Two‐photon excitation and optical limiting in polyfluorene derivatives

Abstract

Fluorene-based polymers are widely known materials due to a combination of features such as photoluminescence and electroluminescence, oxidative stability, and filmforming ability. However, studies reporting nonlinear optical properties in this class of conjugated polymer are scarce. Here, we report a new class of polyfluorene derivatives poly(9,9 0 -n-dihexyl-2,7-fluorenedilvinylene-alt-1,4-phenylenevinylene), poly(9,9 0 -n-dihexyl-2,7-fluorenedilvinylene-alt-2,5-thiophene), and poly[(9,9-di-hexylfluorenediylvinylene-alt-1,4phenylenevinylene)-co-((9,9 0 -(3-t-butylpropanoate) fluorene-1,4-phenylene)] displaying high two-photon absorption (2PA) in the spectral range from a 490 to 1100 nm. The 2PA cross-section peak values for these materials are as high as 3000 Gö ppert Mayer (1 GM ¼ 1 Â 10 À50 cm 4 s/photon), which is related to the high degree of conjugation along the polymer backbone. The polymers that were used in this study presented a strong two-photon luminescence and also displayed optical limiting behavior, which, in combination with their well-established properties, make them highly suitable for nonlinear optical devices.

Femtosecond Two-Photon Absorption Spectroscopy of Poly(fluorene) Derivatives Containing Benzoselenadiazole and Benzothiadiazole

“…As can be seen in Figure 2 , the 2PA spectra present an intense 2PA band at 360 nm (720 nm for the 2PA transition) attributed to the strongly 2PA-allowed 1Ag-like → mAg-like transition [ 28 ]. Such transition is characteristic of poly(fluorene) derivatives and can reach thousands of GM [ 13 , 28 , 29 ]. The maximum 2PA cross section obtained for this transition was 530 GM (PFeBSe) and 620 GM (PFeBT).…”

“…At the same time, semiconductor polymers are fascinating materials for studying nonlinear optical effects such as two-photon absorption (2PA). Organic materials for 2PA are interesting for applications in 3D micro-fabrication and micromachining [ 7 , 8 , 9 , 10 ], 3D data storage [ 11 , 12 ], optical power limiting [ 13 , 14 ], two-photon induced photopolymerization [ 15 ], two-photon pumped laser [ 16 ], and so on. The key feature for such applications is the quadratic dependence of the 2PA process on the excitation irradiance, which provides spatial confinement of excitation [ 17 ].…”

Kinetics of light induced defect creation in organic solar cells

“…The 2-3 eV energy of yellow or white light is considerably smaller than the C-H bond strength raising a question about the bond-breaking mechanism. The bond could be broken by 2-photon excitation but the two-photon cross-section is much too low, 13 and the expected dependence on the square of the intensity is not observed. A two-step process in which a photon excites a previously excited electron or hole is another possibility.…”

Synthesis of a PPV‐fluorene derivative: Applications in luminescent devices

“…and after purification it was reacted via Wittig reaction with 1,4‐bromobenzaldehyde giving the monomer II , which exhibited a yellow color and a strong blue emission. The detailed procedures for the preparation monomer II and LaPPS42, through the Suzuki route are described in the literature . The number‐average and the weight‐average molecular weights (Mn and Mw) of the copolymer were determined by SEC, resulting in 31,300 and 96,000 g mol −1 , respectively.…”