Synthetically Tunable White-, Green-, and Yellow-Green-Light Emission in Dual-Luminescent Gold(I) Complexes Bearing a Diphenylamino-2,7-fluorenyl Moiety.

The syntheses and photophysical characterization of five new gold(I) complexes bearing diphenylamine-substituted fluorenyl moieties are reported; four are characterized by X-ray diffraction crystallography. Ancillary ligation on gold(I) is provided by organophosphine and N-heterocyclic carbene ligands. Two complexes, Au-DPA0 and Au-DPA1, are σ-aryls, two, Au-ADPA0 and Au-ADPA1, are σ-alkynyls, and one, Au-TDPA1, is a σ-triazolyl bound through carbon. All complexes show vibronically structured absorption and luminescence bands that are assignable to π-π* transitions localized on the diphenylamine-substituted fluorenyl π system. The excited-state dynamics of all five chromophores are governed by selection of the ancillary ligand and σ attachment of the diphenylamine-substituted fluorenyl moiety. All of these chromophores are dual luminescent in a toluene solution at 298 K. The luminescence from the aryl derivatives, Au-ADPA0 and Au-DPA1, appears green. The alkynyl derivative containing a phosphine ancillary ligand, Au-ADPA0, is a white-light emitter, while the alkynyl derivative containing an N-heterocyclic carbene ancillary ligand, Au-ADPA1, is a yellow-light emitter. The luminescence from the triazolyl-linked chromophore, Au-TDPA1, appears as yellow-green. Spin-restricted density functional theory calculations support the assignments of ligand-centric optical transitions but with contributions of ligand-to-metal charge transfer involving the vacant Au 6p orbital.

Two-photon absorption characterization and comparison of Au(I) fluorenyl benzothiazole complexes in the visible wavelength regime.

We use the two-photon excited fluorescence method to determine the two-photon absorption (2PA) cross sections of three series of (fluorenyl benzothiazole) gold(I) complexes in the visible wavelength range from 570 to 700 nm. We compare the effect of ancillary ligand substitutions on the 2PA magnitudes and find that the ancillary ligand does not drastically affect either the magnitude or the shape of 2PA. Even so, moderate 2PA cross sections were measured that ranged from 10 to 1000 s of GM (Göppert-Mayer, =10-50cm4s/photon), making these types of complexes nonlinear optical materials for two-photon absorbing applications.

Synthesis and photophysics of gold(i) alkynyls bearing a benzothiazole-2,7-fluorenyl moiety: a comparative study analyzing influence of ancillary ligand, bridging moiety, and number of metal centers on photophysical properties.

Three new gold(i) alkynyl complexes (Au-ABTF(0-2)) containing a benzothiazole fluorenyl moiety, with either an organic phosphine or N-heterocyclic carbene as ancillary ligand, have been synthesized and photophysically characterized. All three complexes display highly structured ground-state absorption and luminescence spectra. Dual-luminescence is observed in all three complexes at room temperature in toluene after three freeze-pump-thaw cycles. The phosphine complexes (Au-ABTF(0-1)) exhibit similar photophysics with fluorescent quantum yields ∼0.40, triplet-state quantum yields ∼0.50, and fluorescent lifetimes ∼300 ps. The carbene complex Au-ABTF2 displays different behavior; having a fluorescent quantum yield of 0.23, a triplet-state quantum yield of 0.61, and a fluorescent lifetime near 200 ps, demonstrating that the ancillary ligand alters excited-state dynamics. The compounds exhibit strong (on the order of 105 M-1 cm-1) and positive excited-state absorption in both their singlet and triplet excited states spanning the visible region. Delayed fluorescence resulting from triplet-triplet annihilation is also observed in freeze-pump-thaw deaerated samples of all the complexes in toluene. DFT calculations (both static and time-resolved) agree with the photophysical data where phosphine complexes have slightly larger S1-T2 energy gaps (0.28 eV and 0.26 eV) relative to the carbene complex (0.21 eV). Comparison of the photophysical properties of Au-ABTF(0-2) to previously published dinuclear gold(i) complexes and mononuclear gold(i) aryl complexes bearing the same benzothiazole-2,7-fluorenyl moiety are made. Structure-property relationships regarding ancillary ligand, bridging moiety, and number of metal centers are drawn.

Anion-Cation Mediated Structural Rearrangement of an In-derived Three-Dimensional Interpenetrated Metal-Organic Framework.

Postsynthetic modification of metal-organic frameworks (MOFs) has proven an effective method of synthesizing architectures that have proven challenging to produce via classic solvothermal means. Herein we report the anion-cation assisted solid-state transformation of a three-dimensional MOF (ATF-1) to a series of two-dimensional structures (YCM-21-Z) via treatment with quaternary ammonium halides. It is important to note that this reaction requires no exogoneous building blocks (inorganic cation and/or organic linker) for conversion to occur. This reaction led to the synthesis of a chemically unique framework YCM-21-Bnpy in which phase-pure synthesis cannot be achieved by solvothermal means. The mechanism of transformation was studied with data supporting a nucleophilic halide (Br, Cl, or F) mediated de-intercalation and cation-assisted flattening of the In secondary building unit as the key mechanistic steps.

Photophysical properties of organogold(i) complexes bearing a benzothiazole-2,7-fluorenyl moiety: selection of ancillary ligand influences white light emission.

Herein we report three new gold(i) complexes with a benzothiazole-2,7-fluorenyl moiety bound through a gold-carbon σ-bond and either an N-heterocyclic carbene or organophosphine as ancillary ligands. The complexes have been characterized by NMR spectroscopy, X-ray crystallography, high resolution mass spectrometry, elemental analysis, and static and time-resolved optical spectroscopy. These compounds absorb almost strictly in the ultraviolet region and exhibit dual-luminescence following three freeze-pump-thaw cycles in toluene. The selection of the ancillary ligand significantly influences the excited-state dynamics of the complexes. The two phosphine containing complexes have similar fluorescence and phosphorescence quantum yields leading to generation of white light emission. The carbene containing complex exhibits a higher fluorescence quantum yield compared to its phosphorescence quantum yield resulting in a violet emission. Extensive photophysical characterization of these compounds suggests that the phosphine complexes undergo intersystem crossing more efficiently than the carbene complex. This is supported by a three-fold increase in luminescence lifetime, a halving in fluorescence quantum yield, and an increase in intersystem crossing efficiency by 25 percent for the phosphine complexes. Density-functional theory calculations support these observations where the energy gap between the S1 and T2 states for the carbene is roughly twice that of the phosphine complexes. To our knowledge this is the first example of single-component mononuclear gold(i) complexes exhibiting non-excimeric state white light emission, although a similar phenomenon has been realized for gold(iii) aryl compounds. Further, the triplet lifetimes of all three complexes are on the order of one ms in freeze-pump-thaw degassed toluene. These molecules also exhibit delayed fluorescence; all of the complexes display diffusion-controlled rate constants for triplet-triplet annihilation. Strong excited-state absorption is observed from the singlet and triplet excited-states in these molecules as well. The singlet states have excited-state extinction coefficients on the order of 1.5 × 105 M-1 cm-1 and the triplet states have excited-state extinction coefficients on the order of 1.0 × 105 M-1 cm-1.