A family of π-extended platinum(II) porphyrins has been synthesized and incorporated into solution processed polymer light emitting diodes (PLEDs) and vapor deposited multilayer organic light emitting diodes (OLEDs), giving rise to devices with peak emission ranging from 771 to 1005 nm. The longest wavelength emitter, platinum(II)-5,10,15,20-(3,5di-tert-butylphenyl)tetraanthroporphyrin (Pt-Ar 4 TAP), shows an emission maximum at 1005 nm, an external quantum efficiency (EQE) of 0.12%, and a maximum radiant emittance (R max ) of 0.23 mW/cm 2 in single layer PLED architectures, which is enhanced to an EQE of 0.20% with an R max of 0.57 mW/cm 2 upon vapor deposition of an electron transport layer. In an effort to understand substituent effects and enhance the performance of π-extended Pt-porphyrins in PLEDs and OLEDs, a family of Pt-tetrabenzoporphyrins (Pt-TBPs) with varying functionality was investigated. The luminescent lifetimes of the Pt-TBPs in solution and in films were measured, and a strong correlation was demonstrated between the film lifetimes and the PLED and OLED efficiencies. An improvement in external quantum efficiency (EQE) from 2.07 to 2.49% for PLEDs and from 8.0 to 9.2% for OLEDs was observed between the less substituted Pt-tetraphenyltetrabenzoporphyrin and the more substituted 10,15,tetrabenzoporphyrin. The PLED EQEs were further enhanced to 3.02% with the disubstituted Pt-5,15-(3,5-di-tert-butylphenyl)tetrabenzoporphyrin; however, this increase was not observed for the OLEDs where an EQE of 7.8% was measured.

A comprehensive photophysical study is reported on a family of π-extended platinum(II) porphyrin complexes. The platinum(II) complexes are synthesized from the corresponding free base porphyrins by treatment with platinum(II) acetate in hot benzonitrile, affording the complexes in considerably higher yield than by reaction with platinum(II) chloride. A quantitative study of the absorption and luminescence properties of the metalloporphyrins is presented. A series including tetraarylbenzo-, tetraarylnaphtho-, and tetraarylanthroporphyrin exhibits efficient phosphorescence at 773, 890, and 1020 nm in the near-infrared region, with quantum yields of 0.35, 0.15, and 0.08, respectively. The triplet lifetimes and phosphorescence yields decrease with increasing emission wavelength, consistent with energy gap law behavior. A set of six Pt-tetrabenzoporphyrins (TBPs) with different meso-substituents were examined. The Pt-TBPs exhibit efficient phosphorescence with λ max ∼ 770 nm and with a quantum yield ranging from 0.26−0.49, depending on the substitution pattern. The results show that the 5,15-diarylbenzoporphyrins feature 50−60% higher phosphorescence emission yield compared to the 5,10,15,20-tetraarylbenzoporphyrins. The highest phosphorescence quantum efficiency is observed for a platinum(II) 5,15-diarylbenzoporphyin which emits at 770 nm with a quantum yield of 49%.

Chromophores and materials that exhibit nonlinear absorption over a broad spectrum and with high temporal dynamic range are of interest for application in materials engineering and biology. Recent work by a number of research groups has led to the development of a new family of organometallic chromophores and materials featuring interesting and useful nonlinear absorption properties. These systems contain the platinum acetylide moiety as a fundamental molecular unit, combined with delocalized, π-conjugated electron systems. These organometallic chromophores provide a unique combination of properties, such as negligible ground state absorption in the visible region, large spin-orbit coupling giving rise to high triplet excited state yield, triplet lifetime in the microsecond domain, high two-photon cross-section in the visible and near-infrared regions, and high triplet-triplet absorption cross-section in the visible and near-infrared region. This Spotlight on Application highlights recent developments in this area, combining background and review on nonlinear absorption in platinum acetylide chromophores and describing significant recent results from our own laboratory.

A series of platinum-containing organometallic dimer complexes has been synthesized and the photophysical properties have been investigated under one- and two-photon (2PA) absorption conditions. The complexes have the general structure [DPAF-C[triple bond]C-Pt(PBu(3))(2)-C[triple bond]C-Ar-C[triple bond]C-Pt(PBu(3))(2)-C[triple bond]C-DPAF], where Ar is a pi-conjugated unit, Bu = n-butyl, and DPAF = diphenylamino-2,7-fluorenylene. The core Ar units include 1,4-phenylene, 2,5-thienylene, 5,5'-(2,2'-bithienylene), 2,5-(3,4-ethylenedioxythiophene, 2,1,3-benzothiadiazole, and 4,7-dithien-2-yl-2,1,3-benzothiadiazole. Absorption and photoluminescence spectroscopy indicates that the complexes feature low-lying excited states based on both the core [-Pt(PBu(3))(2)-C[triple bond]C-Ar-C[triple bond]C-Pt(PBu(3))(2)-] chromophore as well as the DPAF units. Photoexcitation of the complexes produces a singlet state excited state, which rapidly undergoes intersystem crossing to afford a triplet state that has a lifetime in the microsecond time domain. In most cases, the lowest energy triplet state is localized on the core chromophore. Femtosecond 2PA spectra are measured along with triplet-triplet absorption spectra and nanosecond intensity-dependent transmission for solutions of the complexes. Each of the complexes features a 2PA absorption band in the near-infrared region (lambda approximately 700-750 nm) with a cross section 50-200 GM that is ascribed to the DPAF chromophore. The complexes also feature broad triplet-triplet absorption throughout the visible and near-infrared regions (lambda approximately 500-800 nm, (TT) approximately 5-10 x 10(4) M(-1) cm(-1)). Each of the complexes exhibits efficient nonlinear absorption of nanosecond pulses in the near-infrared region (600-800 nm), and we demonstrate that effect is most efficient in the chromophores where the 2PA cross section maxima coincides spectrally with the excited triplet state absorption.

This perspective seeks to identify an area of soft materials research focused on the study of functional polyelectrolytes. These materials combine the useful properties intrinsic to polyelectrolyte chains, with added functionality provided by specific molecular (or polymeric) functional groups that are present in the polymer backbone or as a pendant functionality. Examples are provided to demonstrate how the combined functionality can be used to create films and assemblies with interesting and useful optical, electro-optical, and electronic properties.

A series of poly(arylene ethynylene) conjugated polyelectrolytes (CPEs) substituted with carboxylic acid side groups have been synthesized and characterized. The polymers feature a backbone consisting of a carboxylated dialkoxyphenylene-1,4-ethynylene unit alternating with a second arylene ethynylene moiety of variable electron demand. The HOMO-LUMO gap is varied across the series, giving rise to a set of four polymers that have absorption maxima ranging from 404 to 495 nm. The CPEs adsorb effectively from solution onto nanostructured TiO(2) films, giving rise to TiO(2)/CPE films that absorb approximately 90% of the incident light at the absorption band maximum. The photocurrent generation efficiency of the TiO(2)/CPE films was examined in a solar cell configuration using an I(3)(-)/I(-) propylene carbonate electrolyte and a Pt/fluorine-doped tin oxide counter electrode. Most of the films exhibit good photocurrent generation efficiency with a peak quantum efficiency of approximately 50% at wavelengths corresponding to the polymers' absorption band maximum. Interestingly, the photocurrent generation efficiency for the lowest-band-gap polymer is substantially lower compared to the other three systems. This effect is attributed to efficient nonradiative decay of excitons at trap sites arising from interchain contacts distal from the TiO(2)/CPE interface.

We report three platinum acetylide acrylate monomers containing known two-photon absorption (TPA) chromophores and their covalent incorporation into polymers via free radical polymerization with methyl methacrylate. The photophysical properties of the platinum acetylide monomers and resulting poly(methyl methacrylate) (PMMA) copolymers were investigated to determine if the one- and two-photon photophysical properties of the chromophores were maintained in the copolymers. The photophysical properties of the series of copolymers were studied in solution and solid state with minimum shifts exhibited in the ground state absorption, photoluminescence, and triplet-triplet transient absorption spectra. The polymer films displayed markedly stronger phosphorescence and longer triplet excited state lifetimes than the polymers in solution or the monomers. The incorporation of the platinum acetylide chromophores into the PMMA copolymers allows the materials to be cast as thin films or into free-standing monoliths. Films with ~3.6 μm in thickness and monoliths with 1 mm path length were fabricated and examined. The nonlinear absorption responses of the polymers in solution were measured via the nanosecond z-scan method, and the solid state polymer monoliths were measured via nonlinear transmittance. Both measurements indicate that the polymers exhibited strong transmittance attenuation at input pulse energies exceeding 100 μJ.

A series of cis-platinum(II) acetylide complexes containing two-photon-absorbing chromophores have been synthesized and characterized to explore the effects of stereochemistry on the nonlinear absorption properties. The molecules feature 4-(phenylethynyl)phenylethynylene (PE2), diphenylaminofluorene (DPAF), and benzothiazolylfluorene (BTF) ligands. The photophysical properties were investigated under one-and two-photon conditions and compared to the known trans analogues via UV−visible absorption, photoluminescence, femtosecond and nanosecond transient absorption (TA), nanosecond z-scan, and femtosecond two-photon absorption (2PA). The bent cis complexes exhibit blue shifts in the absorption, emission, femtosecond, and nanosecond TA spectra along with lower molar extinction coefficients and lower phosphorescence yields relative to the trans complexes suggesting less efficient Pt-induced spin−orbit coupling and intersystem crossing in the cis configuration. The cis chromophores are noncentrosymmetric and therefore show dipolar behavior with a pronounced 2PA in the 0−0 transition of the S 0 → S 1 band, while the trans complexes show quadrupolar behavior with a forbidden 0−0 transition. In the S 0 → S n region, both cis and trans complexes show intense two-photon-absorption bands (up to 3700 GM by the peak cross section for cis-BTF) which contain a significant contribution from the excited state absorption (S 1 → S n ). All six complexes exhibit comparable nonlinear absorption response with a significant contribution from triplet−triplet absorption that slightly favors trans complexes but is more strongly dependent upon the structure of the π-conjugated chromophore.