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The fabrication, molecular structure, and spectroscopy of a stable cholesteric liquid crystal platinum acetylide glass obtained from trans-Pt(PEt3)(2)(C(sic)C-C6H5-C(sic)N)(C(sic)C-C6H5-COO-Cholesterol), are described and designated as PE1-CN-Chol. Polarized optical microscopy, differential scanning calorimetry, and wide-angle X-ray scattering experiments show room temperature glassy/crystalline texture with crystal formation upon heating to 165 degrees C. Further heating results in conversion to cholesteric phase. Cooling to room temperature leads to the formation of a cholesteric liquid crystal glass. Scanning tunneling microscopy of a PE1-CN-Chol monolayer reveals self-assembly at the solid-liquid interface with an array of two molecules arranged in pairs, oriented head-to-head through the CN groups, giving rise to a lamella arrangement. The lamella structure obtained from molecular dynamics calculations shows a clear phase separation between the conjugated platinum acetylide and the hydrophobic cholesterol moiety with the lamellae separation distance being 4.0 nm. Ultrafast transient absorption and flash photolysis spectra of the glass show intersystem crossing to the triplet state occurring within 100 ps following excitation. The triplet decay time of the film compared to aerated and deoxygenated solutions is consistent with oxygen quenching at the film surface but not within the film. The high chromophore concentration, high glass thermal stability, and long triplet lifetime in air show that these materials have potential as nonlinear absorbing materials., QC 20210915

To prepare cholesteric liquid crystalline nonlinear optical materials with ability to be vitrified on cooling and form long time stability cholesteric glasses at room temperature, a series of platinum acetylide complexes modified with cholesterol has been synthesized. The materials synthesized have the formula trans-Pt(PR3)(cholesterol (3 or 4)-ethynyl benzoate)(1-ethynyl-4- X-benzene), where R = Et, Bu or Oct and X = H, F, OCH3 and CN. A cholesteric liquid crystal phase was observed in the complexes R = Et, and X = F, OCH3 and CN but not in any of the other complexes. When X = CN, a cholesteric glass was observed at room temperature which remained stable up to 130 oC, then converted to a mixed crystalline/cholesteric phase and completely melted to an isotropic phase at 230 oC. When X = F or OCH3 the complexes were crystalline at room temperature with conversion to the cholesteric phase upon heating to 190 and 230 oC, respectively. In the series X = CN, OCH3 and F, the cholesteric pitch was determined to be 1.7, 3.4 and 9.0 , respectively., Prepared in collaboration with Centro de Investigacion en Quimica Aplicada (CIQA), Saltillo, Coahuila, Mexico, the Department of Chemistry, University of Dayton, Dayton, OH, and the Department of Physics, University of Colorado at Colorado Springs. Sponsored in part by AFOSR.

We study instantaneous two-photon absorption (2PA) in a series of nominally quasi-centrosymmetric trans-bis (tributylphosphine)-bis-(4-((9,9- diethyl-7-ethynyl-9H-fluoren-2-yl) ethynyl)-R)-platinum complexes, where 11 different substituents, R = N(phenyl)2(NPh2), NH2, OCH3, tbutyl, CH3, H, F, CF3, CN, benzothiazole, and NO2, represent a range of electron-donating (ED) and electron-withdrawing (EW) strengths, while the Pt core acts as a weak ED group. We measure the 2PA cross section in the 540 810 nm excitation wavelength range by complementary femtosecond twophoton excited fluorescence (2PEF) and nonlinear transmission (NLT) methods and compare the obtained values to those of the Pt-core chromophore and the corresponding noncentrosymmetric side group (ligand) chromophores. Peak 2PA cross sections of neutral and ED-substituted Pt complexes occur at S0 Sn transitions to higher energy states, above the lowest-energy S0 S1 transition, and the corresponding values increase systematically with increasing ED strength, reaching maximum value, 2 300 GM (1 GM = 10 50 cm4 s), for R = NPh2. At transition energies overlapping with the lowest-energy S0 S1 transition in the one-photon absorption (1PA) spectrum, the same neutral and ED-substituted Pt complexes show weak 2PA, 2 30 100 GM, which is in agreement with the nearly quadrupolar structure of these systems. Surprisingly, EW-substituted Pt complexes display a very different behavior, where the peak 2PA of the S0 S1 transition gradually increases with increasing EW strength, reaching values 2 = 700 GM for R = NO2, while in the S0 Sn transition region the peak 2PEF cross section decreases. We explained this effect by breaking of inversion symmetry due to conformational distortions associated with low energy barrier for ground-state rotation of the ligands., The original document contains color images.

To explore the photophysics of platinum acetylide chromopores having strong two photon cross section, we have investigated the synthesis and spectroscopic characterization of a series of platinum acetylide complexes that feature highly π-conjugated ligands substituted with π-donor or ?acceptor moieties. The molecules (numbered 1-4) considered in the present work are NLO-functionalized analogs of bis(phenylethynyl)bis(bributylphosphine)platinum(II) complexes. Molecule 1 carries two benzothiazolylfluorene and molecule 2 carries two diphenylaminofluorene substituents bound to the central platinum atom. Compounds 3 and 4 possess two dihexylaminophenyl substituents at their ends and differ by the number of platinum atoms in the oligomer ?core? (one vs. two in 3 and 4, respectively). The conjugated ligands impart the complexes with effective two-photon absorption cross sections, while the heavy metal platinum centers give rise to efficient intersystem crossing to afford long lived triplet states. Photophysical studies demonstrate that one-photon excitation of the chromophores produces and S1 state that is delocalized across the two conjugated liglands, with weak (excitonic) coupling through the platinum center(s). The S1 state is observed by ultrafast transient absorption and by its characteristic fluorescence. Intersystem crossing occurs rapidly (kisc ≈ 1011 s-1) to produce the T1 state, which is believed to be localized on a single conjugated fluorenyl ligand. The triplet state is strongly absorbing (εTT > 5 x 104 M-1cm-1) and it is very long-lived (τ > 100 μs). Femtosecond pulses were used to characterize the two-photon absorption properties of the complexes, and all of the chromophores are relatively efficient two photon absorbers in the visible and near-infrared region of the spectrum (600 ? 800 nm). The complexes exhibit maximum, Pub. in Chemistry of Materials

To explore the photophysics of platinum acetylide chromopores having strong two-photon absorption cross-sections, we have investigated the synthesis and spectroscopic characterization of a series of platinum acetylide complexes that feature highly pi-conjugated ligands substituted with pi-donor or -acceptor moieties. The molecules (numbered 1-4) considered in the present work are NLO-functionalized analogs of bis(phenylethynyl)bis(bributylphosphine)platinum(II) complexes. Molecule 1 carries two benzothiazolylfluorene and molecule 2 carries two diphenylaminofluorene substituents bound to the central platinum atom. Compounds 3 and 4 possess two dihexylaminophenyl substituents at their ends and differ by the number of platinum atoms in the oligomer "core" (one vs. two in 3 and 4, respectively). The conjugated ligands impart the complexes with effective two-photon absorption cross sections, while the heavy metal platinum centers give rise to efficient intersystem crossing to afford long lived triplet states. Photophysical studies demonstrate that one-photon excitation of the chromophores produces and S1 state that is delocalized across the two conjugated ligands, with weak (excitonic) coupling through the platinum center(s). The S1 state is observed by ultrafast transient absorption and by its characteristic fluorescence. Intersystem crossing occurs rapidly (k sub isc) approx. 1011/s)) to produce the T(sub 1) state, which is believed to be localized on a single conjugated fluorenyl ligand. The triplet state is strongly absorbing (epsilon (sub TT) > 50,000/M/cm)) and it is very long-lived (tau > 100 microsecs). Femtosecond pulses were used to characterize the two-photon absorption properties of the complexes, and all of the chromophores are relatively efficient two photon absorbers in the visible and near-infrared region of the spectrum (600 - 800 nm)., Pub. in Inorganic Chemistry, v46 n16, p6483-6494, 2007.

To prove the source of ground state self-quenching in trans-Pt(P(P(C8H17)3)2(C=CC6H4C=CC6H5)2 is a result of triplet excimer formation, we carried out nanosecond transient absorption measurements on multiple concentrations. By constructing a kinetic model for the system we were able to determine rate constants for the formation and decay of the triplet excimer, 4.7 x 106 M-1s-1 and 6.9 x 105 s-1 respectively. We determined the transient absorption spectrum for the excimer which has an extinction coefficient maximum per excimer unit of 95,680 M-1cm1 at 600nm. Experimental analysis suggests that the formation of the triplet excimer is largely due to a ligand to ligand interaction., Submitted for publication in Chemistry of Materials. Prepared in collaboration with AT&T Government Solutions, Dayton, OH; General Dynamics Information Technology, Inc., Dayton, OH; UES, Dayton, OH; and Science Applications International Corporation (SAIC), Dayton, OH.

As part of an ongoing investigation of structure-optical property relationships in platinum acetylide complexes, we synthesized the compounds trans-Pt(PBU3)2(C=CC6HS)(C=C-C6H4-C=CC6HS)(PE 1-2), trans- Pt(PBU3h( C=CC6HS)(C=CC6H4-C=C-C6~-C=CC6Hs)(PEl-3) and trans-Pt(PBU3h(C=C-C6~-C=CC6Hs)(C=CC6H4-C=C-C6H4-C=CC6Hs)(PE2-3)that have different ligands on either side of the central platinum and compared their spectroscopic properties to the symmetrical compounds PE1, PE2 and PE3. We measured trends in ground state absorption, fluorescence, phosphorescence and triplet state absorption spectra. We also performed density functional theory calculations of the triplet state geometries and energies. The ground state absorption and fluorescence spectra give evidence the singlet exciton is delocalized across the central platinum atom. In contrast, the behavior of the phosphorescence spectra suggests the triplet exciton is confined to one ligand. The phosphorescence from the asymmetric complexes comes from the lowest energy, most delocalized ligand. The triplet state geometries obtained from the density functional theory calculations show distortion on the lowest energy ligand, while the other ligand has the ground state geometry. The calculated trend in the triplet state energies agrees very well with the experimental trend. Calculations of triplet state spin density also show the triplet exciton is confined to one ligand. In the asymmetric complexes the spin density is confined to the more conjugated, lower energy ligand. The results show Kasha's rule applies to these complexes, where following excitation and intersystem crossing, the triplet exciton moves to the lowest energy ligand., Prepared in collaboration with General Dynamics Information Technology, Inc., Dayton, OH, Science Applications International Corp., Dayton, OH, UES, Inc., Dayton, OH and AT&T Corporation Government Solutions, Dayton, OH.