Resonance Raman spectra of hydroxyphenyl squaraines: acid–base <i>versus</i> aggregation equilibria

Lopes, José Guilherme S.; Farani, Régis A.; Oliveira, Luiz Fernando Cappa de; Santos, Paulo S.

doi:10.1002/jrs.1448

Cited by 10 publications

(9 citation statements)

References 19 publications

(15 reference statements)

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“…When the water content is almost 50% in the solvent then the band blue shifts in this case also. This clearly suggests, here 7 and 10 undergo acid base equilibrium and not aggregation. , …”

Section: Resultsmentioning

confidence: 83%

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Third Order Nonlinear Optical Properties of Squaraine Dyes Having Absorption below 500 nm: A Combined Experimental and Theoretical Investigation of Closed Shell Oxyallyl Derivatives

et al. 2010

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Nonlinear optical (NLO) activity of a molecule in general is connected to fundamental issues like charge transfer, conjugation, polarization, and recently suggested and less investigated diradical character. Extensively studied molecules for negative second order hyperpolarizabilities are the centrosymmetric squaraine derivatives (SQ) which have absorption in the region greater than 600 nm. These have no formal electronic structure but can be represented as a mixture of zwitterionic and diradicaloid valence bond resonance structures. In this work we have designed and synthesized arylamino SQ, 1−10, which bias the valence bond resonance picture completely to the zwitterionic type and totally eliminates the diradicaloid contribution (estimated using computational studies to be zero). Due to this, the lowest energy transitions are blue-shifted to the region less than 500 nm. We have carried out degenerate four wave mixing (DFWM) studies for estimation of γ values of these molecules using a 800 nm wavelength laser. The γ values are measured under nonresonant conditions and also at intensities where two photon absorption does not play any role. Nonlinear absorption properties of these molecules are studied through Z scan technique. The γ values, though smaller than the SQ having absorption in the red region, are reasonably large and range from −1.2 to −6.9 × 10−33 esu. High level computational techniques and model molecules have been utilized to understand the transition and the NLO activity in these molecules.

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“…When the water content is almost 50% in the solvent then the band blue shifts in this case also. This clearly suggests, here 7 and 10 undergo acid base equilibrium and not aggregation. , …”

Section: Resultsmentioning

confidence: 83%

“…In the literature such a double peak has been assigned to aggregation/or water induced aggregation . Some other recent studies have shown that in some cases it could also arise due to traces of water present in the organic solvent interacting with the dye which leads to acid−base equilibrium and not aggregation. , …”

Section: Resultsmentioning

confidence: 99%

Third Order Nonlinear Optical Properties of Squaraine Dyes Having Absorption below 500 nm: A Combined Experimental and Theoretical Investigation of Closed Shell Oxyallyl Derivatives

et al. 2010

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“…23 This aggregation is dependent on solvent type, concentration, and pH. 53 For example, the solvent polarity affects the zwitterionic structure, resulting in polarization of the squaraines, forming unusual aggregation structures. The dimer aggregates formed are classified as either J-type or H-type aggregates.…”

Section: Optical Propertiesmentioning

confidence: 99%

Squaraine dyes in molecular recognition and self-assembly

2009

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Squaraine dye molecules and their derivatives are gaining significant interest in the field of supramolecular chemistry, both in host-guest recognition and self-assembly. The unique structure and properties of squaraine molecules has led to extensive research into their use as sensors. This feature article covers the most recent studies (2004-2009) in the development, characterization, and application of squaraine dye-based molecular sensors, self-assembly, and their use in polymeric materials and biological applications.

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“…Atenta-se ao fato de que este composto não apresenta átomos de nitrogênio no ligante, reafirmando que não existe na literatura um consenso acerca do conceito de esquaraínas. 57 São geralmente preparados pela condensação de compostos aromá-ticos ou heteroaromáticos ricos em elétrons como N,N-dialquilanilinas, benzotiois, fenois, azulenos e pirrois com ácido esquárico. Assim, um enorme número de sistemas tem sido sintetizado com a variação do sistema doador, havendo várias possibilidades para design de uma infinidade de esquaraínas com características particulares.…”

Section: Esquaraínasunclassified

Oxocarbonos, pseudo-oxocarbonos e esquaraínas

Oliveira¹,

Diniz²,

Oliveira³

2009

Quím. Nova

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Recebido em 19/11/08; aceito em 27/3/09; publicado na web em 26/8/09 OXOCARBONS, PSEUDO-OXOCARBONS AND SQUARAINES. Oxocarbons ions are cyclic compounds presenting unusual electronic and vibrational properties. These molecules anions possess a high symmetry and degree of electronic delocalization, characteristics that have been discussed in several structural and spectroscopic investigations. Compounds in which one or more of the carbonyl oxygen atoms are replaced by other atoms or groups are called pseudo-oxocarbons. Compounds formed by substitution of the carbonyl groups by nitrogen groups former a new class named squaraines. Specificity the dicyanomethylene groups are interesting because of the possibility of further extension of the electronic delocalization and a new coordination site. These molecules also present interesting coordination properties which make these systems potentially useful in crystal engineering research.Keywords: oxocarbons; pseudo-oxocarbons; squaraines. INTRODUÇÃOOxocarbonos são compostos orgânicos formados essencialmente por carbono e oxigênio, apresentam-se como diácidos em sua forma neutra e seus ânions possuem fórmula geral C n O n 2-onde n varia de 3 a 6. Os ânions croconato (n=5) e rodizonato (n=6) Os oxocarbonos apresentam características particulares muito interessantes, tais como, estruturas cíclicas planares, elevada simetria molecular, sistemas π-deslocalizados e espectros eletrônicos singulares por apresentarem o efeito Jahn-Teller. 4 Uma evidência experimental acerca da estrutura de ressonância destes compostos foi obtida por Hirata e colaboradores através da espectroscopia de absorção no infravermelho.5 Nestes estudos foi verificada a ausência da banda referente ao ν(CO) que ocorre na região ~1850-1710 cm -1. Em estudos posteriores constatou-se que a variação do tamanho do anel promove uma interessante modificação na deslocalização eletrônica do respectivo oxocarbono: quanto maior o anel menor a deslocalização eletrônica. 5Deste ponto de vista , o íon deltato é o único oxocarbono considerado realmente aromático apresentando uma maior estabilidade, devida à maior distribuição de carga, quando comparado aos demais oxocarbonos, e esta estabilidade diminui com o aumento do tamanho do anel. Os demais oxocarbonos são considerados, formalmente, não-aromáticos, porém, apresentando a elevada conjugação eletrônica característica.Estas espécies apresentam elevado valor de constante de dissociação, evidenciando a elevada estabilidade conseguida através da ressonância de seus respectivos ânions. Por exemplo, os valores de pK 1 e pK 2 para o íon croconato são 0,8 e 2,2, respectivamente, para o íon esquarato são 0,5 e 3,5 e para o rodizonato são 4,3 e 4,7, respectivamente. 6A elevada simetria molecular é verificada através de seus espectros eletrônicos, onde o perfil espectroscópico evidencia a presença do efeito Jahn-Teller característico destas espécies (Figura 2). O dupleto observado ocorre devido à dupla degenerescência do primeiro estado eletrônico excitado presente nestas molécul...

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Resonance Raman spectra of hydroxyphenyl squaraines: acid–base versus aggregation equilibria

Cited by 10 publications

References 19 publications

Third Order Nonlinear Optical Properties of Squaraine Dyes Having Absorption below 500 nm: A Combined Experimental and Theoretical Investigation of Closed Shell Oxyallyl Derivatives

Third Order Nonlinear Optical Properties of Squaraine Dyes Having Absorption below 500 nm: A Combined Experimental and Theoretical Investigation of Closed Shell Oxyallyl Derivatives

Squaraine dyes in molecular recognition and self-assembly

Oxocarbonos, pseudo-oxocarbonos e esquaraínas

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