ABSTRACT
As an example of molecular design of new polymers, structures and properties of poly(ethylene thionoterephthalate) (PET[S2]) and the related polymers have been predicted from calculations of ab initio molecular orbital (MO) theory, rotational isomeric state (RIS) scheme, and periodic density functional theory (DFT). The MO calculations were confirmed by NMR experiments and introduced to the RIS scheme for PET[S2] to yield its configurational properties, which are compared herein with those of analogous polyester, polythioester, and polydithioester. Configurational properties of randomly thiono-substituted poly(ethylene terephthalate) (PET), PET[S z O1-z ], were also evaluated as a function of sulfidity (z). On the assumption that the crystal of PET[S2] can be expressed as an isomorphic replacement of the PET crystal, the crystal structure was optimized by a periodic DFT simulation and its Young's moduli in the a-, b-, and c-axis directions were, respectively, evaluated to be Ea = 0.94(7.20) GPa, E b = 19.58(22.26) GPa, and E c = 142.1(182.4) GPa, where the parenthetic values are those of the PET crystal. There is a possibility that properties of PET[S z O1-z ] will be controlled between those of PET and PET[S2] by adjusting the sulfidity. The potential practical applications of the polythionoesters are also discussed herein. By purely theoretical computations, the structures and properties of the not-yet synthesized polymers were predicted quantitatively; that is, the theoretical molecular design of new polymers has been achieved.
ABSTRACT
Eu3+ and Tb3+ ions were site-selectively doped into LaLuO3 with the orthorhombic perovskite-type structure (ABO3), and their luminescence properties were examined considering the doping sites (A or B sites). The X-ray diffraction analysis revealed the expansion or contraction of the unit cell volumes of the materials depending on the doping sites. The spectra of X-ray absorption near edge structure for the Eu and Tb LIII edge exhibited different shapes for the ions at A and B sites, confirming the site-selective doping of Eu3+ and Tb3+ in LaLuO3. The photoluminescence (PL) and PL excitation (PLE) spectra of the materials also showed some differences caused by the doping sites. The intensities of the Eu3+ PL peaks derived from the 5D0-7F1 transitions and those from the 5D0-7F2 transitions were markedly different between Eu3+ at A sites and those at B sites because of the different site symmetries. The splitting of the intense Tb3+ PL peaks originating from the 5D4-7F5 transitions and the absence of PL peaks from 5D3-7FJ transitions were found only for Tb3+ at B sites because of the strong crystal field at B sites. In addition to the PL spectra, the positions of PLE peaks originating from charge transfer transitions in Eu3+ and the 4f-5d transitions in Tb3+ depended on the doping sites. The successful site-selective doping enabled us to clarify the site-sensitive luminescence properties of Eu3+ and Tb3+ doped in the perovskite-type LaLuO3.
ABSTRACT
The title compounds, C16H14O2S2 and C16H14O3S, which are monomeric models (models D and E) for a polythio-noester and a poly(ester-co-thio-noester), respectively, crystallize in the space group P21/c and are isostructural with each other. The mol-ecule in each crystal is located on an inversion centre and has an all-trans structure. The asymmetric unit comprises one half-mol-ecule. In the crystal, there are inter-molecular Câ¯S contacts [3.391â (3) and 3.308â (3)â Å for models D and E, respectively] and C-Hâ¯π inter-actions, which form a layer structure parallel to the bc plane. The carbonyl and thio-carbonyl groups of the model E compound are each disordered over two equivalent sites about the inversion centre with equal occupancies.