Mapping Forbidden Emission to Structure in Self-Assembled Organic Nanoparticles

Abstract

The interplay between micromorphology and electronic properties is an important theme in organic electronic materials. Here, we show that a spirofluorenefunctionalized boron-dipyrromethene (BODIPY) with an alkyl norbornyl tail self-assembles into nanoparticles with qualitatively different properties as compared to the polymerized species. Further, the nanoparticles exhibit a host of unique emissive properties, including photobrightening, a blue satellite peak, and spectral diffusion. Extensive photophysical characterization, including single-particle imaging and spectroscopy, and time-resolved fluorescence, coupled with electronic structure calculations based on an experimentally determined crystal structure, allow a mechanism to be developed. Specifically, BODIPY chromophores are observed to form quasi-two-dimensional layers, where stacking of unit cells adds either J-aggregate character or H-aggregate character depending on the direction of the stacking. Particularly strongly H-coupled domains show the rare process of emission from an upper exciton state, in violation of Kasha's rule, and result in the blue satellite peak. The spatial heterogeneity of structure thus maps onto a gradient of photophysical behavior as seen in single-particle imaging, and the temporal evolution of structure maps onto fluctuating emissive behavior, as seen in single-particle spectroscopy. Taken together, this system provides a striking example of how physical structure and electronic properties are intertwined, and a rare opportunity to use one to chart the other.

Self-Assembly of Porphyrin Dipeptide Conjugates toward Hydrogen Production

“…Among small peptides, diphenylalanine (Phe-Phe, FF) is the most extensively studied dipeptide for its self-assembling properties. , Numerous chromophores such as BODIPYs, porphyrins, , corroles, POMs, and ferrocene have been coupled through covalent bonds to Phe-Phe, and the resulting conjugates retained the characteristic of forming self-assembling nanostructures. The self-assembled chromophores demonstrated distinct and improved properties compared to their initial monomers and found application in photothermal therapy and other light-harvesting applications. − …”

From absorption spectra to charge transfer in PEDOT nanoaggregates with machine learning

“…The electronic properties of organic materials are highly sensitive to the packing of composing molecules hence dependent on the processing conditions. 18 Fast optical probing of local electronic couplings can benefit both applied and fundamental research. On one hand, such a method brings the possibility to combine continuous testing of devices with roll-to-roll device manufacturing technology.…”

Photocatalytic hydrogen production of porphyrin nanostructures: spheres vs. fibrils, a case study

“…14 The self-assembled chromophores have illustrated distinct properties compared to their initial monomer derivatives in many different scientific fields. [15][16][17][18][19] There has been a prevalent interest in the preparation of self-assembled porphyrin nanostructures, aiming to imitate natural light harvesting processes in order to develop new nanostructured materials for photocatalytic processes. More specifically, self-assembled nanostructures have been used in photothermal therapy, 16 in light harvesting applications 17 and also as fluorescent probes and in data storage devices.…”