Giorgio A. Pagani

Marked alkyl- vs alkenyl-substitutent effects on squaraine dye solid-state structure, carrier mobility, and bulk-heterojunction solar cell efficiency.

We report two new squaraine dyes substituted at the pyrrolic rings with n-hexyl (squaraine 1) or n-hexenyl (squaraine 2) chains. Although internal molecular structure variations are minimal, the presence of the terminal double bond results in a much more compact solid-state structure, dramatically affecting charge transport in the thin films; the hole mobility of 2 is approximately 5x that of 1, and the BHJ OPV power conversion efficiency (PCE) of 2 is approximately 2x that of 1. PCEs surpassing 2% for ambient solution-processed devices are demonstrated, the largest so far achieved for squaraine-based organic solar cells.

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.

Assessment of Water-Soluble π-Extended Squaraines as One- and Two-Photon Singlet Oxygen Photosensitizers: Design, Synthesis, and Characterization

Singlet oxygen sensitization by organic molecules is a topic of major interest in the development of both efficient photodynamic therapy (PDT) and aerobic oxidations under complete green chemistry conditions. We report on the design, synthesis, biology, and complete spectroscopic characterization (vis-NIR linear and two-photon absorption spectroscopy, singlet oxygen generation efficiencies for both one- and two-photon excitation, electrochemistry, intrinsic dark toxicity, cellular uptake, and subcellular localization) of three classes of innovative singlet oxygen sensitizers pertaining to the family of symmetric squaraine derivatives originating from pi-excessive heterocycles. The main advantage of pi-extended squaraine photosensitizers over the large number of other known photosensitizers is their exceedingly strong two-photon absorption enabling, together with sizable singlet oxygen sensitization capabilities, for their use at the clinical application relevant wavelength of 806 nm. We finally show encouraging results about the dark toxicity and cellular uptake capabilities of water-soluble squaraine photosensitizers, opening the way for clinical small animal PDT trials.

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.

Multichromophoric electrochromic polymers: Colour tuning of conjugated polymers through the side chain functionalization approach

Organic electrochromic materials have gained constantly increasing interest over the years with respect to their inorganic counterpart due to essentially two distinctive characteristics: their processability through solution based low cost processes and their wide colour palette. Such characteristic features enabled their application in displays, smart windows, electronic paper and ophthalmic lenses. Alongside the established concept of donor-acceptor polymers, side chain functionalized multichromophoric polymers are gaining attention as a highly performing and synthetically feasible alternative, particularly relevant to applications requiring a complete colourlessness in one of the accessible redox states of the material. The primary aim of the present article is to review all the results involving the tuning of the native electrochromic properties of simple conjugated polymers through the introduction of a discrete electrochromic molecule as a side chain substituent.

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%.

Electrochemical synthesis and characterization of polyconjugated polyfuran

Polyconjugated polyfuran (PF) was produced by electroreduction of 2,5-dibromofuran in acetonitrile using Ni(bipy)32+ as catalyst. Polymerization occurs only in the presence of excess Ni(bipy)32+ at potentials in the range −1.7 to −2.0 V versus Ag/Ag+ via binuclear organonickel complex. IR spectroscopy, elemental analysis and mass spectroscopy confirm that PF is constituted by 2,5-linked furan units and indicate a degree of polymerization > 100. Red PF films (λmax = 420 nm, Eg = 2.2 eV) are reversibly oxidized at 0.45 V and reduced at −2.5 V. Doping with AsF5 gives PF a conductivity of 10−3 S/cm. Polymers produced by anodic coupling of furan were also investigated for comparison. IR spectroscopy and elemental analysis indicate that they display a lower degree of conjugation due to the concomitant acidcatalyzed polymerization.

A squaraine–phthalocyanine ensemble: towards molecular panchromatic sensitizers in solar cells

A supramolecular phthalocyanine-squaraine ensemble which exhibits a large coverage of the solar spectrum from 850 to 250 nm has been prepared and characterized both photophysically and in bulk heterojunction solar cells.

Electrochemical preparation and electrochromic characteristics of dithienopyrrole-dithienothiophene, dithienopyrrole-thionaphtheneindole and dithienothiophene-thionaphtheneindole copolymers

Abstract Poly(dithienopyrrole-dithienothiophene) copolymers can be obtained as good conducting electrode films by electrolytic oxidation of acetonitrile solutions of monomer mixtures (electrolyte: tetrabutylammonium perchlorate). They show good electrochromic characteristics. Films of poly(dithienopyrrole-thionaphtheneindole) and poly(dithienothiophene-thionaphtheneindole) copolymers can be obtained in the same way as the previous ones. They are adherent to the electrodes but are insulating and non-electrochromic; the reason for this behaviour is proposed to be the break of conjugation in the polymeric chain due to the thionaphtheneindole moiety.