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2.
Chem Commun (Camb) ; (23): 2378-80, 2007 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-17844752

RESUMO

Using the bidirectional NICS scan method in conjunction with two-photon absorption (TPA) measurements, it has proved possible to determine the relationship between pi-conjugation and aromaticity in two structurally related expanded porphyrin systems, sapphyrin and inverted sapphyrin, and establish that differences in these defining factors depend on the presence or absence of a key sp3 hybrid molecular orbital within the macrocyclic periphery.


Assuntos
Porfirinas/química , Análise Espectral/métodos
5.
Chem Commun (Camb) ; (24): 2479-81, 2007 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-17563802

RESUMO

Intramolecular charge transfer in 5,15-bis(azulenylethynyl) substituted zinc(ii) porphyrin leads to a significant enhancement of two-photon absorption at near-IR region, which has been investigated by femtosecond Z-scan method.


Assuntos
Alcinos/química , Azulenos/química , Metaloporfirinas/química , Estrutura Molecular , Fótons , Espectroscopia de Luz Próxima ao Infravermelho
7.
J Am Chem Soc ; 128(43): 14128-34, 2006 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-17061896

RESUMO

A strong correlation among calculated Nucleus-Independent Chemical Shift (NICS) values, molecular planarity, and the observed two-photon absorption (TPA) values was found for a series of closely matched expanded porphyrins. The expanded porphyrins in question consisted of [26]hexaphyrin, [28]hexaphyrin, rubyrin, amethyrin, cyclo[6]pyrrole, cyclo[7]pyrrole, and cyclo[8]pyrrole containing 22, 24, 26, 28, and 30 pi-electrons. Two of the systems, [28]hexaphyrin and amethyrin, were considered to be antiaromatic as judged from a simple application of Hückel's [4n + 2] rule. These systems displayed positive NICS(0) values (+43.5 and +17.1 ppm, respectively) and gave rise to TPA values of 2600 and 3100 GM, respectively. By contrast, a set of congeners containing 22, 26, and 30 pi-electrons (cyclo[n]pyrrole, n = 6, 7, and 8, respectively) were characterized by a linear correlation between the NICS and TPA values. In the case of the oligopyrrolic macrocycles containing 26 pi-electron systems, a further correlation between the molecular structure and various markers associated with aromaticity was seen. In particular, a decrease in the excited state lifetimes and an increase in the TPA values were seen as the flexibility of the systems increased. Based on the findings presented here, it is proposed that various readily measurable optical properties, including the two-photon absorption cross-section, can provide a quantitative experimental measure of aromaticity in macrocyclic pi-conjugated systems.


Assuntos
Porfirinas/química , Estrutura Molecular , Óptica e Fotônica , Fótons , Espectrometria de Fluorescência , Espectroscopia de Luz Próxima ao Infravermelho
8.
Org Lett ; 8(18): 4141-4, 2006 Aug 31.
Artigo em Inglês | MEDLINE | ID: mdl-16928094

RESUMO

Highly efficient synthesis of meso,meso-dibromo doubly and triply fused diporphyrins has been achieved through a powerful oxidative coupling mediated by AuCl3-AgOTf combination. In addition, palladium-catalyzed debromination of meso-bromoporphyrins has been developed. This debromination protocol enables employment of bromine as a protecting group for the reactive meso-position of porphyrins.


Assuntos
Ouro/química , Porfirinas/síntese química , Bromo/química , Estrutura Molecular , Oxirredução
10.
J Am Chem Soc ; 128(5): 1700-4, 2006 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-16448144

RESUMO

Recently, covalently linked or self-assembled porphyrin array systems have attracted much attention for their enhanced two-photon absorption (TPA) behaviors. In this study, we have investigated the TPA properties of various dihedral angle controlled, directly linked porphyrin dimers and arrays to elucidate the relationship between the pi-conjugation pathway and TPA properties. We have demonstrated a strong correlation between pi-conjugation (aromaticity) and TPA properties in porphyrin assemblies.

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