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Transient dynamical studies of bis[(5,5′-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)palladium(II)]ethyne (PPd2), 5,15-bis{[(5′-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)palladium(II)]ethynyl}(10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)palladium(II) (PPd3), bis[(5,5′-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)platinum(II)]ethyne (PPt2), and 5,15-bis{[(5′-10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)platinum(II)]ethynyl}(10,20-bis(2,6-bis(3,3-dimethylbutoxy)phenyl)porphinato)platinum(II) (PPt3) show that the electronically excited triplet states of these highly conjugated supermolecular chromophores can be produced at unit quantum yield via fast S1→ T1intersystem crossing dynamics (τisc: 5.2−49.4 ps). These species manifest high oscillator strength T1→ Tntransitions over broad NIR spectral windows. The facts that (i) the electronically excited triplet lifetimes of these PPdnand PPtnchromophores are long, ranging from 5 to 50 μs, and (ii) the ground and electronically excited absorptive manifolds of these multipigment ensembles can be extensively modulated over broad spectral domains indicate that these structures define a new precedent for conjugated materials featuring low-lying π−π* electronically excited states for NIR optical limiting and related long-wavelength nonlinear optical (NLO) applications. [ABSTRACT FROM AUTHOR]

We report a new method to generate families of organic fluorophores with any desirable emission wavelengths based upon the controlled oxidation of the light-emitting conjugated polymer, poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH−PPV), with meta-chloroperbenzoic acid (m-CPBA). In this method, m-CPBA reacts with ethylene moieties along the MEH−PPV backbone to create conjugation breaks, which gives rise to a gradual and controllable change in the emission wavelength. By simply adjusting the reaction time, light-emitting polymers possessing emission wavelengths spanning a 470−555 nm wavelength range can be easily prepared. Significantly, fluorescence quantum yields (QYs) of the oxidized polymers were comparable to or greater than that of the pristine polymer, contrary to the products typically resulting from oxidation of MEH-PPV by dioxygen. This new method should provide a simple way to generate color-tunable organic fluorophores with high QYs in a time- and cost-effective manner. [ABSTRACT FROM AUTHOR]

The electron transfer (ET) dynamics of an unusually rigid -stacked (porphinato)zinc(II)-spacer-quinone (PZn-Q) system, 5-8‘-(4‘ ‘-8‘ ‘‘-(2‘ ‘‘ ‘,5‘ ‘‘ ‘-benzoquinonyl)-1‘ ‘‘-naphthyl-1‘ ‘-phenyl)-1‘-naphthyl-10,20-diphenylporphinatozinc(II) (2a-Zn), in which sub-van der Waals interplanar distances separate juxtaposed porphyryl, aromatic bridge, and quinonyl components of this assembly, have been measured by ultrafast pump−probe transient absorption spectroscopy over a 80−320 K temperature range in 2-methyl tetrahydrofuran (2-MTHF) solvent. Analyses of the photoinduced charge-separation (CS) rate data are presented within the context of several different theoretical frameworks. Experiments show that at higher temperatures the initially prepared 2a-Znvibronically excited S1state relaxes on an ultrafast time scale, and ET is observed exclusively from the equilibrated lowest-energy S1state (CS1). As the temperature decreases, production of the photoinduced charge-separated state directly from the vibrationally unrelaxed S1state (CS2) becomes competitive with the vibrational relaxation time scale. At the lowest experimentally interrogated temperature (∼80 K), CS2defines the dominant ET pathway. ET from the vibrationally unrelaxed S1state is temperature-independent and manifests a subpicosecond time constant; in contrast, the CS1rate constant is temperature-dependent, exhibiting time constants ranging from 4 × 1010s-1to 4 × 1011s-1and is correlated strongly with the temperature-dependent solvent dielectric relaxation time scale over a significant temperature domain. Respective electronic coupling matrix elements for each of these photoinduced CS1and CS2pathways were determined to be ∼50 and ∼100 cm-1. This work not only documents a rare, if not unique, example of a system where temperature-dependent photoinduced charge-separation (CS) dynamics from vibrationally relaxed and unrelaxed S1states can be differentiated, but also demonstrates a temperature-dependent mechanistic transition of photoinduced CS from the nonadiabatic to the solvent-controlled adiabatic regime, followed by a second temperature-dependent mechanistic evolution where CS becomes decoupled from solvent dynamics and is determined by the extent to which the vibrationally unrelaxed S1state is populated. [ABSTRACT FROM AUTHOR]