Semiconductors, intrinsic molecular

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

The phthalocyanine radical complex of lithium (PcLi ) is a member of the class of intrinsic molecular semiconductors [27]. Its preparation is carried out by electrosynthesis at 70°C under... 

Guillaud, G. et ah. Field-effect transistors based on intrinsic molecular semiconductors, Chem. Phys. Lett., 167, 503, 1990. 

The only class of lanthanidomesogens for which electrical properties have been investigated in detail, are the bis(phthalocyaninato)lanthanide(III) sandwich complexes. As already described in Section 8, the free electron in these complexes is associated with the extensive re-system of the phthalocyanine macrocycles. The individual Pc2Lu units can be considered nominally as Lu " Pc2 The bis(phthalocyaninato)lutetium(III) complexes are intrinsic molecular semiconductors. The generation of charge carriers can be represented by the reaction AAA A free carriers, where A is the molecular unit. The ionized pair A " A is photochemically or thermally activated. 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

From 3 to (say) 0.3 MPM the conductivity is not in the metallic range, but we believe that the material behaves like an intrinsic semiconductor, current being carried by electrons in the upper band. This, as we have seen, is not a Hubbard band, but the band formed from molecular orbitals for an extra electron on molecular dimers. In this range d In a jdT... 

In order to understand this process, the nature of the Fermi level must be considered. Within the nomenclature of physics, the Fermi level is defined as the energy at which there is a 50% probability of finding an electron in a metal— what a chemist would call the highest filled molecular orbital (i.e., the top of the valence band). In an intrinsic semiconductor, a material having a completely filled valence band and a completely empty conduction band, this energy level... 

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