Two-Photon Absorption-Related Properties of Functionalized BODIPY Dyes in the Infrared Range up to Telecommunication Wavelengths

✍ Scribed by Pierre-Antoine Bouit; Kenji Kamada; Patrick Feneyrou; Gérard Berginc; Loïc Toupet; Olivier Maury; Chantal Andraud

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 262 KB
• Volume: 21
• Category: Article
• ISSN: 0935-9648
• DOI: 10.1002/adma.200801778

✦ Synopsis

Two-photon absorption (TPA) is a resonant third-order nonlinear optical (NLO) process in which an electron is promoted from its ground state to an excited state by simultaneous absorption of two photons of half-energy in an intense focused light beam such as that generated by a laser source. This phenomenon, theoretically predicted in 1929 by Go ¨ppert-Mayer, [1] was experimentally evidenced in 1961 in a TPA-induced fluorescence of Eu 2þ -doped CaF 2 crystals under ruby-laser irradiation. [2] Since then, the intrinsic advantages of TPA excitation, that is, long wavelength and confocal 3D-resolved absorption, led to numerous applications in the fields of material sciences and biology following the availability of tunable laser sources. In particular, the development of femtosecond (fs)-Ti-sapphire lasers triggered numerous studies in the 700-1000 nm spectral range. For instance, TPA was successfully involved in the fabrication of microstructures [3,4] or high-density optical memories [5] with a 3D sub-micrometer resolution, in signal processing, or for the design of optical limiting devices devoted to the protection of sensors against laser damages. [6,7] In life sciences, the long-wavelength TPA excitation is located in the biologically transparent spectral range (800-1000 nm), and is therefore able to penetrate more deeply into biological tissues. Combined with the above mentioned spatial resolution, TPA found exciting applications for bioimaging using nonlinear microscopy, [8] and also for drug delivery or dynamic phototherapy. [9] All these applications encouraged the scientific community to design a large variety of chromophores with optimized two-photon cross-sections (s 2 ) in this 700-1000 nm spectral range, such as organic dyes, organometallic or coordination complexes, polymers, dendrimers, or nanonoparticles and quantum-dots, compiled in a recent exhaustive review. [10] However, the near-infrared (NIR) spectral range has been less studied, and in particular the telecommunications-wavelengths spectral range (1.3-1.55 mm), where applications in signal processing (optical power stabilization, pulse suppression, optical limiting) are very attractive. Since 2005, inspired by the Marder-Van Stryland and Osuka-Kim groups, there is a great interest in the design of chromophores exhibiting strong TPA properties in the NIR. Maximal TPA cross-section of ca. 1500 GM at 1.44 mm and 1600 GM at 1.3 mm have been reported for dipolar and quadrupolar squarine-type chromophores, respectively, [11,12] whereas nickel (bisdithiolene) complexes [13] and singlet diradical systems [14] exhibit significant s 2 over the entire telecommunication range. On the other hand, numerous fused-, extended-, or organizedporphyrin complexes have been reported with very large TPA crosssections ranging from 10 3 to 10 4 GM. [15][16][17][18][19] Finally, we reported the TPA properties of cyanine-type chromophores (s 2 of 750 GM at 1450 nm) that present enough solubility to carry out additional nonlinear transmittance experiments at telecommunications wavelengths. [20] Herein, we report the synthesis and X-ray structures of aza boron-dipyrromethane (Bodipy) NIR dyes functionalized in the a position by donor-p-conjugated systems, and their TPA and nonlinear transmittance properties in the 1.2-1.6 mm spectral range.

It is worth noting that Bodipy dyes are a versatile class of chromophores [21][22] largely studied for its exceptional luminescence properties, and are used as biomolecular labels, sensors (pH, NO, Hg 2þ , toxin. . .), or photonic therapeutic agents. [21][22][23][24][25][26] Great efforts have been recently devoted to shift their spectroscopic properties to the NIR spectral range by i) introduction of electrondonating moieties, [27] ii) rigidification of the structure, [28] or iii) replacement of the meso-carbon by a nitrogen atom (the ''aza''-Bodipy). [29][30][31] But surprisingly, whereas water-soluble conventional Bodipy dyes featuring low two-photon cross-sections were used for two-photon imaging microscopy, [32,33] these compounds were not fully optimized for TPA applications. To the best of our knowledge, only multi-chromophoric dyes containing two or three Bodipy units and exhibiting rather modest s 2 values (75 GM at 990 nm) in the visible were described in the literature. [34] The synthesis of the target chromophores B 1-2 (Scheme 1), featuring an extended p-conjugated skeleton, involves as key step COMMUNICATION www.advmat.de

[*] Dr.