Conjugated systems introduction

The syntheses of the dyes are presented in Figs. 3 and 4. There are three major aspects of the synthesis of fluorene-based 2PA derivatives. The first is the introduction of donor or acceptor groups into the conjugation system. The second is the construction of the conjugation backbone and the third is the... 

Functional siloles have found applications in the elaboration of silole-containing tt-conjugated systems. Because of its unique electronic properties, the introduction of a silole component or a silole cooligomer into an unsaturated chain should be a promising route to novel --electronic materials and, in this connection, the preparation of new heterocyclopentadiene monomeric precursors remains a current challenge. 

Another recent study98 does not deal with the formation of homocyclic polysilane cages, but with the insertion of oxygen into a strained bicyclic ladder polysilane. The introduction of heteroatoms into ladder polysilane skeletons seems interesting because of possible perturbations of the cr-(Si—Si) conjugation system. The oxidation of decaisopropylbicy-clo[2.2.0]hexasilane with a deficient amount of m-chloroperbenzoic acid (0.7 equivalents) affords the monooxidation products decaisopropyl-7-oxabicyclo[2.2.1]heptasilane in 32% yield and decaisopropyl-2-oxabicyclo[3.2.0]heptasilane in 18% yield (equation 27), which can be easily separated by HPLC. 

If the reaction involves a conjugated system, and if the substituent is attached directly to it and can conjugate with it, then of course there will be a direct effect on 6E or E. This can either be estimated by direct calculation of E for the whole system including the substituent or, more logically, it can be deduced from the value (AE )0 or ( l)o f°r the corresponding unsubstituted system by treating the introduction of the substituent as a perturbation and by using perturbation theory. 

The conjugate system of the C-2 nitroalkenes should posses some interesting chemical reactivity and it should be an excellent Michael reaction acceptor with reactive nucleophiles. Moreover, the steric effect of the bulky 1,6-anhydro ring should be similar to that of levoglucosenone. As a consequence, nitroalkenes are excellent precursors for the stereoselective introduction of an additional sugar moiety at C-2 with subsequent additional functional group such as nitromethylene or its reduced/acetylated analog. Moreover, this unsaturated C-2 functionality additionally fixes the conformation of the system and most importantly sterically hinders the P-D-face of both enone molecules. 

Introduction of a double bond in the acyl portion of Ar-acylenamines or A-acylanilides forms a six -electron conjugated system and therefore, an electrocyclic cyclization under photochemical conditions is expected, as in the case of photocyclization of 1,3,5-hexatrienes and stilbenes. 

It should be added that the expansion of the tr-conjugating system and/or the introduction of Se atoms with greater polarizability (as shown in BETS or TTPs) reduce the effective on-site Coulomb energy U. For example, the V values for the TTP-type donors estimated from electrochemical and optical measurements are considerably small. (TTM-TTP)l3 is a 1 1 salt with a highly one-dimensional half-filled band. Although 1 1 salts were believed to be non-metal due to the Coulomb interaction (Mott-insulator), this salt shows metallic behavior down to about 160 K. This system is regarded as a small-f/ case of a one-dimensional conductor with an inherently half-filled band [27]. 

Mercuric acetate, HgfOCOCHjjj (mp 179-182 °C), is used for dehydrogenations, resulting in the introduction of double bonds into the a positions with respect to conjugated systems [399, 400], and for the dehydrogenation of amines to imines [401, 402]. The reagent can also demethylate tertiary amines to secondary amines [403] and introduce acetoxyl groups into the a positions with respect to double bonds [404]. 

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