Thiophenes electronic structure

The similarity of the electronic structures of thiophene and tellurophene [72JCS (Pl)199] implies that their chemistry toward Fc3(CO)l2 should be the same. Thus, tellurophene produces [Fe3Fc2(CO)9], ferrole 83, and 114 [72JOM(42)C87,96JCS (D)1545]. The same trend is observed in the reactions of the derivatives of tellurium and selenium heterocycles [97JCS(D)1579, 98JCS(D)3947]. 

Figure 9.11 Thiophene adsorbed at 500 K on an H-atom pretreated MoS2 cluster (50 x 54 A2). Beam-like features at the metallic edge [scan line (i)] and the shifted intensity of the outermost edge protrusions relative to the clean edge (triangles refer to the clean edge). These shifts in intensity [line scan (ii)] are associated with changes in the local electronic structure after adsorption of thiophene observed with STM. All the images were taken at room temperature subsequent to thiophene adsorption at 500 K. (Reproduced from Ref. 34).

The electronic structures of furan, thiophene, and selenophene, their protonated complexes, and their anions have been calculated by the extended Hiickel method.6 The results of these calculations have been used to determine the influence of the heteroatom on the degree of aromaticity and electron density. 

Cp-Cp bond (1.419(14) A) while the former become longer than the latter in the rings closer to the center of the molecule. This indicates that the electronic structure of the terminal rings is closer to that of neutral thiophene, while the quinoidal character becomes greater in the rings closer to the central position. 

Dannetun P, Boman M, Stafstrom S, Salaneck WR, Lazzaroni R, Fredriksson C, Bredas JL, Zamboni R, Taliani C (1993) The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors. J Chem Phys 99(l) 664-672 Ahn H, Whitten JE (2003) Vapor-deposition of aluminum on thiophene-terminated self-assembled monolayers on gold. J Phys Chem B 107(27) 6565-6572 Fisher GL, Flooper A, Opila RL, Jung DR, Allara DL, Winograd N (1999) The interaction between vapor-deposited A1 atoms and methylester-terminated self-assembled monolayers studied by time-of-flight secondary ion mass spectrometry, X-ray photoelectron spectroscopy and infrared reflectance spectroscopy. J Electron Spectrosc Relat Phenom 98-99 139-148... 

Theoretical calculations using the semiempirical CNDO/2 method including d- orbital participation in (Id X = O, NH, S Y = S) predicted singlet ground states for these systems as well as substantial n- bond character between the S—C bonds arising from dir-pTr overlap, and very little double bond character in the central C—C bond (74JA1817). There is also considerable contribution to the electronic structure from dipolar canonical forms in (Id X = O, NH Y = S) compared to thieno[3,4-c]thiophene (9) as evidenced by the respective calculated dipole moments of 0.15 and 3.21 D for the former and 0.00 D for the latter. 

The solvent perturbation technique has been used to study the absorption bands attributable to singlet-triplet transitions in benzo-[6]thiophene, using ethyl iodide as the perturbing solvent.173 Attempts to obtain information on the -electron conjugation in the 5-membered ring of benzo[6]thiophene by examination of the vibrational structure of the electronic spectrum were unsuccessful.171 UV evidence suggests that the valence shell of the sulfur atom can expand to a 10-electron structure in benzo[6]thiophene.156... 

The optical nonlinearity is strongly dependent on the extent of ir-electron delocalization from one repeat unit to another in the polymer (or oligomer) structure. This effective delocalization is not always equally manifested but depends on the details of repeat unit electronic structure and order. For example, in a sequentially built structure, the ir-delocalization effect on Y is found to be more effective for the thiophene oligomers than it is for the benzene oligomers (5). 

The comparison between predicted and experimental spectra allows a validation of the methods and provides suggestions for the interpretation of the relevant phenomena in terms of changes of the molecular electronic structure and equilibrium geometry. In particular, the study carried out on thiophene dimers clearly points out the relevant role of 77-77 interactions occurring in the stacks of molecules characteristic of the solid crystalline phases. The fundamental importance of this kind of interaction has been recently demonstrated by studies [35] dealing with the charge transport properties of new conjugated molecular materials suitably synthesized for application in the field of molecular electronics [36],... 

The basis and extent of their aromaticity is discussed in Chapter 1. In summary, the capacity for the lone pair on a particular heteroatom to be delocalised is inversely related to the electronegativity of the heteroatom. For instance, furan is the least aromatic of the trio because oxygen has the greatest electronegativity and hence mesomeric representations 2.4b-e make relatively less of a contribution to the electronic structure of furan than they do in the cases of pyrrole and thiophene. The order of aromaticity is furan < pyrrole < thiophene. We shall see later how this variation in aromaticity affects the reactivities of these three related heterocycles. 

In the reduced state, poly-3-methyl thiophene is an intrinsic semiconductor with an energy gap of 1.95 eV. (a) What would be the value in electron volts of its Fermi level (b) Show that the concentration of electrons in the conduction band would be negligible. However, from 0.45 to 1.1V on the normal hydrogen scale, this polymer shows metallic conductivity, (c) What change in electronic structure has occurred ... 

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