Push-pull amino succinimidyl ester thiophene-based fluorescent dyes: synthesis and optical characterization.

The design and synthesis of new fluorescent dyes with emission range at 490-650 nm are described. Their structural and electronic properties have been characterized by both experimental techniques and quantum-chemical calculations. The chromophores are donor-π-bridge-acceptor push-pull compounds with a π bridge of phenyl and thiophene rings and their combination.

Silyloxyazadienes: one intermediate and two competitive pericyclic reactions.

The two competing mechanisms in the reaction of 3-trialkylsilyloxy-2-aza-1,3 dienes to form beta-lactams through a [2+2] electrocyclic ring closure or tetrahydrooxazinan-4-ones via a [4+2] hetero-Diels-Alder reaction were studied using Density Functional computations. Although the [2+2] and [4+2] mechanisms are typical of dienes, their competition, starting from the same diene intermediate, has not yet been observed and analyzed. This competition is governed by a delicate interplay between temperature and substituents at the diene and dienophile, respectively.

Alkylenesulfanyl-bridged bithienyl cores for simultaneous tuning of electronic, filming, and thermal properties of oligothiophenes.

DPY and DPE alkylenesulfanyl-bridged bithienyls were prepared by a highly effective ring-closing reaction via arylalkylsulfonium intermediate and used as inner cores in oligothiophenes. HOMO-LUMO energy levels, conformational flexibility, and intrinsic asymmetry of the cores are reflected in the electronic, film-forming, and thermal properties of the corresponding oligomers.

Polyvinyl-locked versus free quaterthiophene: effect of spatial constraints on the electronic properties of n-hexylquaterthiophene.

A soluble, low-weight fraction of poly(alpha-vinyl,omega-n-hexyl-quaterthiophene), PT4Hex, having n-hexylquaterthiophenes as side-chain groups, is prepared by free-radical polymerization of alpha-vinyl,omega-n-hexyl-quaterthiophene and the corresponding properties compared to those of free di-n-hexylquaterthiophene (T4Hex). Optical analysis (absorption and emission) and X-ray diffraction data indicate that in the polyvinyl-locked architecture the quaterthiophene pendants adopt a cofacial arrangement with a mutual distance close enough for pi-pi orbitals to overlap ( approximately 4 A). As a consequence of the close chain packing, a shift of the reduction potential of about 0.

Synthesis, multiphase characterization, and helicity control in chiral DACH-linked oligothiophenes.

A new class of chiral oligothiophenes is described. Mono-, bi-, ter-, and quarterthiophenes have been linked to enantiopure trans-1,2-cyclohexanediamine (DACH) via diamino or diimino moieties. The stereochemistry of DACH, the type of linker, and oligothiophene size determine the conformational flexibility of these molecules and consequently their molecular and supramolecular helicity in solution and in the solid state.

Regioselective Oligomerization of 3-(Alkylsulfanyl)thiophenes with Ferric Chloride.

The action of FeCl(3) on 3-(alkylsulfanyl)thiophenes (3-(alkylthio)thiophenes) leads to the one-step formation of regioregular alpha-conjugated oligothiophenes, from trimer to octamer, depending on the solvent used and on the length of the alkyl chain. The regiochemistry of these oligomers is characterized by one inner head-to-head linkage between adjacent rings and by a variable number of lateral head-to-tail junctions. The reaction of ferric chloride with the head-to-head and head-to-tail bis(methylsulfanyl)-2,2'-bithiophenes gives the corresponding tetramers, while the reaction with the tail-to-tail counterpart affords a high molecular weight insoluble material.