Expanded Theory of H- and J-Molecular Aggregates: The Effects of Vibronic Coupling and Intermolecular Charge Transfer

Abstract

The electronic excited states of molecular aggregates and their photophysical signatures have long fascinated spectroscopists and theoreticians alike since the advent of Frenkel exciton theory almost 90 years ago. The influence of molecular packing on basic optical probes like absorption and photoluminescence was originally worked out by Kasha for aggregates dominated by Coulombic intermolecular interactions, eventually leading to the classification of J- and H-aggregates. This review outlines advances made in understanding the relationship between aggregate structure and photophysics when vibronic coupling and intermolecular charge transfer are incorporated. An assortment of packing geometries is considered from the humble molecular dimer to more exotic structures including linear and bent aggregates, two-dimensional herringbone and "HJ" aggregates, and chiral aggregates. The interplay between long-range Coulomb coupling and short-range charge-transfer-mediated coupling strongly depends on the aggregate architecture leading to a wide array of photophysical behaviors.

Understanding the Driving Mechanisms of Enhanced Luminescence Emission of Oligo(styryl)benzenes and Tri(styryl)‐s‐triazine

“…Accordingly, only small spectral shifts (≤0.03 eV) and weak electronic couplings (<71 meV) for both holes ( t h ) and electrons ( t e ) have been computed for the most energetically stable molecular aggregate of 1 in aqueous solution (see Table and Figure S19 in the Supporting Information). Here, it must be remembered that the product, | t h t e |, gives an idea about the short‐range charge‐transfer interactions in the context of the theory reported by Spano and Hestand . The AIEE effect based on the so‐called X aggregates has been reported for different π‐conjugated systems .…”

“…Fortunately, some compounds show enhanced luminescence upon aggregation (aggregation‐induced enhanced emission (AIEE)), which increases their possible applications . Different perspectives are used to explain this phenomenon: from conventional H or J aggregates, originating from Coulombic coupling in the framework of the theory of molecular excitons, to the short‐range excitonic coupling mechanism, due to wavefunction overlap between adjacent molecules . On the other hand, the blocking of nonradiative relaxation by restriction of intramolecular vibrations (RIVs), as well as restricted access to conical intersections (RACIs) between excited and ground states and the blocking of Z / E photoisomerizations are other mechanisms commonly used to interpret AIEE phenomena …”

Dynamically Monitoring Cell Viability in a Dual‐Color Mode: Construction of an Aggregation/Monomer‐Based Probe Capable of Reversible Mitochondria‐Nucleus Migration

“…In this work, we have designed and synthesized af luorescent probe MNQI based on aggregation/monomer mechanism, for the visualization of the two organelles in dual channels,a nd the detection of cell viability.I nS cheme 1, MNQI was constructed with aw eak electronic donor and ac ationic quinolinium group.I tw as ah ydrophobic cation in nature which could be enriched in mitochondria with high negative MMP in healthy cells.Moreover,due to its structural similarity to PIC [24] and high concentration in mitochondria, MNQI forms aggregates with deep-red (DR) emission in healthy cells.…”

Pigmentation of White, Brown, and Green Chicken Eggshells Analyzed by Reflectance, Transmittance, and Fluorescence Spectroscopy

“…The assignment of the Vis‐spectrum uses the fact that dissolved porphyrins tend to aggregate like many other poly‐conjugated molecules by concentration, addition of proteins, adsorption on sol‐gel matrices, and deposition on solid substrates . The weak absorption bands of the monomer broaden and shift by aggregation to the red because the polarizability of the environment becomes higher than the solvent, the strong bands additionally split up into several components.…”