t)Bu-catechol vs. catechol) has been found to significantly influence the extent of monolayer surface coverage. Dye-sensitised solar cells using Pt(dcbpy)((t)Bu2Cat), 1a, and Pt(dcbpy)(pCat), 2a, as sensitisers, have been assembled, and photovoltaic measurements performed. The observed low, 0.02–0.07%, device efficiency of such DSSCs is attributed at least in part to the short excited state lifetime of the sensitisers, inherent to this class of complexes. The lifetime of the charge-transfer ML/LLCT excited state in Pt((COO(I)Pr)2bpy)(3,5-di-(t)Bu-catechol) was determined as 250 ps by picosecond time-resolved infrared spectroscopy, TRIR. The measured increase in device efficiency for 2a over 1a is consistent with a similar increase in the quantum yield of charge separation (where the complex acts as a donor and the semiconductor as an acceptor) determined by PAC, and is also proportional to the increased surface loading achieved with 2a. It is concluded that the relative efficiency of devices sensitised with these particular Pt(II) species is governed by the degree of surface coverage. Overall, this work demonstrates the use of Pt(diimine)(catecholate) complexes as potential photosensitizers in solar cells, and the first application of photoacoustic calorimetry to Pt(II) complexes in general.

Synthesis, characterization, photophysics, and anion binding properties of platinum(ii) acetylide complexes with urea group

The relationship between the structure and anion-binding ability of platinum(ii) acetylide complexes with urea group has been studied.

Synthesis, photovoltaic performances and TD-DFT modeling of push-pull diacetylide platinum complexes in TiO2 based dye-sensitized solar cells

In this joint experimental-theoretical work, we present the synthesis and optical and electrochemical characterization of five new bis-acetylide platinum complex dyes end capped with diphenylpyranylidene moieties, as well as their performances in dye-sensitized solar cells (DSCs). Theoretical calculations relying on Time-Dependent Density Functional Theory (TD-DFT) and a range-separated hybrid show a very good match with experimental data and allow us to quantify the charge-transfer character of each compound. The photoconversion efficiency obtained reaches 4.7% for 8e (see TOC Graphic) with the tri-thiophene segment, which is among the highest efficiencies reported for platinum complexes in DSCs.