Enhanced Room‐Temperature Photoluminescence Quantum Yield in Morphology Controlled J‐Aggregates

Abstract

Supramolecular assemblies from organic dyes forming J‐aggregates are known to exhibit narrowband photoluminescence with full‐width at half maximum of ≈9 nm (260 cm−1). Applications of these high color purity emitters, however, are hampered by the rather low photoluminescence quantum yields reported for cyanine J‐aggregates, even when formed in solution. Here, it is demonstrated that cyanine J‐aggregates can reach an order of magnitude higher photoluminescence quantum yield (increase from 5% to 60%) in blend solutions of water and alkylamines at room temperature. By means of time‐resolved photoluminescence studies, an increase in the exciton lifetime as a result of the suppression of non‐radiative processes is shown. Small‐angle neutron scattering studies suggest a necessary condition for the formation of such highly emissive J‐aggregates: the presence of a sharp water/amine interface for J‐aggregate assembly and the coexistence of nanoscale‐sized water and amine domains to restrict the J‐aggregate size and solubilize monomers, respectively.

Synthetic Access to Benzimidacarbocyanine Dyes to Tailor Their Aggregation Properties

“…The lower aqueous solubility of the C8S3 compounds warranted the use of the well-established alcoholic method of aggregate preparation, as opposed to their direct dissolution in water (see the Supporting Information for details). We have focused on aqueous systems here to compare with literature studies, but note that blended solutions of water and alkylamines may lead to enhancements in photoluminescence, as reported by Anantharaman and co-workers …”

“…We have focused on aqueous systems here to compare with literature studies, but note that blended solutions of water and alkylamines may lead to enhancements in photoluminescence, as reported by Anantharaman and coworkers. 40 Both of the o-halogenated dyes (C8S3-o-Cl/Br) displayed absorption profiles characteristic of J-aggregate formation following preparation with Milli-Q water, represented in Figure 4a (C8S3-o-Br) and Figures S7 and S8. This selfassembly form is evidenced by the emergence of two sharp absorbance signals at roughly 590 and 600 nm, which have previously been assigned to the J-type aggregates comprising the outer and inner cylinders of the double-walled tubes, respectively.…”

Exciton–Photonics: From Fundamental Science to Applications

“…185,191,192 In this way, monomer molecules which act as exciton trap states can be identified to understand the spatial position of the molecules in large size assemblies using TERS. 193 Further, introducing time-resolved measurements in a near-field technique can be helpful to identify the exciton localization and nonradiative recombination at these exciton traps.…”

“…For instance, using TEPL for nanoimaging and identifying nonradiative spots can also be misinterpreted from photobleaching of organic molecules in ambient conditions. However, the Raman spectrum can show a distinct signature of individual molecules (monomers) and J-aggregates. ,, In this way, monomer molecules which act as exciton trap states can be identified to understand the spatial position of the molecules in large size assemblies using TERS . Further, introducing time-resolved measurements in a near-field technique can be helpful to identify the exciton localization and nonradiative recombination at these exciton traps.…”

“…Additional strategies such as nanopatterning to form resonators are required to enhance coupling of photons with excitons in such self-hybridized systems . Nevertheless, the quantum yield of the J-aggregates requires further enhancement to achieve polariton lasing at room temperature . Finally, understanding of electrical contacts to these materials and developing strategies for stable and reliable contact making will be important moving forward as it will facilitate seamless integration into active devices.…”