No abstract

Original nanocomposites have been obtained by direct incorporation of pre-synthesized oleic acid capped TiO(2) nanorods into properly functionalized poly(methyl methacrylate) copolymers, carrying carboxylic acid groups on the repeating polymer unit. The presence of carboxylic groups on the alkyl chain of the host functionalized copolymer allows an highly homogeneous dispersion of the nanorods in the organic matrix. The prepared TiO(2)/PMMA-co-MA nanocomposites show high optical transparency in the visible region, even at high TiO(2) nanorod content, and tunable linear refractive index depending on the nanoparticle concentration. Finally measurements of nonlinear optical properties of TiO(2) polymer nanocomposites demonstrate a negligible two-photon absorption and a negative value of nonlinear refractive index, highlighting the potential of the nanocomposite for efficient optical devices operating in the visible region.

Picosecond nonlinear absorption dynamics of neutral metal-dithiolenes belonging to the general class [M(R,R′timdt)2] (M=Ni, Pd, Pt; R,R′ timdt=monoreduced form of disubstituted imidazolidine-2,4,5-trithione) has been investigated at λ=1064 nm using the pump–probe technique. Both central metal ion M and substituents R,R′ have been found to strongly influence the temporal evolution of the absorption saturation. In particular, it has been observed that the intersystem crossing rate always increases by a factor ∼1.5 when changing the central metal from Pd to Pt. The mechanisms leading to the measured dynamics have been explained using a multilevel rate equation analysis, based on the results of relativistic time-dependent density functional calculations.

With the aim of preparing new dyes for Q‐switching and/or mode‐locking Nd‐based lasers, such as Nd:YLF and Nd:YAG (emission wavelengths 1053 and 1064 nm, respectively), the syntheses of about 30 new neutral dithiolenemetal complexes belonging to the class [M(R,R′timdt)2] have been carried out [M = Ni (4a−c; 4g−j), Pd (5a−j), Pt (6a−j); R,R′timdt = monoreduced form of disubstituted imidazolidine‐2,4,5‐trithione]. The examination of the effects induced on the intense NIR absorption by changing M, R, and R′ has allowed for the recognition of the additive contributions (Δλ) of the central metal ion and of the substituents to the λM,R,R′max position of the NIR absorption maximum, which is in the region of 1000 nm. The high Δλ values due to aromatic substituents have been elucidated by means of Hybrid‐DFT calculations performed on the model compound [Ni(H2timdt)(Ph,H‐timdt)]. Both the λM,R,R′max values and the molar extinction coefficients vary with the solvent. Complex 5f [M = Pd, R = p‐F‐C6H4, R′ = m,m,p‐(MeO)3‐C6H2] shows that it has been possible to exactly match the emission wavelength of the Nd:YLF and Nd:YAG lasers in chloroform and toluene, respectively (by choosing the appropriate combination of metal ion and substituents). The highest extinction coefficient ever observed for a metal‐dithiolene (120000 M−1·cm−1 at 1034 nm in toluene) is also reported for complex 6g [M = Pt, R = p‐F‐C6H4, R′ = naphthyl]. Time‐resolved absorption dynamics measurements on 5f have also been carried out by means of pump‐probe experiments, with a picosecond Nd:YAG Q‐switched and mode‐locked laser. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

No abstract