Luminescent Pt(II) Complexes Using Unsymmetrical Bis(2-pyridylimino)isoindolate Analogues

A series of ligands based upon a 1,3-diimino-isoindoline framework have been synthesized and investigated as pincer-type (N∧N∧N) chelates for Pt(II). The synthetic route allows different combinations of heterocyclic moieties (including pyridyl, thiazole, and isoquinoline) to yield new unsymmetrical ligands. Pt(L1-6)Cl complexes were obtained and characterized using a range of spectroscopic and analytical techniques: 1H and 13C NMR, IR, UV-vis and luminescence spectroscopies, elemental analyses, high-resolution mass spectrometry, electrochemistry, and one example via X-ray crystallography which showed a distorted square planar environment at Pt(II). Cyclic voltammetry on the complexes showed one irreversible oxidation between +0.75 and +1 V (attributed to Pt2+/3+ couple) and a number of ligand-based reductions; in four complexes, two fully reversible reductions were noted between -1.4 and -1.9 V. Photophysical studies showed that Pt(L1-6)Cl absorbs efficiently in the visible region through a combination of ligand-based bands and metal-to-ligand charge-transfer features at 400-550 nm, with assignments supported by DFT calculations. Excitation at 500 nm led to luminescence (studied in both solutions and solid state) in all cases with different combinations of the heterocyclic donors providing tuning of the emission wavelength around 550-678 nm.

Spin-dependent electron transfer dynamics in a platinum-complex-donor-acceptor triad studied by transient-absorption detected magnetic field effect

For realization of efficient organic light-energy conversion systems, controlling the lifetime of photogenerated charge separated states in donor (D)-acceptor (A) molecules is of much importance; the spin dynamics is one of the important controlling factors. We previously reported that the covalently-linked 1,3-bis(2-pyridylimino)-isoindolate platinum (BPIPt)-dimethoxytriphenylamine (D)-naphthaldiimide (A) triad molecule (BPIPt-DA) exhibits a triplet-born long-lived charge separated state (BPIPt-D^•+A^•-), the lifetime of which is significantly increased from 4 µs to 10 µs by an applied magnetic field of 270 mT in room temperature tetrahydrofuran (THF). The purpose of the present study is to clarify detailed dynamics of spin-dependent generation and the decay of BPIPt-D⁺A^-. For this purpose, we measured transient optical absorption (TA) and the TA-detected magnetic field effect (MFE) as functions of temperature and dispersion media. In THF at 183 K, MFE-detected transient spectra of the intermediate BPIPt^•--D^•+A state are observed. We have successfully quantified the recombination loss at this state by a kinetic simulation of MFE without using any reference molecules. The lifetime of the final BPIPt-D^•+A^•- state in a cellulose acetate polymer matrix at room temperature is significantly prolonged to 20 µs at 0 mT and 96 µs at 250 mT compared to those in THF. From the comparison of temperature dependences of the two media, effects of molecular motions on the electronic coupling and the spin relaxation are discussed.

Magnetic Control of the Charge-Separated State Lifetime Realized by Covalent Attachment of a Platinum Complex

Dynamics of the photogenerated charge-separated (CS) state is studied for a newly synthesized molecular triad, in which the donor (D) dimethoxytriphenylamine, 1,3-bis(2-pyridylimino)isoindolate platinum (BPIPt), and the acceptor (A) naphthaldiimide are linked with a triethynylbenzene unit (BPIPt-DA). Photoexcitation of BPIPt gives rise to generation of a long-lived (∼4 μs) CS state BPIPt-D⁺A^-, of which the lifetime is considerably increased by an applied magnetic field of 270 mT. The positive magnetic field effect (MFE) is in contrast to the negative MFE for the reference DA molecule, which indicates successful switching of the initial spin state of the CS state from singlet to triplet. Simulations of the MFE and time-resolved electron paramagnetic resonance show that spin-selective charge recombination and spin relaxation are unaffected by attachment of BPIPt. The minimum impact of heavy atom substitution on the electronic and magnetic properties has been realized by the small electronic coupling mediated by the rigid meta-triethynylbenzene.

A series of pyridyl-amide-based ZnII/CdII coordination polymers and their polypyrrole-functionalized composite materials for tuning their photocatalytic properties

Six pyridyl-amide-based Zn^II/Cd^II coordination polymers have been solvothermally synthesized and decorated by polypyrrole for tuning their photocatalytic properties under visible irradiation.