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Nontemplated approach to tuning the spectral properties of cyanine-based fluorescent nanoGUMBOS.

ABSTRACT: Template-free controlled aggregation and spectral properties in fluorescent organic nanoparticles (FONs) is highly desirable for various applications. Herein, we report a nontemplated method for controlling the aggregation in near-infrared (NIR) cyanine-based nanoparticles derived from a group of uniform materials based on organic salts (GUMBOS). Cationic heptamethine cyanine dye 1,1',3,3,3',3'-hexamethylindotricarbocyanine (HMT) was coupled with five different anions, viz., [NTf(2)(-)], [BETI(-)], [TFPB(-)], [AOT(-)], and [TFP4B(-)], by an ion-exchange method to obtain the respective GUMBOS. The nanoGUMBOS obtained via a reprecipitation method were primarily amorphous and spherical (30-100 nm) as suggested by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). The formation of tunable self-assemblies within the nanoGUMBOS was characterized using absorption and fluorescence spectroscopy in conjunction with molecular dynamics simulations. Counterion-controlled spectral properties observed in the nanoGUMBOS were attributed to variations in J/H ratios with different anions. Association with the [AOT(-)] anion afforded predominant J aggregation enabling the highest fluorescence intensity, whereas [TFP4B(-)] disabled the fluorescence due to predominant H aggregation in the nanoparticles. Analyses of the stacking angle of the cations based on molecular dynamic simulation results in [HMT][NTf(2)], [HMT][BETI], and [HMT][AOT] dispersed in water and a visual analysis of the representative simulation snapshots also imply that the type of aggregation was controlled through the counterion associated with the dye cation.

SUBMITTER: Das S

PROVIDER: S-EPMC2917973 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Nontemplated approach to tuning the spectral properties of cyanine-based fluorescent nanoGUMBOS.

Das Susmita S Bwambok David D El-Zahab Bilal B Monk Joshua J de Rooy Sergio L SL Challa Santhosh S Li Min M Hung Francisco R FR Baker Gary A GA Warner Isiah M IM

Langmuir : the ACS journal of surfaces and colloids 20100801 15

Template-free controlled aggregation and spectral properties in fluorescent organic nanoparticles (FONs) is highly desirable for various applications. Herein, we report a nontemplated method for controlling the aggregation in near-infrared (NIR) cyanine-based nanoparticles derived from a group of uniform materials based on organic salts (GUMBOS). Cationic heptamethine cyanine dye 1,1',3,3,3',3'-hexamethylindotricarbocyanine (HMT) was coupled with five different anions, viz., [NTf(2)(-)], [BETI(- ...[more]

PMID: 20583774

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Project description:In the present study, the influence of the hydrogen bonding for the one- and two-photon absorption of the prototypical squaraine dye is investigated with quantum chemistry tools. The central squaraine unit is bound by strong hydrogen bonds with 4-substituted N,N'-diphenylurea and, alternatively, N,N'-diphenylthiourea molecules, which affects to a high extend the properties of the squaraine electron accepting moiety, thus shifting its maximum absorption wavelength and enhancing the TPA cross section. The replacement of oxygen by sulfur atoms in the squaraine central ring, known to affect its photophysical behavior, is considered here as the way of modifying the strength and nature of the intermolecular contacts. Additionally, the influence of the oxygen-by-sulfur replacement is also considered in the N,N'-diphenylurea moiety, as the factor affecting the acidity of the N-H protons. The introduction of the sequence of the substituents of varying electron-donating or electron-withdrawing characters in the position 4 of N,N'-diphenyl(thio)urea subsystems allows to finely tune the hydrogen bonding with the central squaraine unit by further modification of the N-H bond characteristics. All of these structural modifications lead to the controlled adjustment of the electron density distribution, and thus, the properties affected such as transition moments and absorption intensity. Ab initio calculations provide strong support for this way of tailoring of one- or two-photon absorption due to the obtained strong hypsochromic shift of the maximum one-photon absorption wavelength observed particularly for thiosquaraine complexes and an increase in the TPA wavelength together with the increase in the TPA cross section. Moreover, the source of the strong modification of the thiosquaraine OPA in contrast to the pristine oxosquaraine upon N,N'-diphenyl(thio)urea substitution is determined. Furthermore, for the first time, the linear dependence of the non-additivity in the interaction energy on the Hammett substituent constant is reported. The stronger the electron-donating character of the substituent, the larger the three-body non-additive components and the larger their percentage to the total interaction energy.

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Nontemplated approach to tuning the spectral properties of cyanine-based fluorescent nanoGUMBOS.

Publications

Nontemplated approach to tuning the spectral properties of cyanine-based fluorescent nanoGUMBOS.

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