Showing their true colors? Full emission color tuning in the visible region can be achieved with salen-aluminum complexes that are electronically modulated at C5 of the phenoxide ring in the salen moiety. Emission spectra for various substituents R(5) are shown (EWG: electron-withdrawing group, EDG: electron-donating group).A series of salen-aluminum complexes, [{(R(5))(2)-salen(3-tBu)(2)}Al(OC(6)H(4)-p-C(6)H(5))] (salen=N,N'-bis(salicylidene)ethylenediamine; R(5)=H (1), tBu (2), Br (3), Ph (4), OMe (5), NMe(2) (6)) and [{5,5'-(NMe(3))(2)-salen(3-tBu)(2)}Al(OC(6)H(4)-p-C(6)H(5))][OTf](2) (7; OTf=CF(3)SO(3)) that are electronically modulated directly at C5 of the phenoxide ring in the salen moiety has been prepared. The crystal structures of 1, 4, 6, and 7 determined by X-ray diffraction reveal distorted square-pyramidal geometries around the Al atoms. Complexes 1-7 are all air-stable in both the solid and solution states and have high thermal stability (decomp 313-338 degrees C). Differential scanning calorimetric analyses show that they can form amorphous glasses with glass transition temperatures of 95-132 degrees C depending on the C5 substituent. UV/Vis absorption spectra of the complexes exhibit major bands at lambda=338-413 nm assignable to salen-centered pi-pi* transitions with a gradual red shift of the absorption maximum wavelengths as the substituent is varied from an electron-withdrawing (NMe(3)) to an electron-donating group (NMe(2)). The maxima in the emission spectra of 1-7 occur over the entire visible region, ranging from lambda=438 nm for 7 to lambda=599 nm for 6, with high fluorescence quantum efficiencies of up to Phi=0.40 for 4 in solution. DFT calculations suggest that the low-energy electronic transitions in 1-7 are characterized by HOMO(-i)-LUMO(+1) (i=1 for 1-6 or i=4 for 7) transitions localized on the salen moiety, with much involvement of the C5 position in the HOMO(-i). Thus, the electronic alteration at the C5 position of the phenoxide ring, which mainly affects the HOMO(-i) energy levels of salen-Al luminophores, is responsible for the observed emission color-tuning properties over the entire visible region.
Structures and vibrational frequencies of group 17 fluorides EF3 (E = I, At, and element 117) are calculated at the density functional theory (DFT) level of theory using relativistic effective core potentials (RECPs) with and without spin-orbit terms in order to investigate the effects of spin-orbit interactions and electron correlations on the structures and vibrational frequencies of EF3. Various tests imply that spin-orbit and electron correlation effects estimated presently from Hartree-Fock (HF) and DFT calculations with RECPs with and without spin-orbit terms are quite reasonable. Spin-orbit and electron correlation effects generally increase bond lengths and/or angles in both C2v and D3h structures. For IF3, the C2v structure is a global minimum, and the D3h structure is a second-order saddle point in both HF and DFT calculations with and without spin-orbit interactions. Spin-orbit effects for IF3 are negligible in comparison to electron correlation effects. The D3h global minimum is the only minimum structure for (117)F3 in all RECP calculations, and the C2v structure is neither a local minimum nor a saddle point. In the case of AtF3, the C2v structure is found to be a local minimum in all RECP calculations without spin-orbit terms, and the D3h structure becomes a local minimum at the DFT level of theory with and without spin-orbit interactions. In the HF calculation with spin-orbit terms, the D3h structure of AtF3 is a second-order saddle point. AtF3 is a borderline case between the valence-shell-electron-pair-repulsion (VSEPR) structure of IF3 and the non-VSEPR structure of (117)F3. Relativistic effects, including scalar relativistic and spin-orbit effects, and electron correlation effects together or separately stabilize the D3h structures more than the C2v structures. As a result, one may suggest that the VSEPR predictions agree very well with the structures optimized by the nonrelativistic HF level of theory even for heavy-atom molecules but not so well with those from more elaborate theoretical methods. Vibrational frequencies of AtF3 and (117)F3 are modified substantially and nonadditively by spin-orbit and electron correlation contributions. This is one of those rare cases for which vibrational frequencies of the closed-shell molecules are significantly affected by spin-orbit interactions. Spin-orbit interactions decrease all vibrational frequencies of EF3 molecules considered.
Several theoretical studies have suggested that a spin-orbitinduced isomer may be found for a molecule of the as-yetunknow superheavy element 118, that is, (118)F 4 , [1] but there have been no reports of an experimentally observed molecule for which the inclusion of spin-orbit effects is essential for the correct identification of the ground state structure. We report here a molecular ion, [CH 2 ClI] + , for which spin-orbit interactions are crucial for the identification of the structure and vibrational frequencies of the correct ground state. Theoretically, the spin-orbit interaction is part of the relativistic effect. The importance of relativity for the description of heavy atoms is well recognized.[2] Scalar relativistic effects are routinely included in electronic-structure calculations of molecules containing heavy elements through the use of relativistic effective core potentials (RECP), but spin-orbit interactions are usually omitted when deriving optimized structures partly because of the assumption that their influence on the molecular structures is negligible and partly due to computational difficulties. Even when spin-orbit terms are available in RECPs, the usual treatment involves perturbational inclusion of these terms after the variational determination of orbitals and structures. Quantum chemical calculations employing RECPs and spinorbit operators from the start have been available for some time.[3] The spin-orbit density functional theory (DFT) method available in NWChem is particularly useful for the present purpose of demonstrating spin-orbit effects on geometries since the geometry can be optimized with both electron correlations and spin-orbit interactions included. [4] We have been investigating the reactivity of mixed dihalomethane cations for some time. Hence, we have recorded the vibrational spectra of the cations by massanalyzed threshold ionization (MATI) spectrometry.[5] Figure 1 shows the MATI spectrum of CH 2 ClI recorded by monitoring [CH 235 ClI] + in the electronic ground state. The most intense peak at around 78 644 cm À1 corresponds to the 0-0 band. The distance of each peak from the 0-0 band in this spectrum corresponds to the vibrational frequency of the cation. CH 2 ClI has nine nondegenerate normal modes: modes 1-6, with a' symmetry, and modes 7-9, with a'' symmetry. All the fundamentals and overtones of the totally symmetric modes, a', are dipole-allowed, while only the even-numbered overtones of the a'' modes are allowed. Utilizing the selection rule and the frequencies in the neutral species, [6] plausible assignments can be made for the prominent peaks; these are listed in Table 1. Modes 2 and 3 are due to CH 2 motion, modes 4 and 5 are CÀCl and CÀI stretchings, respectively, and mode 6 is IÀCÀCl bending. Other peaks in the spectrum are due to overtones and combinations.Our normal routine is to perform quantum chemical calculations for the vibrational frequencies, isotope shifts, and Franck-Condon factors to confirm, improve, or revise the phenomenological assignme...
Treatment of AlMe) and subsequent addition of ROH afford monomeric and heteroleptic (OR)AlL 2 complexes [R =
Several fluorene copolymers containing isothianaphthene units (P1, P2, and P3) or similar derivatives (P4 and P5) have been synthesized by Pd‐catalyzed Suzuki polymerization. The monomers containing isothianaphthene were prepared by a ring‐closure reaction with Lawesson's reagent. Strong photoluminescence (PL) quenching in the film state was observed for P1 and P2, which was mainly due to the enhanced quinoid character formed by introducing the isothianaphthene unit. Their energy levels of the compounds were determined using cyclic voltammetry. Among the polymers tested, the polymer containing both an isothianaphthene and a selenophene unit, P2, showed the smallest band gap of 1.85 eV. The influence of structural variation on the band gap of the polymer chains was further investigated by optimizing the geometries of several model monomers. Our results based on the optical and electrochemical properties combined with theoretical calculations showed that polymers containing isothianaphthene have small band gaps, rigid conformations, and strong tendencies to aggregation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3573–3590, 2008
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