Teruo Shinmyozu

Excimer–Monomer Photoluminescence Mechanochromism and Vapochromism of Pentiptycene-Containing Cyclometalated Platinum(II) Complexes

The ability of the bulky H-shaped pentiptycene scaffold in promoting the mechanochromic and vapochromic luminescence properties for organometallic materials has been demonstrated with the N^C^N cyclometalated platinum(II) complexes [X-NCNPtY], where X = Br or Pa, the substituent on the terdentate dipyridylbenzene N^C^N ligand, and Y = Cl or Pa, the ancillary ligand, in which Pa = pentiptycene acetylene. Intermolecular interactions between the planar NCNPt cores are described by π-π and d-π interactions with negligible PtII···PtII bonding, corresponding to ligand-centered excimer rather than metal-metal-to-ligand charge-transfer emission, for these platinum(II) complexes in aggregates and in the solid state. Interplay of the relative excimer-to-monomer emission intensity in response to external force and/or vapor stimuli accounts for the luminescence mechanochromism and vapochromism of the pentiptycene-incorporated platinum(II) complexes [Pa-NCNPtCl], [Br-NCNPtPa], and [Pa-NCNPtPa], whereas the pentiptycene-free counterpart [Br-NCNPtCl] undergoes little or no emission color response. In particular, the complex [Pa-NCNPtCl] displays a distinct response to aromatic versus nonaromatic organic vapors: namely, aromatic vapors such as benzene convert the excimer emission to monomer emission, but the opposite is true with nonaromatic vapors. A two-stage emission color change from red to orange and then to yellow could thus be achieved by grinding and by subsequent benzene-vapor fuming. Another feature associated with [Pa-NCNPtCl] is an aggregation-induced green → magenta luminescence color change in water/tetrahydrofuran mixed solutions. The structure-luminescence property relationship is discussed in relation to intermolecular interactions and packing modes that depend on the number and positions of pentiptycene groups.

Multistep Electron Transfer Systems Containing [2.2]- or [3.3]Paracyclophane

Paracyclophanes (PCPs), which exhibit interesting properties due to their transannular interactions, have been employed as a spacer in various electron transfer (ET) systems. In the present work, we investigated ET processes in dyads and triads containing [2.2]PCP or [3.3]PCP as donors to study their properties in multistep ET processes. The dyad molecules of PCP and 1,8-naphthalimide (NI) as a photosensitizing electron acceptor exhibited charge separation (CS) upon excitation of NI. In addition, triads of NI, PCP, and carbazole showed charge shift after an initial CS, thus confirming multistep ET. In this study, we demonstrated that use of [3.3]PCP in place of [2.2]PCP enhanced the initial CS rate. Lower oxidation potentials and a smaller reorganization energy for [3.3]PCP are shown to be key factors for this enhanced CS rate. Both of these properties are closely related to the strained structure of PCP; hence, the present results demonstrate the importance of strain in ET chemistry.

Synthesis, Optical Properties, and Electronic Structures of Tetrakis(pentafluorophenyl)tetrathiaisophlorin Dioxide

The synthesis, structure, optical and redox properties, and electronic structure of tetrakis(pentafluorophenyl)tetrathiaisophlorin dioxide (12) are reported. Oxidation of tetrakis(pentafluorophenyl)tetrathiaisophlorin (11) with dimethyldioxirane afforded the oxidized product, which was the tetrathiaisophlorin with two thiophene 1-oxide moieties (12). More significant nonplanarity and greater bond length alternation in 12 than those of 11 were observed by X-ray structural analysis. The absorption spectrum of 12 contains two bands at λ=348 and 276u2005nm, with a weak tail that extends to λ≈650u2005nm. Analysis of the magnetic circular dichroism spectrum of 12, based on Michls 4N-perimeter model and molecular orbital calculations, indicate that the broad band at λ=348u2005nm appears to contain N2 and P2 bands, and 12 is classified as a 4nπ system, similar to 11. The nuclear-independent chemical shift values and (1) Hu2005NMR spectroscopy data indicate that 12 has more antiaromatic character than 11.

Donor-Donor'-Acceptor Triads Based on [3.3]Paracyclophane with a 1,4-Dithiafulvene Donor and a Cyanomethylene Acceptor: Synthesis, Structure, and Electrochemical and Photophysical Properties

Donor-donor-acceptor triads (1, 2), based on [3.3]paracyclophane ([3.3]PCP) as a bridge, with electron-donating properties (D) using 1,4-dithiafulvene (DTF; TTF half unit) as a donor and dicyanomethylene (DCM; TCNE half unit) or an ethoxycarbonyl-cyanomethylene (ECM) as an acceptor were designed and synthesized. The pulse radiolysis study of 1u2009a in 1,2-dichloroethane allowed the clear assignment of the absorption bands of the DTF radical cation (1u2009a.+ ), whereas the absorption bands due to the DCM radical anion could not be observed by γ-ray radiolysis in 2-methyltetrahydrofuran rigid glass at 77u2005K. Electrochemical oxidation of 1u2009a first generates the DTF radical cation (1u2009a.+ ), the absorption bands of which are in agreement with those observed by a pulse radiolysis study, followed by dication (1u2009a2+ ). The ESR spectrum of 1u2009a.+ showed a symmetrical signal with fine structure and an ESR simulation predicted that the spin of 1u2009a.+ is delocalized over S and C atoms of the DTF moiety and the central C atom of the trimethylene bridge bearing the DTF moiety. Pulse radiolysis, ESR, and electrochemical studies indicate that the DTF radical cation of 1u2009a.+ is more stable than that of 6.+ , and the latter shows a strong tendency to dimerize. This result indicates that the [3.3]PCP moiety as a bridge can stabilize the DTF radical cation more than the 1,3-diphenylpropane moiety because of kinetic stability due to its rigid structure and the weak electronic interaction of DTF and DCM moieties through [3.3]PCP.