Matteo Cozzuol

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.

Photo-induced charge transfer and nonlinear absorption in dyads composed of a two-photon-absorbing donor and a perylene diimide acceptor

This paper reports the synthesis and electrochemical and optical properties of two molecular dyads (Dyad 1 and Dyad 2) consisting of a 2,7-bis(4-(diarylamino)styryl)carbazole two-photon-absorbing donor chromophore, connected by different linkers to a perylene diimide (PDI) acceptor. The photo-induced charge transfer in these compounds is characterised using transient absorption measurements. The use of the compounds for optical limiting is discussed; because of spectral overlap between the donor two-photon absorption band and the one-photon absorption band of the PDI radical anion, the dyads exhibit enhanced nonlinear absorption at wavelengths between 700 and 800 nm relative to that seen for the two-photon absorbing donor chromophore. The stronger nonlinear absorption observed for Dyad 1vs.Dyad 2 is attributed to a higher yield of photo-generated radical ions and a longer lived charge-separated state, resulting from differences in the linker between the donor and acceptor.

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.

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.

Ultrafast exciton dynamics in donor-acceptor conjugated polymers

Aggregate-enabled ultrafast exciton dynamics in dithienopyrrole-benzothiadiazole based donor-acceptor conjugated polymers were investigated to address factors affecting the material performance in optoelectronic and photonic devices such as OPV, OLED, power limiters and polariton lasers.

Organic Materials for All-Optical Signal Processing and Optical Limiting

Third-order nonlinearities and optical switching and limiting figures of merit are reported for several conjugated organic materials. Polymethines with large real to imaginary hyperpolarizability ratios and conjugated polymers with strong nonlinear absorption will be discussed.

Large optical nonlinearities of conjugated porphyrin polymers in the Near Infrared

The optical nonlinearities of porphyrin polymers were investigated in the telecommunications band: large values, slow kinetics in solutions revealed efficient optical limiting while large values, fast kinetics in films suggested ultrafast applications should be possible.

Nonlinear optical properties of conjugated polymer charge transfer composites

Processing methods for optical-quality conjugated polymer charge-transfer composite films have been investigated. These materials exhibited strong energy-suppression characteristics in the near infrared regime for nanosecond pulses and show potential as efficient optical limiters for sensor protection.