Molecular/polymeric metallaynes and related molecules: Solar cell materials and devices

The Many Facets of RuII(dppe)2 Acetylide Compounds

In this contribution, we describe the various research domains in which RuII alkynyl derivatives are involved. Their peculiar molecular properties stem from a strong and intimate overlap between the metal centered d orbitals and the π system of the acetylide ligands, resulting in plethora of fascinating properties such as strong and tunable visible light absorption with a strong MLCT character essential for sensing, photovoltaics, light-harvesting applications or non-linear optical properties. Likewise, the d/π mixing results in tunable redox properties at low potential due to the raising of the HOMO level, and making those compounds particularly suited to achieve redox switching of various properties associated to the acetylide conjugated ligand, such as photochromism, luminescence or magnetism, for charge transport at the molecular level and in field effect transistor devices, or charge storage for memory devices. Altogether, we show in this review the potential of RuII acetylide compounds, insisting on the molecular design and suggesting further research developments for this class of organometallic dyes, including supramolecular chemistry.

Synthesis of platinum(II)-complex end-tethered polymers: spectroscopic properties and nanostructured particles

Although metal-containing polymers have been widely studied as a novel class of functional soft materials, the microphase separation between polymeric segments and metal-ligand complexes has been less addressed, which is critical to control their structures and functions. To do this, short-chain polystyrenes (PSs) have been end-functionalized with nanosized square-planar platinum(II) complexes. The platinum(II)-comprising polymers were found to show significant luminescence enhancement in chloroform/methanol solvent mixtures upon increasing the methanol composition. By modulating both the PS length and solvent quality, various self-assembled morphologies formed controllably in the mixed solvents and typical examples include nanofibers, nanoellipsoids, and nanospheres. More interestingly, the inside structures of these polymer particles are shown to be lamellar with sub-10 nm spacings, wherein the PS blocks are alternatively aligned with the platinum(II) units. Such a luminescence enhancement and hierarchical nanostructured particles originate from a subtle combination of directional Pt(II)⋯Pt(II) and/or π-π stacking interactions between the platinum(II) units and the solvophobic effect between the PS blocks. This work suggests that by microphase separating polymer chains with nanosized metal-ligand complexes, metal-containing polymers can self-assemble to form sub-10 nm scale nanostructures showcasing desired properties and functions.

Bis-Alkynyl Complexes of Fe(III) Tetraaza Macrocycles─A Tale of Two Rings

Reported herein are new Fe bis-alkynyl complexes [Fe^III(L)(C₂R)₂]BPh₄ based on tetraimine macrocycle (L = HMTI = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene; 1a-1c; R = C₆H₅ (a), C₁₀H₉ (b), SiMe₃ (c)) and tetraamine macrocycle (L = HMC = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane; 2a-2c). These complexes have been characterized using single-crystal X-ray diffraction, electronic absorption spectroscopy, and cyclic and differential pulse voltammetry. Spectroelectrochemical studies of 1a and 2a allowed for investigation of the Fe^II oxidation state, which revealed a strong dependence on the nature of the macrocycle for both the energies of the Fe^II to C₂Ph metal-to-ligand charge transfer (MLCT) and the ν(C≡C). The ν(C≡C) was further influenced by the oxidation state, though sensitivity to the formal metal oxidation state was much higher in the case of 2a than in 1a. These findings are rationalized on the basis of the relative energies of the formally metal-centered orbitals via density functional theory calculations.

Heterometal Grafted Metalla-ynes and Poly(metalla-ynes): A Review on Structure-Property Relationships and Applications

Metalla-ynes and poly(metalla-ynes) have emerged as unique molecular scaffolds with fascinating structural features and intriguing photo-luminescence (PL) properties. Their rigid-rod conducting backbone with tunable photo-physical properties has generated immense research interests for the design and development of application-oriented functional materials. Introducing a second d- or f-block metal fragment in the main-chain or side-chain of a metalla-yne and poly(metalla-yne) was found to further modulate the underlying features/properties. This review focuses on the photo-physical properties and opto-electronic (O-E) applications of heterometal grafted metalla-ynes and poly(metalla-ynes).

Utilization of a Pt(ii) di-yne chromophore incorporating a 2,2'-bipyridine-5,5'-diyl spacer as a chelate to synthesize a green and red emitting d-f-d heterotrinuclear complex

A new heterotrinuclear (d-f-d) complex [Eu(btfa)₃1c] (btfa = 4,4,4-trifluoro-1-phenyl-1,3-butanedione and 1c = [(Ph)(Et₃P)₂Pt-C[triple bond, length as m-dash]C-R-C[triple bond, length as m-dash]C-Pt(Et₃P)₂(Ph)] (R = 2,2'-bipyridine-5,5'-diyl) has been synthesized by utilizing the N,N-donor sites of the organometallic chromophore. The complex was characterized by analytical and spectroscopic methods. Photophysical properties of the complex were analysed in detail using both steady-state and time-resolved emission and excitation spectroscopy. The optical absorption spectrum of the complex is dominated by the spin allowed π-π* transitions of the btfa and 1c units in the UV-visible region (200-418 nm) and thus is excitable over a wide range of wavelengths across the UV into the visible region of the electromagnetic spectrum. The complex displays typical red Eu(iii) emission when excited at 345 nm. However, it also shows green emission when excited at 464 nm and, thus could be an interesting candidate for full colour display applications. The change in the colour could be a result of the high value of the energy back-transfer rate (6.73 × 10⁵ s^-1) from the triplet state of the organometallic chromophore to the ⁵D₁ state of Eu(iii). Judd-Ofelt (J-O) intensity parameters (Ω₂ and Ω₄), radiative (A_R), non-radiative (A_R) decay rates and intrinsic quantum yield (Q) have been calculated.

A high molecular weight organometallic conjugated polymer incorporated with Hg(ii)

An organometallic conjugated polymer incorporated with Hg(ii) has an ultrahigh molecular weight and exhibits good mechanical properties.

Triphenylene-Derived Electron Acceptors and Donors on Ag(111): Formation of Intermolecular Charge-Transfer Complexes with Common Unoccupied Molecular States

Over the past years, ultrathin films consisting of electron donating and accepting molecules have attracted increasing attention due to their potential usage in optoelectronic devices. Key parameters for understanding and tuning their performance are intermolecular and molecule-substrate interactions. Here, the formation of a monolayer thick blend of triphenylene-based organic donor and acceptor molecules from 2,3,6,7,10,11-hexamethoxytriphenylene (HAT) and 1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile (HATCN), respectively, on a silver (111) surface is reported. Scanning tunneling microscopy and spectroscopy, valence and core level photoelectron spectroscopy, as well as low-energy electron diffraction measurements are used, complemented by density functional theory calculations, to investigate both the electronic and structural properties of the homomolecular as well as the intermixed layers. The donor molecules are weakly interacting with the Ag(111) surface, while the acceptor molecules show a strong interaction with the substrate leading to charge transfer and substantial buckling of the top silver layer and of the adsorbates. Upon mixing acceptor and donor molecules, strong hybridization occurs between the two different molecules leading to the emergence of a common unoccupied molecular orbital located at both the donor and acceptor molecules. The donor acceptor blend studied here is, therefore, a compelling candidate for organic electronics based on self-assembled charge-transfer complexes.

Limitations and Perspectives on Triplet-Material-Based Organic Photovoltaic Devices

Organic photovoltaic cells (OPVs) have attracted broad attention and become a very energetic field after the emergence of nonfullerene acceptors. Long-lifetime triplet excitons are expected to be good candidates for efficiently harvesting a photocurrent. Parallel with the development of OPVs based on singlet materials (S-OPVs), the potential of triplet materials as photoactive layers has been explored. However, so far, OPVs employing triplet materials in a bulk heterojunction have not exhibited better performance than S-OPVs. Here, the recent progress of representative OPVs based on triplet materials (T-OPVs) is briefly summarized. Based on that, the performance limitations of T-OPVs are analyzed. The shortage of desired triplet materials with favorable optoelectronic properties for OPVs, the tradeoff between long lifetime and high binding energy of triplet excitons, as well as the low charge mobility in most triplet materials are crucial issues restraining the efficiencies of T-OPVs. To overcome these limitations, first, novel materials with desired optoelectronic properties are urgently demanded; second, systematic investigation on the contribution and dynamics of triplet excitons in T-OPVs is necessary; third, close multidisciplinary collaboration is required, as proved by the development of S-OPVs.

Efficient as-cast semi-transparent organic solar cells with efficiency over 9% and a high average visible transmittance of 27.6%

Efficient as-cast ST-OSCs based on a trifluorinated polymer donor PBFTT and a tetrachlorinated NF-acceptor IT-4Cl were fabricated and a high efficiency of 9.1% was achieved under a high AVT of 27.6% in the photopic region.

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.