Effect of the group IV elements on the Π anion and cation states of thiophene and furan determined by means of ETS and UPS |
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Authors: | Alberto Modelli Giuseppe Distefano Derek Jones Giancarlo Seconi |
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Institution: | Istituto Chimico G. Ciamician, Università di Bologna, Via F. Selmi 2, 40126 Bologna Italy;Istituto dei Composti del Carbonio Contenenti Eteroatomi e Loro Applicazioni del C.N.R., Via Tolara di Sotto 89, 40064 Ozzano Emilia, Bologna Italy |
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Abstract: | The electron-transmission and He(I) photoelectron spectra of Si(CH3)3, Sn(CH3)3 and CH2Si(CH3)3 derivatives of thiophene and furan have been recorded. The first two substituents perturb the energies of the outer filled π orbitals and of the empty π* orbitals in opposite directions, causing a reduction of the HOMO/LUMO energy separation. The stabilization experienced by the π* MO's depends on their wavefunction coefficients at the site of substitution, and is attributed to interaction with low-lying empty orbitals of the substituent groups. The relatively small size (~ 0.4 eV) of this effect on the unoccupied ring MO's suggests that it should not appreciably affect the energy of the filled MO's.The strong conjugation between the π* unoccupied orbital of the nitro group and those of thiophene has also been investigated. |
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