Simultaneous Observation of Green Multiphoton Upconversion and Red and Blue NLO Processes from Polymeric Terbium(III) Complexes

Abstract

Photoexcitation at a certain wavelength in the near-infrared (NIR) region followed by luminescence at a shorter wavelength in the visible domain is called near-infrared-to-visible photon upconversion. This is a rather unusual process as lowenergy photons are "converted" into higher energy photons: two or three photons of NIR light are required to generate one photon of visible light.[1] Nonlinear optics (NLO) is another mechanism that can lead to the generation of light at a frequency that is either twice or integral-multiples of the incident light.[2] The phenomena of two-or three-photon upconversion, and second or third harmonic generation (SHG or THG) on organic materials have received considerable attention since fluorescence detection became popular in applications such as photodynamic therapy, optical data storage, and microfabrication. [3] Multiphoton excitation allows molecules that typically absorb in the UV region to be excited with red or NIR light. The photoluminescence processes from organolanthanide complexes are usually induced by an organic chromophoric ligand that absorbs incident light and transfers its resultant excitation energy to the lanthanide ion.[4] Until now, only a few multiphoton processes in organolanthanide complexes have been observed owing to the limitations of experimental measurements.[5] Although there have been reports on lanthanide complexes that display second harmonic generation, these have been limited and focused only on glassy doped lanthanide materials.[6] In recent years, our group [7] and others [8] have investigated several high-order multiphoton processes from organic ligands and metal complexes. Herein we report, to the best of our knowledge, the first observation of rare multiphoton upconversion emission from a lanthanide complex as well as SHG and THG transmission phenomena, which occur simultaneously from the same excitation source in the IR region at l % 1.26 and 1.34 mm.The N-tripodal ligand L was treated with terbium nitrate to give the complex [Tb(L)(NO 3 ) 3 ] (1, see Figure 1), which is thermally stable up to 300 8C, as shown by thermogravimetric analysis (see Supporting Information). Single crystals of 1 were isolated through the slow evaporation of a solution of 1 in THF/MeCN at room temperature over a few days. The crystal structure of 1 was determined by X-ray crystallography and is shown in Figure 2. The coordination geometry of the metal center in 1 can be described as a tricapped trigonal prism, in which each Tb 3+ ion is coordinated by three carbonyl (amide) groups from three separate but identical tripodal ligands, and doubly coordinated by three nitrate ions. Upon complexation, the tripodal ligand adopts a polymetallic dendritic form, as the branches contain oxygen groups for binding with lanthanide ions. The ensemble of the tripodal ligand and its connectivity with the lanthanide ion, which itself is preorganized as a result of its coordination to three chromophores, forms a metallodendrimer. The metal takes on a "metal as ligand, metal as co...

Lanthanide luminescence for functional materials and bio-sciences

“…480 To close this short overview of MPA phenomena in lanthanide complexes, we would like to mention the polymeric Tb III complex [Tb(NO 3 ) 3 (57c)] n , which upon laser excitation at 1.26 mm exhibits green Tb III emission from a 4PA process as well as blue and red emission resulting from single and third harmonic generation, the complex playing the role of the gain medium. 481 Two-photon excitation luminescence microscopy is a relatively new technique which started in the 1990s. 482 Besides using a ''cell-friendly'' NIR excitation wavelength, it allows the imaging of difficult samples with good resolution.…”

Nonlinear optical activity in dipolar organic–lanthanide complexes

“…The first series of lanthanide complexes (Type I) with La (1), Ce (2), Nd (4), Sm ( 5), Eu (6), Gd (7) and Tb (8), where the ionic radius of Ln 3+ is between 103 and 92 pm, crystallize in the trigonal system R3c (Fig. 3, Type I) and the other seven complexes (Type II) comprise Dy (9), Y (10), Ho (11), Er (12), Tm (13), Yb (14) and Lu (15), where the ionic radius of Ln 3+ is between 91 and 86 pm, and crystallize in the primitive monoclinic system P2 1 (Fig. 3, Type II).…”

“…[10][11][12] We have reported a novel system for which multiphoton absorption produced second and third harmonic generation (SHG and THG) simultaneously with intraconfigurational 4f emission. 13,14 The variations in coordination geometry of the central metal atom, and also the ligation of carboxylate ions in lanthanide carboxylate complexes, are both interesting themes of structural chemistry. [15][16][17] Over the past twenty years, many structural studies of lanthanide carboxylates have been reported, where diverse coordination types have been recognized.…”

A two‐photon europium complex as specific endoplasmic reticulum probe

“…The photoluminescence processes from organic-lanthanide complexes are usually induced by an organic chromophoric ligand that absorbs light and transfers this excitation energy to the lanthanide ion [6], [13,14]. In recent years, limited numbers of organic-terbium complexes have been reported for in-vitro imaging with low two-photon quantum efficiency, for example, a Tb III -protein complex for in-vitro imaging with 20 GM at 800 nm [5], and our recently reported Tb-polymeric tripodal amide complex showing values of $2.6 GM in the spectral region of 800 nm [4].…”