Three‐ and Four‐Photon Excitation of Poly(2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene) (MEH‐PPV)

Abstract

In the presence of intense laser pulses, molecules can instantaneously absorb two or more photons, being promoted to an excited state. These multiphoton absorption processes exhibit transition probabilities proportional to I n , where I is the intensity of the laser pulse and n is the number of photons, which implies in-chromophore excitation with a high degree of spatial selectivity. In addition, the ability to create excited states with less-energetic photons provides improved penetration in absorbing or scattering materials. These features indicate the suitability of multiphoton absorption for a variety of applications, such as three-dimensional (3D) optical data storage, [1] optical limiting, [2,3] lithographic microfabrication, [4] fluorescence excitation microscopy and imaging, [5,6] photodynamic therapy, [7] and infrared frequency-up-conversion lasing.[8]To exploit fully the potential of multiphoton-absorbing materials, molecules presenting high multiphoton cross sections are required. In this direction, several molecular architectures, based in strategies employing conjugated systems, have been proposed in order to develop molecules with large nonlinear absorptivity.[5] Hence, conjugated polymers seem to be good candidates for photonic applications since they combine interesting optical and electrical properties with potentially high nonlinearities. The application of poly(p-phenylenevinylene) (PPV)-based conjugated polymers in the emerging technologies of organic electro-and photoluminescence has generated immense interest. [9,10] Although strong two-photon absorption has been shown in PPV derivatives, [11,12] its multiphoton absorption processes have still not been thoroughly explored from either a fundamental or applied point of view. In this Communication we report three-and four-photon absorption (3PA and 4PA) cross-section spectra for poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) chloroform solution, which exhibits values comparable to other materials reported in the literature. A resonant enhancement was observed in the 3PA spectrum for excitation wavelengths with one-third of the energy (1200 nm) of the one-photon state.From the applications point of view, the nonlinear absorption spectrum can help to select the operation wavelength for a given device, indicating, for instance, the spectral region in which the nonlinear response is highest. Moreover, we also observed three-and four-photon excited fluorescence, suggesting MEH-PPV could be used as the active medium in up-conversion fluorescence devices. The multiphoton absorption features presented in this work combined with MEH-PPV's processability and commercial availability make it an interesting material for use in photonic devices. MEH-PPV has a p-p* absorption band around 490 nm, being completely transparent in the near-infrared region, as seen in Figure 1. Accordingly, nonlinear optical measurements were carried out under nonresonant excitation. Because of the asymmetry of MEH-PPV (highest symmetry C 2h ), [13] selectio...

Giant five-photon absorption from multidimensional core-shell halide perovskite colloidal nanocrystals

“…For the higher-order ησ 4 values, our NCs are ∼3–5 orders larger than the best reported results of organic chromophores162324 (see Supplementary Table 4). However, there are only limited research efforts devoted to studying the four-photon process in conventional inorganic semiconductor NCs.…”

Broadband three-photon absorption spectra of platinum acetylide complexes

“…2, all compounds present relatively high 3PA cross-section, in the order of 10 78 cm 6 s 2 photon 2 . Such values are comparable, although smaller, to the higher ones reported in the literature in near-infrared region [25,26]. The values observed for the optical nonlinearities are related to high transition dipole moments, μ eg and μ e'e , that are probably associated to the high planarity of the ground-state equilibrium geometry for compounds I and II, as well as to the presence of strong electron-donor and acceptor groups for compounds III and IV, respectively, in accordance with [12,20].…”

“…The 2PA spectra of this family of compounds cover the entire visible region [13], with peaks from 600 nm to 770 nm, depending on the compound. A similar enhancement behavior on the multi-photon absorption spectrum was also observed for polydiacetylenes [24] and MEH-PPV [25]. It is worth mentioning that the 2PA spectrum of the compounds studied here, at the near infrared (~850 nm), were determined to be approximately 40 GM.…”

Two-Photon Polymerization Fabrication of Doped Microstructures

“…For instance, in a methodology proposed by our group , poly (2-methoxy-5-2-ethylhexyloxy-1,4-phenylenevinylene) (MEH-PPV), widely known for its conductivity (Yu, et al,1995), electroluminescence (Nguyen, et al,2000, Parker,1994, and nonlinear optical properties (Chung, et al,2002, Correa, et al,2007, Oliveira, et al,2006 has been incorporated into the basic resin in a guesthost strategy. In the proposed methodology, the host consists of the two triacrylate monomers and the photoinitiator displayed in Fig.…”