Negative polaron and triplet exciton diffusion in organometallic "molecular wires"

Long-lived triplet charge-separated state in naphthalenediimide based donor-acceptor systems

1,4,5,8-Naphthalenediimides (NDIs) are widely used motifs to design multichromophoric architectures due to their ease of functionalisation, their high oxidative power and the stability of their radical anion. The NDI building block can be incorporated in supramolecular systems by either core or imide functionalization. We report on the charge-transfer dynamics of a series of electron donor-acceptor dyads consisting of a NDI chromophore with one or two donors linked at the axial, imide position. Photo-population of the core-centred π-π* state is followed by ultrafast electron transfer from the electron donor to the NDI. Due to a solvent dependent singlet-triplet equilibrium inherent to the NDI core, both singlet and triplet charge-separated states are populated. We demonstrate that long-lived charge separation in the triplet state can be achieved by controlling the mutual orientation of the donor-acceptor sub-units. By extending this study to a supramolecular NDI-based cage, we also show that the triplet charge-separation yield can be increased by tuning the environment.

Compartmentalization-induced phosphorescent emission enhancement and triplet energy transfer in aqueous medium

Triplet energy transfer occurs frequently in natural photosynthetic organisms to protect against photo-oxidative stress. For artificial light-harvesting systems, several challenges need to be addressed to realize triplet energy transfer especially in aqueous medium. Specifically, the phosphors should be shielded from water and molecular oxygen, which facilitate to maintain intense emission intensity. Moreover, the donor‒acceptor phosphors should be organized in close proximity, yet simultaneously avoiding direct homo- and hetero-interactions to minimize the potential energy losses. Herein an effective strategy has been developed to meet these requirements, by employing a rod-coil amphiphile as the compartmentalized agent. It renders synergistic rigidifying and hydrophobic shielding effects, giving rise to enhanced phosphorescent emission of the platinum(II) complexes in aqueous environment. More importantly, the donor‒acceptor platinum(II) phosphors feature ordered spatial organization in the ternary co-assembled system, resulting in high light-harvesting efficiency. Therefore, the compartmentalization strategy represents an efficient approach toward color-tunable phosphorescent nanomaterials.

Synthesis of Re(I) Rings Comprising Different Re(I) Units and Their Light-Harvesting Abilities

Trimethylamine N-oxide (Me₃NO) could selectively remove only one CO ligand from fac-[Re(N^N)(CO)₃(PR₂R')]⁺ (N^N = diimine ligand), whereby only the CO ligand in the trans position to the phosphorus ligand was selectively removed to give cis,trans-[Re^I(N^N)(CO)₂(PR₂R')(L)] ⁿ⁺ in good yields. This decarbonylation reaction using Me₃NO was found to be especially useful for synthesizing biscarbonyl Re(I) complexes with electron-withdrawing groups in the diimine ligand, which could not be synthesized or were obtained only in low yields by the photochemical method. Me₃NO also selectively removed the carbonyl ligands in the trans position to the phosphorus ligands from the edge Re(I) complex units, which have the fac-[Re(N^N)(CO)₃(PR₂R')]⁺ structure, in linear-shaped Re(I) multinuclear complexes. This reaction was successfully applied to synthesize a novel precursor with ring-shaped multinuclear Re complexes (Re-rings) comprising different kinds of Re(I) units. The newly synthesized Re-rings, which consist of one Re unit with a 4,4'-bis(trifluoromethyl)-2,2'-bipyridine (CF₃bpy) ligand and one or two Re unit(s) with a 2,2'-bipyridine (bpy) ligand, showed almost quantitative excitation-energy harvesting ability from the Re unit(s) with bpy to that with CF₃bpy.

Phosphorescent platinum(ii) alkynyls end-capped with benzothiazole units

Phosphorescent platinum(ii) alkynyls. Phosphorescent trans-bis(alkynyl) bis(phosphine) or bis(cyanide) Pt^II derivatives (1–4) based on the 2-phenylbenzothiazole unit have been prepared. The negative solvatochromic behavior of 4 has been analyzed by the Kamlet–Taft solvent scale and the Gutmann's acceptor numbers. The optical properties were addressed by TD and DFT calculations on 2 and 4.

Copper-Based Coordination Polymer Nanostructure for Visible Light Photocatalysis

An air-stable copper-phenylacetylide nanobelt is synthesized and applied in organic pollutants elimination under visible light. Its versatile activity and reusability indicate it is a promising photocatalyst, arising from a band gap of 2.3 eV and the energetically favored electron transfer processes. The tunable structures and properties endow copper-based coordination polymers a prosperous prospect.

Synthesis and characterization of metallo-supramolecular polymers

The incorporation of metal centers into the backbone of polymers has led to the development of a broad range of organometallic and coordination compounds featuring properties that are relevant for potential applications in diverse areas of research, ranging from energy storage/conversion to bioactive or self-healing materials. In this review, the basic concepts and synthetic strategies leading to these types of materials as well as the scope of available characterization techniques will be summarized and discussed.

Our Expedition in Linear Neutral Platinum-Acetylide Complexes: The Preparation of Micro/nanostructure Materials, Complicated Topologies, and Dye-Sensitized Solar Cells

During the past few decades, the construction of various kinds of platinum-acetylide complexes has attracted considerable attention, because of their wide applications in photovoltaic cells, non-linear optics, and bio-imaging materials. Among these platinum-acetylide complexes, the linear neutral platinum-acetylide complexes, due to their attractive properties, such as well-defined linear geometry, synthetic accessibility, and intriguing photoproperties, have emerged as a rising star in this field. In this personal account, we will discuss how we entered the field of linear neutral platinum-acetylide chemistry and what we found in this field. The preparation of various types of linear neutral platinum-acetylide complexes and their applications in the areas of micro/nanostructure materials, complicated topologies, and dye-sensitized solar cells will be summarized in this account.

Molecular Architectonics of Naphthalenediimides for Efficient Structure-Property Correlation

We present a bioinspired design strategy to effectively tailor the assembly of naphthalenediimides (NDIs) into a wide variety of architectures by functionalizing with amino acid derivatives. This bioinspired process of custom designing and engineering molecular assemblies is termed "bioinspired architectonics". By employing minute structural mutations in the form of α-substituents of amino acids, we successfully engineered molecular assembly of NDIs into zero-dimensional (0D, spheres), one-dimensional (1D, fibers), and two-dimensional (2D, sheets) architectures. The 2D sheets of phenylalanine methylester appended NDI 1 showed remarkable bulk electron mobility of up to 1 cm(2) V(-1)s(-1). With the aid of photophysical, diffraction, and microscopy techniques we rationalize the effect of molecular structure with their ordering and electronic properties in an effort to find structure-property correlations via a bioinspired modular approach.

Synthesis of platinum-containing poly(phenyleneethynylene)s having various chromophores: aggregation and optical properties

Various platinum-containing phenylene–ethynylene–arylene polymers were synthesized, and the relationships between the optical properties and aggregation behaviour were examined.

Toward control of electron transfer in donor-acceptor molecules by bond-specific infrared excitation

Electron transfer (ET) from donor to acceptor is often mediated by nuclear-electronic (vibronic) interactions in molecular bridges. Using an ultrafast electronic-vibrational-vibrational pulse-sequence, we demonstrate how the outcome of light-induced ET can be radically altered by mode-specific infrared (IR) excitation of vibrations that are coupled to the ET pathway. Picosecond narrow-band IR excitation of high-frequency bridge vibrations in an electronically excited covalent trans-acetylide platinum(II) donor-bridge-acceptor system in solution alters both the dynamics and the yields of competing ET pathways, completely switching a charge separation pathway off. These results offer a step toward quantum control of chemical reactivity by IR excitation.

Dual ligand-based fluorescence and phosphorescence emission at room temperature from platinum thioxanthonyl complexes

Platinum complexes with σ-bonded thioxanthonyl (Tx) ligands exhibit, on irradiation into the Tx π→π* band, dual Tx-based fluorescence and phosphorescence emission with phosphorescence quantum yields of up to 19% in fluid solution at room temperature.

Ultrafast charge transfer dynamics in supramolecular Pt(ii) donor–bridge–acceptor assemblies: the effect of vibronic coupling

Thanks to major advances in laser technologies, recent investigations of the ultrafast coupling of nuclear and electronic degrees of freedom (vibronic coupling) have revealed that such coupling plays a crucial role in a wide range of photoinduced reactions in condensed phase supramolecular systems. This paper investigates several new donor–bridge–acceptor charge-transfer molecular assemblies built on a trans-Pt(ii) acetylide core. We also investigate how targeted vibrational excitation with low-energy IR light post electronic excitation can perturb vibronic coupling and affect the efficiency of electron transfer (ET) in solution phase. We compare and contrast properties of a range of donor–bridge–acceptor Pt(ii) trans-acetylide assemblies, where IR excitation of bridge vibrations during UV-initiated charge separation in some cases alters the yields of light-induced product states. We show that branching to multiple product states from a transition state with appropriate energetics is the most rigid condition for the type of vibronic control we demonstrate in our study.

The role of C-H and C-C stretching modes in the intrinsic non-radiative decay of triplet states in a Pt-containing conjugated phenylene ethynylene

The intrinsic non-radiative decay (internal conversion) from the triplet excited state in phosphorescent dyes can be described by a multi-phonon emission process. Since non-radiative decay of triplet excitons can be a significant process in organic light-emitting diodes, a detailed understanding of this decay mechanism is important if the overall device efficiency is to be controlled. We compare a deuterated Pt(II)-containing phenylene ethynylene with its non-deuterated counterpart in order to investigate which phonon modes control to the non-radiative decay path. We observe that deuteration does not decrease the non-radiative decay rate. A Franck-Condon analysis of the phosphorescence spectra shows that the electronic excitation is coupled strongly to the breathing mode of the phenyl ring and the C≡C carbon stretching modes, while high-energy C-H or C-D stretching modes play an insignificant role. We, therefore, associate the internal conversion process with the carbon-carbon stretching vibrations.