title: 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.
authors.affiliation: Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: Susmita
authors.initials: S
authors.lastname: Das
authors.forename: David
authors.initials: D
authors.lastname: Bwambok
authors.forename: Bilal
authors.initials: B
authors.lastname: El-Zahab
authors.forename: Joshua
authors.initials: J
authors.lastname: Monk
authors.forename: Sergio L
authors.initials: SL
authors.lastname: de Rooy
authors.forename: Santhosh
authors.initials: S
authors.lastname: Challa
authors.forename: Min
authors.initials: M
authors.lastname: Li
authors.forename: Francisco R
authors.initials: FR
authors.lastname: Hung
authors.forename: Gary A
authors.initials: GA
authors.lastname: Baker
authors.forename: Isiah M
authors.initials: IM
authors.lastname: Warner
mesh_terms: D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D053758:Nanoparticles / Q000737:chemistry*; D036103:Nanotechnology; D019265:Spectroscopy, Near-Infrared