KEYWORDS: Absorption, Ruthenium, Dye sensitized solar cells, Photovoltaics, Solar energy, Solar cells, Nanoparticles, Quantum efficiency, Energy efficiency, Titanium dioxide
A new ruthenium sensitizer based on a heteroaromatic-4,4'-π-conjugated 2,2'-bipyridine, bearing conjugated π-excessive
heteroaromatic rings as donors is presented. Dye-sensitized solar cells have been fabricated based on the novel ruthenium
complex [Ru(II)LL'(NCS)2] (L = 4,4'-bis[(E)-2-(3,4-ethylenedioxythien-2-yl)vinyl]-2,2'-bipyridine, L' = 4,4'-
(dicarboxylic acid)-2,2'-bipyridine) and their photoelectrochemical properties have been measured under various
conditions. Using this sensitizer photovoltaic efficiencies up to 9.1 % under standard global AM 1.5 sunlight were
obtained. DFT/TDDFT calculations have been performed for the sensitizer in solution. By calculating the excited states
energy and character and comparing the results with the conduction band edge of a model TiO2 nanoparticle, we were
able to highlight the factors affecting the measured photovoltaic efficiencies.
We present the design, synthesis, and characterization of a class of heteroaromatic bichromophores in order to investigate intermolecular interactions and their effect on optical and nonlinear optical properties. As a design strategy we have linked two dipolar or quadrupolar units through a non-conjugated alkyl chain. The two units are connected either through their donor or their acceptor end-groups. This study represents a first step towards the design of bi- and multichromophoric systems with optimized NLO responses in order to exploit collective and cooperative effects from interchromophore interactions.
Artificial opals are a simple and cheap playground to manipulate the propagation of light. The interest in these kind of
photonic crystals is further increased by the possibility to be infiltrated with highly polarisable media like organic
semiconductors, i.e. conjugated polymers, push-pull molecules and multipolar chromophores.
In this work, we report on the optical properties of polystyrene opals infiltrated with a heteroaromatic quadrupolar
derivative endowed with strong nonlinear optical properties (two-photon absorption) in solution. The insertion of
tris(ethylene glycol)monomethyl ether chains on the conjugated skeleton allows the molecule to be soluble in water, a
non-solvent for polystyrene. This condition is fundamental in order to attempt opal infiltration.
Variable angle transmittance and photoluminescence spectroscopy are used to characterize the system. The bathochromic
shift of the opal stop band upon immersion in the chromophore solution confirms that the infiltration process easily takes
place preserving a dielectric contrast suitable for further investigations.
Photoluminescence spectra recorded at different emission angle with respect to the normal of the sample for both the
chromophore solution and opals infiltrated with such solution show interesting characteristics. The presence of opal
modifies the chromophore emission spectrum by filtering the light for wavelengths corresponding to those of the stop
band and according to its dispersion.
The synthesis and characterization of novel heteroaromatic-based two-photon absorption (TPA) dyes for bio-conjugation is described; the new isothiocyanate and maleimide derive from a class of novel efficient quadrupolar and octupolar/branched chromophores relying on the electronic effects of electron-poor and electron-rich simple heteroaromatic rings; the new systems exhibit very large TPA cross-sections, high chemical stability, and very low photobleaching.
The one photon and two photon excitation spectral properties (absorption, emission spectra, singlet lifetime) of a very efficient two photon absorber, dimethyl-pepep, have been measured in solution. The one photon excitation peak lye near 525 nm and the emission falls at 600 nm, where autofluorescence of cells is weak. The value of the singlet-triplet conversion rate, obtained by two-photon excitation fluorescence correlation spectroscopy, has a quadratic dependence on the excitation power and is comparable to that shown by the dye rhodamine. Preliminary results on stained cells from yeast Saccaromices cerevisiae and Paramecium primaurelia show that the dye preferentially stains DNA in the cell. A direct comparison with a DNA stainer, Dapi, is also performed. Some measurements of the dye functionalized to react with lysine and n-terminal residues of protein are presented. Moreover, this dye can be employed in order to follow in detail some cellular processes such as nuclei division. In vitro fluorescence titration of dimethyl-pepep with calf thymus DNA allowed to estimate the values of the dye-DNA association constant versus ionic strength, and an affinity close to that of ethidium bromide is found.
A novel scheme for implementing the joint exploitation of different, somehow complementary mechanisms of nonlinear transmission in an optical limiting device is proposed. As active materials we have chosen the fullerene derivative FULP, as a reverse saturable absorber, and a new heterocyclic quadrupolar dye, PEPEP, with highly efficient multiphoton absorption for nanosecond pulses. The nonlinear absorption properties of PEPEP in solution are extensively investigated for both femtosecond and nanosecond pulses. When Z-scan experiments are performed with nanosecond pulses, much larger effective cross sections are measured than with femtosecond pulses and with remarkably different wavelength dispersion. This is interpreted as due to two-photon absorption followed by one-photon absorption from the excited state. Chemically modified nonlinear molecules are incorporated in a hybrid organic-inorganic sol-gel matrix. Sufficiently high concentrations are achieved to allow the assembling of thin sol-gel disks into a "tandem" limiter with a total thickness smaller than the Rayleigh range of the focused laser beam. Preliminary testing of our limiter is reported and shows encouraging results. The resistance of the FULP-doped sol-gel glass to laser damage is substantially improved and the nonlinear attenuation at high pulse energies is enhanced.
We report the synthesis of sol-gel materials based on highly efficient heterocycle-based push-pull chromophores showing second- and third-order nonlinear optical activity. We show the proper functionalization of the best performing chromophores and their incorporation into a hybrid organic- inorganic sol-gel matrix. Different types of functionalization of the active molecule have been considered, including hydroxyl and alkoxysilyl end-groups. The functionalization strategy responded to different criteria such as stability and synthetic availability of the final molecular precursors, their solubility, and the used synthetic approach to the sol-gel material. The synthesis of the sol-gel materials has been tuned in order to preserve molecular properties and control important factors such as final concentration of the active dye in the matrix. Both acid- and base-catalyzed sol-gel synthesis has been taken into account. 3-Glycidoxypropyltrimethoxysilane and 3- aminopropyltriethoxysilane have been used as the organically modified alkoxides to prepare the hybrid organic-inorganic matrix. Characterization of the spectroscopic properties of the sol-gel materials is presented.
We report here on the synthesis of new polymers carrying chromophores active for second- and third-order nonlinear optical (NLO) applications. Some of these systems show exceptionally large NLO molecular properties such as high first hyperpolarizabilities and high two-photon-pumped frequency-upconversion lasing efficiencies. Different types of polymeric and copolymeric backbones have been investigated in order to tune the properties of the bulk material and optimize its efficiency. Factors such as the linking reaction approach, chromophore number density, cross-linking ratio, and thermal properties can be controlled and tuned depending on the application. In particular, we have found that NLO molecular components carrying a primary amino group attached to the chromophore by means of a short aliphatic chain can act as comonomers in poly(amino-amine) synthesis, a family of synthetic polymers in which amido and tertiary amino groups are regularly arranged along the main backbone. Linear and soluble, or, alternatively highly crosslinked poly(amido-amine) networks can be easily obtained with high loading of the chromophore. In addition, hydroxylated chromophores can be covalently linked to properly functionalized acrylic polymers, such as poly(2-methacryloxyethyl)imidazolylformate.
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