Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with J-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π–π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.

EDGE ARTICLEAndrew J. deMello, Joshua B. Edel et al. Rapid cell extraction in aqueous twophase microdroplet systems PERSPECTIVE Barry M. Trost et al. Catalytic asymmetric allylic alkylation employing heteroatom nucleophiles: a powerful method for C-X bond formation

Colloidal metal‐halide perovskite nanocrystals (MHP NCs) are gaining significant attention for a wide range of optoelectronics applications owing to their exciting properties, such as defect tolerance, near‐unity photoluminescence quantum yield, and tunable emission across the entire visible wavelength range. Although the optical properties of MHP NCs are easily tunable through their halide composition, they suffer from light‐induced halide phase segregation that limits their use in devices. However, MHPs can be synthesized in the form of colloidal nanoplatelets (NPls) with monolayer (ML)‐level thickness control, exhibiting strong quantum confinement effects, and thus enabling tunable emission across the entire visible wavelength range by controlling the thickness of bromide or iodide‐based lead‐halide perovskite NPls. In addition, the NPls exhibit narrow emission peaks, have high exciton binding energies, and a higher fraction of radiative recombination compared to their bulk counterparts, making them ideal candidates for applications in light‐emitting diodes (LEDs). This review discusses the state‐of‐the‐art in colloidal MHP NPls: synthetic routes, thickness‐controlled synthesis of both organic–inorganic hybrid and all‐inorganic MHP NPls, their linear and nonlinear optical properties (including charge‐carrier dynamics), and their performance in LEDs. Furthermore, the challenges associated with their thickness‐controlled synthesis, environmental and thermal stability, and their application in making efficient LEDs are discussed.

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.