- Tuning the Optoelectronic Properties of Stannoles by the Judicious Choice of the Organic Substituents
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Stannoles are organometallic rings in which the heteroatom is involved in a form of conjugation that is called σ?-π? conjugation. Only very little is known about how the substituents on the Sn atom or substituents on the stannole ring determine the optoelectronic properties of these heterocycles. In this work, this question has been studied experimentally and theoretically. Calculations of optimized equilibrium geometries, energy gaps between the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs), and of the absorption spectra of a wide range of compounds were performed. The computational data showed that the substituents on the Sn atom influence the optoelectronic properties to a lower extent than the substituents in the 2 and 5 positions of the ring. These substituents in the 2 and 5 positions of the stannole ring can also have a strong influence on the overall planarity of the structure, in which mesomeric effects can play a substantial role only if the structure is planar. Thus, only structures with a planar backbone are of interest in the context of tuning the optoelectronic properties. These were selected for the experimental studies. On the basis of this information, a series of six novel stannoles was synthesized by the formation of a zirconium intermediate and subsequent transmetalation to obtain the tin compound. The calculated electronic HOMO-LUMO energy gaps varied between 2.94 and 2.68 eV. The measured absorption maxima were located between 415 and 448 nm compared to theoretically calculated values ranging from 447 nm (2.77 eV) to 482 nm (2.57 eV). In addition to these optical measurements, cyclic voltammetry data could be obtained, which show two reversible oxidation processes for three of the six stannoles. With this study, it could be demonstrated how the judicious choice of the substituents can lead to large and predictable bathochromic shifts in the absorption spectra.
- Ramirez Y Medina, Isabel-Maria,Rohdenburg, Markus,Mostaghimi, Farzin,Grabowsky, Simon,Swiderek, Petra,Beckmann, Jens,Hoffmann, Jonas,Dorcet, Vincent,Hissler, Muriel,Staubitz, Anne
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supporting information
p. 12562 - 12575
(2018/10/20)
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- push-push and push-pull polystannanes
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The synthesis and characterization of polystannanes with push or pull moieties attached to the tin backbone are described. Precursor tetra aryl- (1, 2) stannanes were converted to mono- (3) and dichloro- (4, 5) stannanes by either sequential chlorination or by redistribution reactions with SnCl4. Compounds 4 and 5 were transformed to polymerisable tin dihydride monomers 6 and 7 using a large excess (10×) of NaBH4. Homopolymer 8 with electron donating aryl substituents (p-MeOC6H4-) was synthesized by dehydrogenative polymerization using Wilkinson's catalyst. Attempts to prepare the homopolymer 9 with electron withdrawing aryl substituents (p-CF3C6H4-) from the dehydrocoupling of 7 using similar conditions led only to the formation of low molecular weight oligomeric species. Two alternating polymers, 10 and 11, were synthesized by condensation polymerization of (n-Bu)2Sn(NEt2)2 with monomers 6 or 7. The first was a push-push alternating polymer, 10, comprised of a repeating unit consisting of two different electron donating groups (p-MeOC6H4-, n-Bu) at neighboring tin centres. The second was a push-pull alternating polymer, 11, bearing both an electron donating group (n-Bu) and a strongly electron withdrawing substituent (p-CF3C6H4-) at neighboring tin atoms. All small molecule stannanes and tin-containing polymers were characterized by NMR (1H, 13C, 119Sn, and where required 19F) spectroscopy, MS or EA. The absolute molecular weights of tin polymers (8, 10, 11) were determined by triple detection GPC and in the range of 1.07 × 104 to 1.95 × 104 Da. Rapid photodegradation of polymers was observed by UV-Vis spectroscopy, with a slower degradation observed for the push-pull polymer, 11, compared to the push-push polymer, 10.
- Dhindsa,Jacobs,Lough,Foucher
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p. 14094 - 14100
(2018/10/20)
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