Stereochemical Effects on Platinum Acetylide Two-Photon Chromophores.

A series of cis-platinum(II) acetylide complexes containing two-photon-absorbing chromophores have been synthesized and characterized to explore the effects of stereochemistry on the nonlinear absorption properties. The molecules feature 4-(phenylethynyl)phenylethynylene (PE2), diphenylaminofluorene (DPAF), and benzothiazolylfluorene (BTF) ligands. The photophysical properties were investigated under one- and two-photon conditions and compared to the known trans analogues via UV-visible absorption, photoluminescence, femtosecond and nanosecond transient absorption (TA), nanosecond z-scan, and femtosecond two-photon absorption (2PA). The bent cis complexes exhibit blue shifts in the absorption, emission, femtosecond, and nanosecond TA spectra along with lower molar extinction coefficients and lower phosphorescence yields relative to the trans complexes suggesting less efficient Pt-induced spin-orbit coupling and intersystem crossing in the cis configuration. The cis chromophores are noncentrosymmetric and therefore show dipolar behavior with a pronounced 2PA in the 0-0 transition of the S0 → S1 band, while the trans complexes show quadrupolar behavior with a forbidden 0-0 transition. In the S0 → Sn region, both cis and trans complexes show intense two-photon-absorption bands (up to 3700 GM by the peak cross section for cis-BTF) which contain a significant contribution from the excited state absorption (S1 → Sn). All six complexes exhibit comparable nonlinear absorption response with a significant contribution from triplet-triplet absorption that slightly favors trans complexes but is more strongly dependent upon the structure of the π-conjugated chromophore.

Polymer Monoliths Containing Two-Photon Absorbing Phenylenevinylene Platinum(II) Acetylide Chromophores for Optical Power Limiting.

A series of platinum(II) acetylide complexes containing p-phenylenevinylene and moieties end-capped with triphenylamine groups have been incorporated into poly(methyl methacrylate) (PMMA) monoliths for optical power limiting applications. The one- and two-photon photophysical properties were investigated and compared to the photophysical properties in THF. The absolute two-photon absorption cross-section values for the monolith samples were measured and are comparable to the values obtained in solution. In the PMMA monoliths, the complexes retained the important two-photon absorption and reverse saturable absorption properties necessary for optical power limiting via dual mode mechanism, and their strong nonlinear absorption property was demonstrated by the open-aperture Z-scan method. Photostability studies of the p-phenylenevinylene platinum(II) acetylide complexes showed two photodegradation processes: a trans-to-cis isomerization and a singlet-oxygen sensitized self-oxidative cleavage. The photostability of the least photostable complex TPV0 was increased upon incorporation into a PMMA matrix.

Photophysical properties of trans-platinum acetylide complexes featuring N-heterocyclic carbene ligands.

A series of trans-N-heterocyclic carbene (NHC) platinum(ii) acetylide complexes of the form (ICy)2Pt(R)2 (where ICy = 1,3-bis-(cyclohexyl)imidazol-2-ylidene and R = 1-Ethynyl-4-(phenylethynyl)benzene (PE2), 2-(9,9-Diethyl-9H-fluoren-7-yl)benzo[d]thiazole (BTF), and 9,9-Diethyl-7-ethynyl-N,N-diphenyl-9H-fluoren-2-amine (DPAF), respectively), were synthesized via Hagihara reaction of the unprotected aryl-acetylide ligands with trans-(ICy)2PtCl2 () in 47-73% yield. Precursor was generated in a one-pot synthesis via formation of a silver carbene precursor followed by transmetallation, and was obtained in high yield (95%). The single-crystal X-ray structures of , were determined and analyzed. The photophysical properties of were compared to their respective tributyl phosphine (PBu3) analogues. The optical properties of the series were studied by UV-Vis spectroscopy, photoluminescence spectroscopy, nanosecond transient absorption spectroscopy, and open aperture nanosecond z-scan. Coupling of the organic chromophores to the platinum center affords efficient intersystem crossing as concluded by the complexes' low fluorescence quantum yields, efficient phosphorescence and intense T1 - Tn absorption. Open aperture z-scan with 606 nm, 10 ns laser pulses showed comparable optical attenuation relative to a standard sample of (PBu3)2Pt(DPAF)2 (). Pulse limiting was achieved via a dual-mechanism of two-photon absorption (2PA) coupled with excited-state absorption (ESA). TD-DFT Computations were also employed for to give greater insight into the nature of the singlet-singlet electronic transitions.

Phenylene vinylene platinum(II) acetylides with prodigious two-photon absorption.

The linear and nonlinear optical properties of a series of linear and cross-conjugated platinum(II) acetylide complexes that contain extended p-(phenylene vinylene) chromophores are reported. The complexes exhibit very high femtosecond two-photon absorption (2PA) cross section values (σ(2) up to 10,000 GM), as measured by nonlinear transmission (NLT) and two-photon excited fluorescence (2PEF) methods. The large 2PA cross sections span a broad range of wavelengths, 570-810 nm, and they overlap with the triplet excited state absorption. Spectral coincidence of high cross section 2PA and triplet absorption is a key feature giving rise to efficient dual-mode optical power limiting (OPL).

Active trifluoromethylating agents from well-defined Copper(I)-CF3 complexes.

The first examples of isolable and structurally characterized Cu(I)-CF3 complexes are reported. N-Heterocyclic carbene (NHC)-supported copper tert-butoxide complexes reacted with Me3Si-CF3 to afford new (NHC)Cu-CF3 complexes whose structures were dependent on whether or not the C4-C5 positions of the five-membered NHC rings were saturated. In situ generated (SIiPr)Cu-CF3 cleanly transferred its trifluoromethyl group to a number of organic halides under mild conditions.