Scanning electron microscopy image and Raman micromapping of tightly bound agglomerates of gold nanostars and J-aggregates of JC1 dye are given in the left and the right insets, respectively. The formation of the hybrid structures of two constituent compounds has been further confirmed by surface-enhanced Raman scattering (SERS) measurements using a confocal Raman microscopy setup (Alpha300, 600 mm−1 grating, 3 cm−1 spectral resolution, continuous wave laser excitation at 532 nm, WITec, Ulm, Germany), as the hot spots provided by sharp tips of agglomerated Au nanostars are expected to enhance Raman scattering response of the attached organic compounds . Indeed, the SERS spectrum
of the hybrid nanostructures of gold nanostars and the JC1 J-aggregates (red curve in Figure 3) AZD8931 shows identical but by more than an order of magnitude enhanced features as compared to the conventional Raman spectrum of J-aggregates (black
curve in Figure 3). SC79 mw Raman micromapping of hybrid gold nanostars/J-aggregate (JC1) complexes dispersed over a glass slide (Figure 3, right inset) directly demonstrates the strong enhancement of the Raman signal at the location of agglomerates. Results and discussion The absorption spectrum of Au nanostars exhibits a broad, intense band centered at 623 nm, along with a less intense shoulder at 827 nm (Figure 4a, black curve). J-aggregates of JC1 show a narrow absorption band (J-band) at 595 nm with a full width at half maximum of 7 nm, alongside
with a broader absorption band, positioned at the lower wavelength side from the J-band (at 500 nm) which we assign to the absorption of JC1 see more monomers (Figure 4c) . JC1 dye has extremely poor water solubility, which favors the formation of J-aggregates even at 0.1 μM concentration. For this reason, the peak associated with J-aggregates is always present in the spectra of aqueous solution of JC1, which makes it difficult to measure the absorption spectrum of the dye monomers alone . To ensure that the 500-nm peak assignment to monomer absorption is consistent, we have measured the spectrum of JC1 dye dissolved in methanol where (due to high solubility of the dye) its aggregation is inhibited and only the absorption band of dye monomers can be detected (peak at 517 nm in Figure 4c, isothipendyl dashed line). Taking into account small bathochromic shift caused by solvatochromism , this spectrum confirms the 500-nm band assignment. Figure 4 Absorption spectra of the aqueous solutions. (a) Gold nanostars (black) and their hybrid structures with J-aggregates of JC1 dye without (blue) and with PEI (green); (b) gold nanorods (violet) and their hybrid structure with J-aggregates of JC1 dye (cyan); (c) pristine J-aggregates of JC1 dye (red, solid line) along with the spectra of the solution of JC1 dye in methanol (red, dashed line).