Photoinduced electron transfer and nonlinear absorption in poly(carbazole-alt-2,7-fluorene)s bearing perylene diimides as pendant acceptors.

This paper reports the synthesis, photophysical behavior, and use in nanosecond optical-pulse suppression of a poly(2,7-carbazole-alt-2,7-fluorene) and a poly(3,6-carbazole-alt-2,7-fluorene) in which the carbazole N-positions are linked by an alkyl chain to one of the nitrogen atoms of a perylene-3,4,9,10-tetracarboxylic diimide (PDI) acceptor. It was found that the PDI pendants on the polymer side chain aggregated even in dilute solution, which extended the onset of PDI absorption into the near-infrared (NIR). Transient-absorption spectra of these polymers provide evidence for efficient electron transfer following either donor or acceptor photoexcitation to form long-lived charge-separated species, which exhibit strong absorption in the NIR. The spectral overlap between the transient species and the long-wavelength absorption edge of the aggregated PDI leads to reverse saturable absorption at 680 nm that can be used for optical-pulse suppression. Additionally, at high input energies, two-photon absorption mechanisms may also contribute to the suppression. PDI-grafted polymers exhibit enhanced optical-pulse suppression compared with blends of model materials composed of unfunctionalized poly(carbazole-alt-2,7-fluorene)s and PDI small molecules.

Synthesis and linear and nonlinear absorption properties of dendronised ruthenium(II) phthalocyanine and naphthalocyanine.

Ruthenium phthalocyanines and naphthalocyanines with axial dendronised pyridine ligands show high solubility in a variety of solvents, and exhibit solid-state absorption spectra that are comparable to those obtained in dilute solution, making them interesting candidates for optical limiting in the visible.

Conjugated polymer-fullerene blend with strong optical limiting in the near-infrared.

Optical-quality, melt processable thick films of a conjugated polymer blend containing poly(2-methoxy-5-(2-ethyl-hexyloxy)-(phenylene vinylene)) (MEH-PPV), a C(60) derivative (PCBM) and a plasticizer (1,2-di-iso-octylphthalate) have been developed and their nonlinear absorption and optical limiting properties have been investigated. These blend materials exhibited strong optical limiting characteristics in the near infrared region (750-900 nm), with broad temporal dynamic range spanning femtosecond to nanosecond pulse widths. The dispersion of the optical limiting figure-of-merit of the MEH-PPV:PCBM:DOP blend shows a peak near the wavelength of the MEH-PPV cation, indicating an important role of one-photon and two-photon induced charge transfer in the nonlinear absorption response.

Electron transfer-induced blinking in Ag nanodot fluorescence.

Various single-standed DNA-encapsulated Ag nanoclusters (nanodots) exhibit strong, discrete fluorescence with solvent polarity-dependent absorption and emission throughout the visible and near-IR. All species examined, regardless of their excitation and emission energies, show similar µs single-molecule blinking dynamics and near IR transient absorptions. The polarity dependence, µsec blinking, and indistinguishable µsec-decaying transient absorption spectra for multiple nanodots suggest a common charge transfer-based mechanism that gives rise to nanodot fluorescence intermittency. Photoinduced charge transfer that is common to all nanodot emitters is proposed to occur from the Ag cluster into the nearby DNA bases to yield a long-lived charge-separated trap state that results in blinking on the single molecule level.

Metalloporphyrin polymer with temporally agile, broadband nonlinear absorption for optical limiting in the near infrared.

A lead bis(ethynyl)porphyrin polymer possesses strong nonlinear absorption with unprecedented spectral/temporal coverage as a result of broad, overlapping two-photon and excited-state absorption bands with favorable excited-state dynamics. Consequently, this material exhibits effective optical limiting over a range of about 500 nm in the near infrared (ca. 1050 - 1600 nm) and for laser pulsewidths spanning from 75 fs to 40 ns. Introduction of the material in a waveguide device geometry results in a strong optical limiting response.

Zirconium phosphate/phosphonate multilayered films based on push-pull stilbazolium salt: synthesis, characterization and second harmonic generation.

The preparation of materials featuring enhanced second harmonic generation (SHG) values by self-assembly of molecules characterized by high second-order non-linear optic (NLO) activity is nowadays an important and challenging field of research. In order to show SHG the material must have an acentric structure with the dipoles of the molecular components oriented in the same direction and this is synthetically fairly difficult to achieve. This study describes the synthesis of the push-pull stilbazolium salt and its assembly in multilayered acentric thin films, on quartz glass surface, by using the zirconium phosphate/phosphonate (Zr-PO(x)) technique. A particular care has been paid to the optimization of the surface preparation and of the deposition conditions. This allows to obtain highly homogeneous lamellar inorganic-organic materials showing satisfactory second harmonic generation (SHG) values together with high chemical, thermal and mechanical stabilities which are necessary for their integration in optoelectronic devices.