Assembling a Phthalocyanine and Perylenediimide Donor-Acceptor Hybrid through a Platinum(II) Diacetylide Linker

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).

Charge separation, recombination and intersystem crossing of directly connected perylenemonoimide-carbazole electron donor/acceptor dyads

Perylenemonoimide (PMI)-carbazole (Cz) compact electron donor/acceptor dyads were prepared to study the relationship between the mutual orientation of the electron donor/acceptor in the dyads and the spin-orbit charge transfer intersystem crossing (SOCT-ISC) efficiency. The PMI and the Cz units are connected via either a C-C or C-N bond, or with an intervening phenyl moiety. The photophysical properties of the dyads were studied with steady state and time-resolved optical spectroscopies. The fluorescence of the PMI unit in the dyads was generally quenched, due to photo-induced electron transfer, especially in polar solvents (the fluorescence has a biexponential decay in acetonitrile, τ_F = 1.4 ns/population ratio: 98.9%, and 9.6 ns/population ratio: 1.1%). The triplet state (lifetime τ_T = 14.7 μs) formation of the dyads is dependent on the solvent polarity, which is characteristic for SOCT-ISC. Femtosecond transient absorption spectra show that the charge separation takes 0.28 ps and the charge recombination takes 1.21 ns. Reversible photo-reduction of the PMI-Cz dyads and generation of the near IR-absorbing (centered at 604 nm and 774 nm) PMI radical anion (PMI^-˙) were observed in the presence of a sacrificial electron donor (triethylamine). These results are useful for study of the fundamental photochemistry of compact electron donor/acceptor dyads and for design of new heavy atom-free triplet photosensitizers.

Directly Linked Zinc Phthalocyanine-Perylenediimide Dyads and a Triad for Ultrafast Charge Separation

Directly linked to promote strong intramolecular interactions, donor-acceptor dyads and a donor-acceptor-donor triad featuring zinc phthalocyanine (ZnPc) as electron donor and perylenediimide (PDI) as electron acceptor have been synthesized and characterized. Owing to complementary absorption features of the entities, improved light absorption was witnessed in these conjugates. The optimized geometry and electronic structures showed the majority of the highest occupied molecular orbital (HOMO) on the ZnPc entity, whereas the lowest unoccupied molecular orbital (LUMO) was on the PDI entity, suggesting that the charge-separated states would be ZnPc⁺ -PDI^{. -} . The electrochemical and free-energy calculations suggested exothermic energy and/or electron transfer processes via the singlet states of PDI or ZnPc entities depending on the excitation wavelength of the laser used. The measured rates using femtosecond pump-probe spectroscopy coupled with global analysis of transient data revealed ultrafast energy transfer from ¹ PDI* to ZnPc followed by charge separation. However, when ZnPc was selectively excited, only electron transfer was witnessed wherein the time constants for forward and reverse electron transfer processes followed Marcus predictions. The absorption in a wide section of the solar spectrum and the ultrafast charge separation suggest the usefulness of these systems as good photosynthetic models.

A light harvesting perylene derivative - zinc phthalocyanine complex in water: spectroscopic and thermodynamic studies

A perylene derivative, namely N,N'-bis(2(trimethylammonium iodide)ethylene)perylene-3,4,9,10-tetracarboxyldiimide (TAIPDI) forms nanoscale columnar stacks in water that have been characterized by using optical absorption and emission measurements, dynamic light scattering (DLS), and transmission electron microscopy (TEM). This behaviour was compared with that of unstacked TAIPDI in methanol. Assembly formation between the one-dimensional TAIPDI stacks and zinc phthalocyanine tetrasulphonic groups (ZnPcS₄) via strong π-π and ionic interactions has been described in an aqueous medium. The formation constant of the supramolecular dyad has been determined as 2.94 × 10⁴ M^-1 from both the absorption and fluorescence measurements. Upon addition of ZnPcS₄, the fluorescence quenching of the singlet-excited state of TAIPDI was observed because of the electron transfer process from ZnPcS₄ to TAIPDI via the singlet-excited states of ZnPcS₄ and TAIPDI entities. The electrochemical studies supported the electron transfer pathways via the singlet states of ZnPcS₄ and TAIPDI. The thermodynamic parameters of the supramolecular complex have been determined from stopped-flow measurements. The interaction between ZnPcS₄ and TAIPDI occurs in two steps, where the rate constant of the second step with TAIPDI (207 ± 8 M^-1 s^-1) is much slower than the first one (3515 ± 101 M^-1 s^-1). Activation parameters for the complex formation (ΔH^# = 76 ± 11 kJ mol^-1 and ΔS^# = 83 ± 37 J K^-1 mol^-1, and ΔH^# = 221 ± 15 kJ mol^-1 and ΔS^# = 540 ± 50 J K^-1 mol^-1) were determined from variable temperature studies for the first and second steps, respectively. The significantly positive ΔS^# values found for both steps of the interaction reactions are consistent with a dissociative mechanism.

Incorporation of a platinum center in the pi-conjugated core of push-pull chromophores for nonlinear optics (NLO)

In this article, we describe the synthesis, redox characteristics, and linear and nonlinear optical (NLO) properties of seven new unsymmetrical push-pull diacetylide platinum-based complexes. These D-π-Pt-π-A complexes incorporate pyranylidene ligands as pro-aromatic donor groups (D), diazine rings as electron-withdrawing groups (A), and various aromatic fragments (styryl or thienylvinyl) as π-linkers separating the platinum diacetylide unit from the donor and the acceptor groups. This is one of the first examples of push-pull chromophores incorporating a platinum center in the π-conjugated core. The NLO properties of these complexes were compared with those of their purely organic analogues. All compounds (organic and organometallic) exhibited positive μβ values, which dramatically increased upon methylation of the pyrimidine fragment. However, this increase was even more significant in the complexes due to the presence of platinum in the π-conjugated core. The effects of the linker on the redox and spectroscopic properties of the complexes are also discussed. In addition, DFT calculations were performed in order to gain further insight into the intramolecular charge transfer (ICT) occurring through the platinum center.

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.

Submillisecond-lived photoinduced charge separation in a fully conjugated phthalocyanine–perylenebenzimidazole dyad

A fully electronically conjugated phthalocyanine–perylenemonoimidebenzimidazole system has been synthesized, in which the conjugation goes through the imide position of the perylene.