Two‐Photon and Three‐Photon Absorption in an Organometallic Dendrimer

Abstract

Dedicated to Professor Gerhard Erker on the occasion of his 60th birthdayMultiphoton absorption is of intense interest for a variety of potential applications, such as optical power limiting, data storage, multiphoton microscopy, microfabrication, and frequency up-conversion lasing.[1] Multiphoton processes possess significant advantages, such as superior resolution, which enables precise spatial control for the various applications, together with the possibility of using infrared lasers at wavelengths that are technologically important in biology, medicine, and telecommunications. Thus far, most studies have considered two-photon absorption (2PA).[2] Enormous strides have been made in our understanding of how molecular structure controls 2PA efficiency by examining a range of compounds with dipolar, quadrupolar, and octupolar geometries. Three-photon absorption (3PA) may be superior to 2PA, because its cubic dependence on incident-light intensity leads to superior spatial confinement of the excitation volume and it also affords the possibility of using a much longer excitation wavelength. Whereas there have been several reports of three-photon processes resulting from 2PA followed by excited-state absorption (ESA), [3] there have been fewer studies of instantaneous 3PA [4] and very few examining the wavelength dependence of 3PA.[5] We report herein the first such study for an organometallic dendrimer and a record 3PA coefficient that highlights the potential of organometallic dendrimers.The synthesis of the dendrimer employed in the present study (1; dppe = 1,2-bis(diphenylphosphanyl)ethane) is described elsewhere.[6] The nonlinear absorption properties of 1 were evaluated by Z-scan experiments in the spectral range 625-1500 nm by employing fs pulses, the latter minimizing contributions from ESA and therefore giving a better prospect of affording the intrinsic nonlinearity; the short wavelength limit was chosen to ensure that all data were collected in the region of optical transparency of the dendrimer. Both closed-aperture and open-aperture Z-scan measurements were undertaken, thus permitting simultaneous evaluation of spectral dependences of both components of the complex hyperpolarizability (g real and g imag ); this is only the second such study for an inorganic compound. [7] The results for the range 625-950 nm are shown in Figure 1. Figure 1 reveals that g real is negative over this spectral range, whereas g imag is positive with a maximum at around [*] J.

Electron‐Rich Iron/Ruthenium Arylalkynyl Complexes for Third‐Order Nonlinear Optics: Redox‐Switching between Three States

“…For example, the lowest-energy intense transition in the NIR region is ipsochromically shifted by around 343 cm À1 (44 nm) when proceeding from 3-H + to 4 3 + . These modest shifts suggest that a similar assignment can be made for the various absorptions of this compound in its various oxidation states (4,4 3 + , 4 6 + ).…”

“…A dark-brown solid was again isolated that exhibits the same cyclic voltammogram as 3-HA C H T U N G T R E N N U N G [PF 6 ] but distinct spectral signatures (IR, UV/ Vis/NIR, and Mçssbauer). The isolated sample proved even more reactive than 4 ], which again limited its study in solution, although its UV spectrum was qualitatively similar to that observed in the OTTLE cell following dioxidation of 3-H. The IR spectrum of the isolated solid sample indicates the presence of a strong absorption at 1947 cm À1 and a second, weaker, band near 1845 cm À1 , which might be attributed to the two n CC stretches expected for this compound.…”

“…The efficiency and reversibility of each step were tested by applying a sufficiently positive potential to reoxidize the product; stable isosbestic points were observed in the spectral progressions for all the transformations reported herein. 1 4 ]A C H T U N G T R E N N U N G [PF 6 ]) at 25 8C at a platinum electrode using a SCE reference electrode and ferrocene as internal calibrant (0.460 V). [22] LSI/ESI-MS analyses were carried out at the Centre Regional de Mesures Physiques de l'Ouest (CRMPO, Rennes) on a high-resolution MS/MS ZabSpec TOF Micromass spectrometer (8 kV).…”

“…[3] In the field of nonlinear optics, carbonrich organometallics featuring organic ligands with extended unsaturated manifolds have attracted particular attention as a potentially interesting class of compounds for their thirdorder NLO properties. For example, large dendritic structures of this kind have been shown to have significant twophoton absorption cross-sections, [4] comparing very favorably with purely organic molecules of the same size. [5] Moreover, with redox-active trinuclear architectures such as 1 a (Scheme 1), which incorporates a single kind of metal center, it has been shown that the third-order response of these molecules can be switched in solution between two states under electrochemical control.…”

Mechanistic Investigations of Organic Aggregates with Different Topologies for Optical Limiting Applications

“…photon absorbers [37][38][39][40][41] Three-photon absorption cross-section is exceptionally strong for this organic molecule: . It is higher than those for best performing inorganic quantum dots 3-photon absorbers6 and 2 orders of magnitude higher than those for organic conjugated systems ( Figure 5).…”