Alessandro Abbotto

Di-branched di-anchoring organic dyes for dye-sensitized solar cells

The first examples of di-branched di-anchoring organic sensitizers were synthesized and used in dye-sensitized solar cells leading to red-shifted IPCE maxima and increased photocurrent when compared to the corresponding mono-branched mono-anchoring dye, yielding power conversion efficiency of 5.7% (4.9% with ionic liquid electrolyte) with enhanced stability under 1 sun conditions from the di-anchoring groups.

Novel heterocycle-based two-photon absorbing dyes.

[structure: see text]. The synthesis and nonlinear optical characterization of two novel heteroaromatic-based chromophores is described. The new dyes present an A-pi-D-pi-A general framework, where A is a pi-deficient heteroaromatic ring (pyridine, quinoline, benzothiazole) and D a pi-excessive pyrrolyl moiety. Both systems exhibit large two-photon absorption (TPA) values in the femtoseconds regime (TPA cross section as high as 150 x 10(-50) cm(4) s photon(-1) molecule(-1) with 150 fs laser pulses). Their TPA-based optical limiting activity is also shown.

Push–Pull Organic Chromophores for Frequency‐Upconverted Lasing

Properly designed organic molecules where a p-conjugated bridge is end-capped by an electron-donor and electron-withdrawing group (push‐pull chromophores) can show, under specific conditions, frequency-upconverted lasing emission. Materials based on these dyes are therefore able to convert the emission of a cheap and easily available infrared (IR) laser (e.g., 800 nm radiation) into more useful visible (vis) laser emission via a two-photon absorption induced fluorescence phenomenon. The design of the molecular structure, the substituent effect, and modulation of the electronic and geometric parameters can be used in order to optimize and tune frequency emission and conversion efficiency. Examples of some of the best dyes reported to-date and organic design strategies employed are discussed in this article.

Novel heteroaromatic-based multi-branched dyes with enhanced two-photon absorption activityElectronic supplementary information (ESI) available: Experimental section. See http://www.rsc.org/suppdata/cc/b3/b305995b/

The first examples of heterocycle-based multi-branched dyes with efficient two-photon absorption (TPA) activity are reported; the novel chromophores exhibit large TPA cross sections (as high as 1600 x 10(-50) cm4 s photon(-1) molecule(-1), measured with 150 fs laser pulses at 800 nm); a strong cooperative enhancement in the branched systems with respect to the one-dimensional sub-units is found.

Two-photon pumped frequency-upconversion lasing of a new blue-green dye material

Abstract The two-photon absorption and two-photon pumped (TPP) frequency-upconverted green lasing properties of a new dye, 1-(N-methyl-4-pyridinio)-2-(N-methylpyrrol-2-yl)ethene triflate (abbreviated as M-PPE) have been experimentally investigated. This new dye exhibits a low lasing threshold and high lasing efficiency when pumped with a 800-nm pulsed laser beam. The spectral, temporal, and spatial structures as well as the output/input characteristics of the TPP cavity lasing were measured using a 1 cm-path quartz cuvette filled with the M-PPE solution in dimethyl sulfoxide. The net conversion efficiency from the absorbed 800-nm pump pulse energy to the ∼ 543-nm upconverted cavity lasing energy was found to be as high as ∼ 11%.

Electron-rich heteroaromatic conjugated polypyridine ruthenium sensitizers for dye-sensitized solar cells

Ru(II) heteroleptic complexes as photosensitizers for dye-sensitized solar cells (DSCs) are presented. The article outlines design strategies, synthetic routes, optical and photovoltaic properties of ruthenium dyes based on polypyridines as ancillary ligands containing π-conjugated electron-rich heteroaromatic groups. The integration of donor heteroaromatic substituents, typically thiophene-based moieties, strongly improves the optical properties of the sensitizers in terms of bathochromic and hyperchromic shift compared to prototypical dyes N3 and N719. These favorable properties in turn yield DSCs with superior light harvesting abilities, higher external quantum efficiencies, improved device photocurrents, and top-ranked power conversion efficiencies. In combination with excellent stabilities under thermal stress and light soaking, this class of DSC photosensitizer has great potential for practical applications.

Panchromatic ruthenium sensitizer based on electron-rich heteroarylvinylene π-conjugated quaterpyridine for dye-sensitized solar cells

The first example of a heteroarylvinylene π-conjugated quaterpyridine Ru(II) sensitizer (N1044) was synthesized and used in dye-sensitized solar cells; the dye has an effective panchromatic absorption band, covering the entire visible spectrum up to the NIR region, and superior electrochemical characteristics (HOMO/LUMO and bandgap energies) with respect to previous representative Ru(II) bi- and quaterpyridine sensitizers. A record IPCE curve ranging from 360 to 920 nm has been measured with a maximum of 65% at 646 nm and still 33% efficiency at 800 nm; this leads to substantially increased photocurrent (19.2 mA cm(-2)) when compared to the prototype N719 Ru(II) sensitizer.

Tetraaryl ZnIIPorphyrinates Substituted at β-Pyrrolic Positions as Sensitizers in Dye-Sensitized Solar Cells: A Comparison withmeso-Disubstituted Push-Pull ZnIIPorphyrinates

A facile and fast approach, based on microwave-enhanced Sonogashira coupling, has been employed to obtain in good yields both mono- and, for the first time, disubstituted push-pull Zn(II) porphyrinates bearing a variety of ethynylphenyl moieties at the β-pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β-mono- or disubstituted Zn(II) porphyrinates and meso-disubstituted push-pull Zn(II) porphyrinates. We have obtained evidence that, although the HOMO-LUMO energy gap of the meso-substituted push-pull dyes is lower, so that charge transfer along the push-pull system therein is easier, the β-mono- or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β-monosubstituted porphyrinic dye interacting with a TiO2 surface and by the positive effect of the β substitution on the incident photon-to-current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350-650 nm). In contrast, meso-substitution produces IPCE spectra with two less intense and well-separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge-transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β-monosubstituted Zn(II) porphyrinates extremely promising sensitizers for use in DSSCs.

Thiocyanate-free cyclometalated ruthenium sensitizers for solar cells based on heteroaromatic-substituted 2-arylpyridines

The first examples of thiocyanate-free thiophene-substituted Ru(II) cyclometalated complexes, based on thiophene-derived 2-(2,4-difluorophenyl)pyridine ligands, are presented and investigated as photosensitizers in DSCs. Upon thiophene substitution the complexes presented enhanced optical properties compared to the reference dye with no thiophene substitution. DSCs based on the dithienyl-derived dye showed power conversion efficiencies up to 5.7%, more than twice that containing the complex without the thiophene substitution.

Effective two-photon absorption cross section of heteroaromatic quadrupolar dyes: dependence on measurement technique and laser pulse characteristics.

The linear and nonlinear optical properties of the heteroaromatic push-pull-push two-photon absorbing dye N-methyl-2,5-bis[1-(N-methylpyrid-4-yl)ethen-2-yl]-pyrrole ditriflate (PEPEP) are reported. The determination of the two-photon absorption (TPA) cross-section spectrum has been performed with different techniques: femtosecond TPA-white light continuum probe experiments, two-photon-induced fluorescence, and open aperture Z-scan measurements using both nanosecond and femtosecond laser pulses. The measured TPA cross sections and their wavelength dispersion show a marked dependence on the parameters of the laser pulses and on the measurement technique employed. These properties are discussed in terms of the different microscopic mechanisms that can contribute to the multiphoton absorption processes, with different weight depending on the measurement conditions and on the photophysical parameters of the dye.