Electronic Properties of Vinylene-Linked Heterocyclic Conducting Polymers: Predictive Design and Rational Guidance from DFT Calculations

The band structure and electronic properties in a series of vinylene-linked heterocyclic conducting polymers are investigated using density functional theory (DFT). In order to accurately calculate electronic band gaps, we utilize hybrid functionals with fully periodic boundary conditions to understand the effect of chemical functionalization on the electronic structure of these materials. The use of predictive first-principles calculations coupled with simple chemical arguments highlights the critical role that aromaticity plays in obtaining a low band gap polymer. Contrary to some approaches which erroneously attempt to lower the band gap by increasing the aromaticity of the polymer backbone, we show that being aromatic (or quinoidal) in itself does not insure a low band gap. Rather, an iterative approach which destabilizes the ground state of the parent polymer towards the aromatic \leftrightarrow quinoidal level-crossing on the potential energy surface is a more effective way of lowering the band gap in these conjugated systems. Our results highlight the use of predictive calculations guided by rational chemical intuition for designing low band gap polymers in photovoltaic materials.Comment: Accepted by the Journal of Physical Chemistry

Phosphorus-nitrogen compounds. spiro- and crypta-phosphazene derivatives: Synthesis and spectral investigations. Structure of butane-N,N?-bis(1,4- oxybenzyl)-spiro(propane-1,3-diamino)tetrachlorocyclo-2?5, 4?5, 6?5-triphosphazatriene. Part VII

The condensation reactions between trimer, N3P 3Cl6, and diamines, 2 and 4 and {1-{N-[1-(2- hydroxynaphthylmethyl)aminomethylidene]}-2(1H)-naphthalenone, 3, yielded the new spiro-cyclic- (5 and 8) and the novel spiro-phosphazene (7) derivatives, respectively. The fully substituted phosphazene (6) was also obtained from the reaction of 5 with the excess of pyrrolidine. Compounds (4-8) have been characterized by elemental analyses, FTIR, 1H-, 13C-, 31P-NMR, HETCOR, COSY and MS. The structure of crypta-phosphazene, 8, has been examined crystallographically. Compound 8 is the first example of the crypta-phosphazene derivatives. The 31P-NMR spectra of compounds 7 and 8 indicate that, both of the compounds have anisochronism because of the stereogenic centers. The pyramidal geometry of two spiro-cyclic nitrogen atoms in compound 8, gives rise to stereogenic property. The sums of the bond angles around N4 and N5 nitrogens are 350.6(2) and 349.6(3)°, respectively. Compound 8 crystallizes in the triclinic space group P1 with a=8.798(3), b=10.498(3) and c=15.689(4)Å; ?=91.35(2), ?=103.39(4) and ?=102.88(4)°; V=1369.9(7)Å3, Z=2 and Dx=1.491gcm-3. It consists of a non-centrosymmetric, non-planar phosphazene ring with a bulky dibenzo-diazacrown etheric side group. © 2004 Elsevier B.V. All rights reserved.2001-07-05-064The authors wish to acknowledge the purchase of the CAD-4 diffractometer and financial support of this work under grants DPT/TBAG1 and CHE-93250012 of the Scientific and Technical Research Council of Turkey and Ankara University Research Fund (grant number: 2001-07-05-064) for financial support