By employing a colloid chemical reaction method we demonstrate the preparation of organic nanoparticles composed of perylene molecules (PeNPs) based on the reduction of perylene perchlorate by Br- anions in the presence of cetyl trimethyl ammonium bromide (CTA+Br-) in acetonitrile. A discrete nucleation event, followed by a slower controlled growth on the existing particles, is identified during formation of PeNPs. By changing the growth parameters, such as the monomer concentration and the method of injection, quasi-spherical PeNPs with controllable sizes from 25 to 90 nm could be obtained. The homogeneous solution phase of this method makes it capable of large-scale synthesis of PeNPs with a size distribution (<10%) that is improved by formation of a protective layer of CTA+ around the PeNPs. The three-dimensional, hierarchical self-organization of 25-nm PeNPs building blocks is observed to form nanobelts and square nanorods, possibly templated by the CTA+ lamellar micelle structures in acetonitrile. Spectroscopic results reveal two kinds of trends in the development of the optical properties of perylene as they evolve from the molecular to the bulk phase in the nanometer range. The so-called size dependence is evidenced by a switch from Y-type to E-type excimers as the size of the PeNPs increased from 25 to 90 nm. As the 25-nm PeNPs organize into nanobelts or square nanorods the oscillator strength of the Y-type excimers is relatively enhanced. That is, collective phenomena develop as the proximal particles interact in the glassy solids. Our very recent results indicate that this colloid chemical reaction method can also be applied to other organic compounds.

Colloid chemical reaction route to the preparation of nearly monodispersed perylene nanoparticles: size-tunable synthesis and three-dimensional self-organization.

Two-dimensional single-crystalline nanostructures of perylene with uniform square and rhombus shapes have been prepared successfully via a simple reprecipitation method with the assistance of surfactant CTAB templates. The X-ray diffraction (XRD) measurements reveal that the square and rhombus nanosheets can be indexed to α- and β-phase perylene crystals, respectively. On the basis of the analysis of time-dependent growth processes, we found that selective adhesion of CTAB molecules on the crystal (001) plane facilitates to the formation of sheetlike structures, whereas polymorph transition from α- to β-phase achieved by altering the surfactant CTAB concentration results in the evolution of the nanosheet from square to rhombus morphologies. Single-nanoparticle spectrscopy depicts that square and rhombus nanosheets show distinct shape-dependent optical properties that are directly related to their crystal structures. Furthermore, the optical waveguiding behaviors have been revealed through the scanning nea...

Phase- and Shape-Controlled Synthesis of Single Crystalline Perylene Nanosheets and Its Optical Properties

The spectroscopic and photophysical properties of organic materials in the solid-state are widely accepted as a result of their molecular packing structure and intermolecular interactions, such as J- and H-aggregation, charge-transfer (CT), excimer and exciplex. However, in this work, we show that Spe-F4DIB cocrystals (SFCs) surprisingly retain the energy levels of photoluminescence (PL) states of Spe crystals, despite a significantly altered molecular packing structure after cocrystallization. In comparison, Npe-F4DIB cocrystals (NFCs) with new spectroscopic states display different spectra and photophysical behaviors as compared with those of individual component crystals. These may be related to the molecular configuration in crystals, and we propose Spe as an “intramolecular emissive” material, thus providing a new viewpoint on light-emitting species of organic chromophores. Moreover, the nonlinear optical (NLO) properties of Npe and Spe are firstly demonstrated and modulated by cocrystallization. The established “molecule-packing-property” relationship helps to rationally control the optical properties of organic materials through cocrystallization.

Uncovering the Intramolecular Emission and Tuning the Nonlinear Optical Properties of Organic Materials by Cocrystallization

Steady-state and picosecond time-resolved fluorescence spectra of perylene have been measured in order to examine the dimer formation and the excitation relaxation in restricted geometries of Langmuir−Blodgett (LB) films. In LB films, perylene forms two types of dimers, D1 and D2, which are assigned to the dimers where two chromophores are partially and fully overlapped, respectively. At the concentration of 0.05 mol %, only the monomer fluorescence is observed. As the concentration is increased to 1 mol %, the excimer 1 fluorescence (from D1 site) can be seen in the time region after 40 ns. At a concentration higher than 10 mol %, all three components including the excimer 2 fluorescence (D2) are observed from the early stage of time. Their contributions to the steady-state and the time-resolved fluorescence spectra are dependent upon the concentration. The excitation transfer from M (monomer) and D1 sites to the D2 site occurs with a time constant of ∼50 ps at a concentration of 10 mol %, whereas it is ...

Dimer Formation and Excitation Relaxation of Perylene in Langmuir−Blodgett Films

This paper describes a combined experimental and theoretical simulation investigation on the photophysical properties, thermolysis, and orientation of 3,4,9,10-perylene tetracarboxylate (PTCB) intercalated Mg-Al-layered double hydroxide (PTCB/Mg-Al-LDH). UV-vis absorption and fluorescence spectroscopy show the existence of PTCB aggregates within the gallery of LDH, indicative of H-type (blue-shifted absorption band) and J-type dimers (red-shifted absorption band). In situ high-temperature X-ray diffraction (HT-XRD), thermogravimetry and differential thermal analysis (TG-DTA) and elemental analysis were used to study the thermal decomposition properties of PTCB/Mg-Al-LDH, and it was found that the decomposition temperature of the intercalated PTCB is lower than its pristine form (460 vs 565 degrees C), indicating that the strong pi-pi interaction among PTCB was weakened by the positively charged LDH host layers. Molecular dynamics (MD) calculations were employed to simulate the molecular arrangement and aggregation behavior of intercalated PTCB in the gallery of Mg-Al-LDH. The simulation results show that the intercalated PTCB anions exhibit a tendency from tilted to vertical orientation with respect to the layers as the interlayer water content increases, furthermore, the H and J-type dimer species are most likely populated under low and high hydration conditions, respectively. Moreover, the distribution of interlayer water molecules are also discussed.

A combined study based on experiment and molecular dynamics: perylene tetracarboxylate intercalated in a layered double hydroxide matrix

In this paper, E-excimer and Y-type luminescence of perylene dimers in a Langmuir-Blodgett film appear to represent excimer formation in sandwich dimers in the absence of crystalline order. Y-emission has a very weak temperature dependence. E-emission can be generated through the partially forbidden transition to the lowest excited dimer state. 24 refs., 6 figs.

E-excimer and Y-type luminescence of perylene dimers in a Langmuir-Blodgett film at 1.5 K

Fluorescence spectra of anthracene moieties with fatty acid tails attached at the 2-position are reported for Langmuir-Blodgett(LB)-type multilayer configurations obtained as single crystals in the gas phase. These systems are considered the best ordered experimental model systems for chromophores with fatty acid tails arranged in the LB multilayer configuration. Closest agreement of the fluorescence spectrum with that of the unsubstituted anthracene crystal is found for the 4-(2-anthryl)-1-butanoic acid (2A4) crystal. Packing of the anthracene moieties is very similar in both crystals. Low-temperature spectra (10 K) reveal strong broadening of the peaks due to spatial disorder in the 2A4 crystal. 7-(2-Anthryl)-1-heptanoic acid (2A7) crystals and even more so actual 2A7 LB multilayers have less structured fluorescence spectra that extend further to lower energies. Picosecond time resolved fluorescence decay curves show exciton transport and trapping in low energy traps. Compressed ground state pairs with excimer-type spatial configurations are excited directly in the red (476 nm) to emit structureless excimer-type fluorescence.

Fluorescence as probe for transport and lateral order in vapor grown Langmuir-Blodgett(LB) multilayer-type single crystals of anthracene chromophores with fatty acid tails

W. Storck

Papers

E-excimer and Y-type luminescence of perylene dimers in a Langmuir-Blodgett film at 1.5 K

Fluorescence as probe for transport and lateral order in vapor grown Langmuir-Blodgett(LB) multilayer-type single crystals of anthracene chromophores with fatty acid tails