Conjugated Chromophore Arrays with Unusually Large Hole Polaron Delocalization Lengths

We report variable temperature X-band EPR spectroscopic data for the cation radical states of meso-to-meso ethyne-bridged (porphinato)zinc(II) (PZnn) oligomers. These [PZn2−PZn7]+ species span an average 18−75 Å length scale and display peak-to-peak EPR line widths (ΔBp-p) that diminish with conjugation length. Analysis of these EPR data show that PZnn+ structures possess the largest hole polaron delocalization lengths yet measured; experiments carried out over a 4−298 K temperature domain demonstrate remarkably that the charge delocalization length remains invariant with temperature. These cation radical EPR data are well described by a stochastic, near barrierless, one-dimensional charge hopping model developed by Norris for N equivalent sites on a polymer chain, where the theoretical EPR line width is given by ΔBp-p(N-mer) = (1/N1/2)ΔBp-p(monomer); PZnn+ oligomers are the first such systems to verify a Norris-type hole delocalization mechanism over a substantial (∼75 Å) length scale. Given the time scale of the EPR measurement, these data show that either (i) Franck−Condon effects are incapable of driving charge localization in [PZn2−PZn7]+, resulting in cation radical wave functions which are globally delocalized over a spatial domain that is large with respect to established benchmarks for hole-doped conjugated materials, or (ii) polaron hopping rates in these oligomers exceed 107 s-1, even at 4 K. Finally, this study demonstrates that polymeric building blocks having low magnitude inner sphere reorganization energies enable the development of electronic materials having long polaron delocalization lengths

Excitation of Highly Conjugated (Porphinato)palladium(II) and (Porphinato)platinum(II) Oligomers Produces Long-Lived, Triplet States at Unit Quantum Yield That Absorb Strongly over Broad Spectral Domains of the NIR

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 → T1 intersystem crossing dynamics (τisc: 5.2−49.4 ps). These species manifest high oscillator strength T1 → Tn transitions over broad NIR spectral windows. The facts that (i) the electronically excited triplet lifetimes of these PPdn and PPtn chromophores 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

Electron Spin Relaxation of Hole and Electron Polarons in π‑Conjugated Porphyrin Arrays: Spintronic Implications

Electron spin resonance (ESR) spectroscopic line shape analysis and continuous-wave (CW) progressive microwave power saturation experiments are used to probe the relaxation behavior and the relaxation times of charged excitations (hole and electron polarons) in <i>meso</i>-to-<i>meso</i> ethyne-bridged (porphinato)­zinc­(II) oligomers (<b>PZn</b>_{<b><i>n</i></b>} compounds), which can serve as models for the relevant states generated upon spin injection. The observed ESR line shapes for the <b>PZn</b>_{<b><i>n</i></b>} hole polaron (<b>[PZn</b>_{<b><i>n</i></b>}<b>]</b>^<b>+•</b>) and electron polaron (<b>[PZn</b>_{<b><i>n</i></b>}<b>]</b>^{<b>–•</b>}) states evolve from Gaussian to more Lorentzian as the oligomer length increases from 1.9 to 7.5 nm, with solution-phase <b>[PZn</b>_{<b><i>n</i></b>}<b>]</b>^<b>+•</b> and <b>[PZn</b>_{<b><i>n</i></b>}<b>]</b>^{<b>–•</b>} spin–spin (<i>T</i>₂) and spin–lattice (<i>T</i>₁) relaxation times at 298 K ranging, respectively, from 40 to 230 ns and 0.2 to 2.3 μs. Notably, these very long relaxation times are preserved in thick films of these species. Because the magnitudes of spin–spin and spin–lattice relaxation times are vital metrics for spin dephasing in quantum computing or for spin-polarized transport in magnetoresistive structures, these results, coupled with the established wire-like transport behavior across metal–dithiol-<b>PZn</b>_{<b><i>n</i></b>}–metal junctions, present <i>meso</i>-to-<i>meso</i> ethyne-bridged multiporphyrin systems as leading candidates for ambient-temperature organic spintronic applications

Modulation of Dark Conductivity over a 1 × 10⁻¹² to 1 × 10⁻⁵ S/cm Range Through Ancillary Group Modification in Amorphous Solids of Ethyne-Bridged (Porphinato)zinc(II) Oligomers

Modulation of Dark Conductivity over a 1 × 10−12 to 1 × 10−5 S/cm Range Through Ancillary Group Modification in Amorphous Solids of Ethyne-Bridged (Porphinato)zinc(II) Oligomer

Broad Spectral Domain Fluorescence Wavelength Modulation of Visible and Near-Infrared Emissive Polymersomes

Incorporation of an extended family of multi[(porphinato)zinc(II)] (PZn)-based supermolecular fluorophores into the lamellar membranes of polymersomes (50 nm to 50 μm diameter polymer vesicles) gives rise to electrooptically diverse nano-to-micron (meso) scale soft materials. Studies that examine homogeneous suspensions of 100 nm diameter emissive polymersomes demonstrate fluorescence energy modulation over a broad spectral domain of the visible and near-infrared (600−900 nm). These polymersomal structures highlight that the nature of intermembranous polymer-to-fluorophore contacts depends on the position and identity of the porphyrins' phenyl ring substituents. Emissive polymersomes are shown to possess reduced spectral heterogeneity with respect to the established optical signatures of these PZn-based supermolecular fluorophores in solution; additionally, selection of fluorophore ancillary substituents predictably controls the nature of polymer−emitter noncovalent interactions to provide an important additional mechanism to further modulate the fluorescence band maxima of these meso-scale emissive vesicles