PM3 geometry optimization and CNDO/S-CI computation of UV/Vis spectra of large organic structures: Program description and application to poly(triacetylene) hexamer and taxotere
✍ Scribed by Baumann, Harold; Martin, Rainer E.; Diederich, Fran�ois
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 542 KB
- Volume
- 20
- Category
- Article
- ISSN
- 0192-8651
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✦ Synopsis
SIXW.C, a new C version of the computer program CNDUV99
Ž . based on CNDOrS-CI with inclusion of doubly excited configurations is described and shown to be useful for the computation of the UVrVis spectra of fairly large molecules. The geometries of the molecules were obtained by our C version of program PM3. To demonstrate the broad applicability of program SIXW.C we have chosen two representative examples: first, a linearly conjugated oligomer of defined length; and, second, a natural product that currently plays a very significant role in cancer therapy. The first molecule is a recently synthesized linearly conjugated monodisperse hexamer of ;4.6 nm in length Ž . Ž . C H O Si , with poly triacetylene backbone. Despite the 36 conjugated 126 222 12 14 C-atoms of the framework, it exhibits remarkable thermal and environmental stability, which allows in-depth investigation of its physical properties. Therefore, this made it a very attractive candidate for comparison of the theoretically calculated and experimentally measured UVrVis spectra, as there is still considerable interest in predicting linear optical properties of large conjugated organic molecules at the border to polymers. The agreement between experimental and calculated spectra is better with the UHF-PM3-rather than with the RHF-PM3-optimized structure of the molecule, showing, for the former, excellent agreement between the experimental and theoretical longest Ž . Ž y1 . wavelength maximum , which differ by only 16 nm 802 cm .