High-Stability, High-Efficiency Organic Monoliths Made of Oligomer Nanoparticles Wrapped in Organic Matrix

Abstract

Oligomer nanoparticles (OL NPs) have been considered unsuitable for solid-state lighting due to their low quantum yields and low temperature stability of their emission. Here, we address these problems by forming highly emissive and stable OL NPs solids to make them applicable in lighting. For this purpose, we incorporated OL NPs into sucrose matrix and then prepared their all-organic monoliths. We show that wrapping the OL NPs in sucrose significantly increases their quantum yield up to 44%, while the efficiency of their dispersion and direct solid-film remain only at ∼6%. We further showed ∼3-fold improved temperature stability of OL NP emission within these monoliths. Our experiments revealed that a physical passivation mechanism is responsible from these improvements. As a proof-of-concept demonstration, we successfully employed these high-stability, high-efficiency monoliths as color converters on a blue LED chip. Considering the improved optical features, low cost, and simplicity of the presented methodology, we believe that this study holds great promise for a ubiquitous use of organic OL NPs in lighting and possibly in other photonic applications.

Highly Luminescent CB[7]‐Based Conjugated Polyrotaxanes Embedded into Crystalline Matrices

“…We attribute the enhancement in the QY mainly due to the presence of CB7s which decreases the chain–chain interactions by isolating the chains. Interestingly, we did not observe any profound change in the fluorescence spectra of polymer and polyrotaxane solutions ( Figure ), which is not in alignment with our previous findings . We believe that the high concentrations of polymers and polyrotaxanes used in this work may have caused this variation.…”

“…Even though polymers in sucrose perform slightly better than other hosts that were tested here, their QY remained to be low as around 10%. This is in contrast with the nanoparticles of conjugated oligomers, which had shown strong improvement in QY when embedded into sucrose host . Different than the conjugated oligomer nanoparticles, the polymers in the absence of CB7 encapsulation exhibited a strong red‐shift in their fluorescence spectra compared to their solution (Figure ; Figure S2, Supporting Information) especially at high amounts of loading into the host matrix.…”

“…In line with these trends, we measured longer fluorescence lifetimes of the polymers in all the hosts compared to the polymer solid film while they remained shorter in comparison with the fluorescence lifetime of the polymer solution (Figure ; Figure S3, Supporting Information). All these observations bring us to the conclusion that the molecules of the host medium cannot efficiently passivate the nonradiative transitions of the open polymer chains without CB7‐threading as opposed to the case of conjugated oligomer nanoparticles …”

“…These mixtures were left to crystallize under ambient temperature and pressure on a vibration absorbing pad. The incorporation levels of the added molecules were tested by redissolving the powders in water, measuring the absorbance levels, and comparing with the polyrotaxane solution indicated almost complete incorporation, which has been the case for our previous works as well . Obtained crystals were then powdered using a mortar.…”

“…Moreover, this method was also extended to nonionic crystals including sucrose and anthracene and to quantum dots in nonpolar solvents and applied in light‐emitting diodes (LEDs) and sensors . Recently, our group has evaluated the potential of this technique by incorporating the conjugated oligomer nanoparticles, which are essentially wrapped in the form of nanoscale balls of oligomers in sucrose crystals . The QY of the nanoparticles in sucrose powders significantly increased even compared to the nanoparticle solution while the emission stability at elevated temperatures was substantially improved.…”