Mixed Organic Ligand Shells: Controlling the Nanoparticle Surface Morphology toward Tuning the Optoelectronic Properties

Abstract

synthetic fibers and resins, [4] imaging dyes in bioanalysis, [5] light harvesting applications, [2,6,7] electron transport materials in thin films, [8,9] to monolayer field effect transistors. [9][10][11][12] The nature of PBIs, that is, their extended π-systems, is the inception to strong hydrophobic π-stacking interactions, which ultimately influences the optical properties. [1,2,13] Controlling the PBI aggregation is, however, crucial in the context of applications. For example, the size and morphology of pigments are critical tools to govern the resulting color brilliance. Consequently, suitable and easy applicable methods for fine-tuning the optical properties are at great demand. Depending on the type of aggregates, the fluorescence properties differ, too. Coulombic coupling between, for example, individual PBIs is mainly responsible for the underlying trend. [14] To this end, the alignment of their transition dipoles is crucial as it goes hand-in-hand with changes in the radiative decay rate and shifts in the absorptions. On one hand, H-aggregates feature "side-by-side" aligned transition dipole moments, from which blueshifted absorptions and a suppressed radiative decay compared to monomeric PBIs originate. On the other hand, Precise control over the ratio of perylene bisimide (PBI) monomers and aggregates, immobilized on alumina nanoparticle (NP) surfaces, is demonstrated.Towards this goal, phosphonic acid functionalized PBI derivatives (PA-PBI) are shown to self-assemble into stoichiometrically mixed monolayers featuring aliphatic, glycolic, or fluorinated phosphonic acid ligands, serving as imbedding matrix (PA-M) to afford core-shell NPs. Different but, nevertheless, defined PBI monomer/aggregate composition is achieved by either the variation in the PA-PBI to PA-M ratios, or the utilization of different PA-Ms. Various steady-state as well as time-resolved spectroscopy techniques are applied to probe the coreshell NPs with respect to changes in their optical properties upon variations in the shell composition. To this end, the ratio between monomer and excimerlike emission assists in deriving information on the self-assembled monolayer composition, local ordering, and corresponding aggregate content. With the help of X-ray reflectivity measurements, accompanied by molecular dynamics simulations, the built-up of the particle shells, in general, and the PBI aggregation behavior, in particular, are explored in depth.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Smart Shell‐by‐Shell Nanoparticles with Tunable Perylene Fluorescence in the Organic Interlayer

“…With the results of TGA measurements, grafting densities of 4.29 nm −2 for the Al 2 O 3 ‐(PAR 1 10 % PAR 2 90 % ) hybrids and 3.02 nm −2 for the Al 2 O 3 ‐(PAR 1 10 % PAR 2 90 % ) hybrids were obtained (see Figure S3). The fact, that phosphonic acid mixtures can be stoichiometrically displayed onto metal oxide surfaces, was already corroborated in recent studies [4b, 5, 8, 9, 15, 16] . TGA measurements of Al 2 O 3 NPs functionalized with different ratios of PAR 1 and PAR 2 /PAR 3 were shown in the supporting information (Figure S3) and displayed the differences in the grafting densities as well as in the DTG curves.…”

“…Fluorocarbon moieties are more rigid than hydrocarbons [18] and are thus more suitable for separating the perylene cores onto the NP surface and prevent excimer formation, resulting in more structured fluorescence signals of the Al 2 O 3 ‐(PAR 1 10 % PAR 3 90 % ) NPs. This has already been seen for pyrene and perylene bisimide functionalized Al 2 O 3 NPs by using either hydrocarbon or fluorocarbon spacing phosphonic acids [5, 8] …”

“…Responsible for the quenching is a photo‐induced electron‐transfer (PET) from the LUMO of the PAHs excited state towards the LUMO of the positively charged nitrogen atom of the pyridinium unit, that has a lower energy level [7] . Recently, we demonstrated that the type and nature of spacing phosphonic acids influences the aggregation of perylene bisimides (PBIs) onto Al 2 O 3 NP surfaces and thus the optical properties of the PBIs [8] . Whereas the rigid fluorocarbon phosphonic acids separate the PBI units very effectively, interactions of PBIs with hydrocarbon phosphonic acids are less hindered.…”

Wafer‐Scale Organic Complementary Inverters Fabricated with Self‐Assembled Monolayer Field‐Effect Transistors

“…As p-type semiconductors, benzothieno [3,2-b][1]benzothiophenes (BTBTs) were used as unsymmetrically alkyl-substituted derivatives either with phosphonic acid anchor group for self-assembly or without that for being evaporated. [20][21][22] The same concept was adopted to n-type molecules based on 3,4,9,10-perylene tetracarboxylic diimides (PTCDIs), [23,24] so that finally two SAM molecules (pand n-type) and two corresponding small molecules for evaporation (n-and p-type) build the basis for our systematic study.…”

Proximity Effects of Methyl Group on Ligand Steric Interactions and Colloidal Stability of Palladium Nanoparticles

“…Nanoparticles serve as a bridge between atoms and bulk materials, exhibiting a variety of unique chemical, physical, and electronic characteristics (Lohse and Murphy, 2012 ; Heiligtag and Niederberger, 2013 ; Henkel et al, 2020 ). However, the high surface area of small nanoparticles usually decreases the colloidal stability of nanoparticles and causes uncontrolled agglomeration producing thermodynamically favorable large or bulk materials (Ingham et al, 2011 ; King et al, 2018 ).…”