Non-Kasha Behavior in Quadrupolar Dye Aggregates: The Red-Shifted H-Aggregate

Abstract

Aggregates of quadrupolar DAD-type chromophores are investigated theoretically using the essential states model (ESM) enhanced to include vibronic coupling. On the basis of vibronic signatures in the absorption and photoluminescence spectra, important connections are made to the Frenkel exciton model, which is the basis for defining conventional H-and J-aggregates. In contrast to the exciton theory, the ESM allows for an unusual type of the red-shif ted Haggregate, driven by the large quadrupole−quadrupole interaction. Except for the red shift of the main absorption peak, such aggregates display all of the characteristics of conventional Haggregates, including suppressed radiative decay rates and all of the vibronic signatures in the absorption and photoluminescence spectra consistent with Frenkel exciton models. Red-shifted Hdimers occur for a range of slip angles, which separate conventional H-and J-aggregate behavior, with the slip range diminishing with increasing intermolecular separation. Davydov splitting and vibronic signatures for dimers with nonparallel transition dipole moments are also investigated. The theoretical insight provided herein may be exploited for optimizing optoelectronic device applications for growing families of quadrupolar molecules.

Polymorphic chiral squaraine crystallites in textured thin films

“…From this, we can find a structural model for the molecular alignment based on simple exciton theory …”

“…Here, the x‐component resembles the LDC or J‐like component with red‐shifted transition energy. Likewise, the y ‐component gives the UDC or H‐like component with blue‐shifted transition energy . For graphical vector addition of the projected TDM as sketched in Figure A, the x ‐component is along the long brick axis and the y ‐axis is along the short brick axis.…”

Controlling the structure and photophysics of fluorophore dimers using multiple cucurbit[8]uril clampings

“…Moreover, such a modular molecular design towards quadrupolar uorescent molecules may provide a feasible toolbox in pursuit of distinct features such as large two-photon cross-sections 66,67 and non-Kasha behavior. 68 On the practical side, CB[7]-and CB[8]mediated uorescent complexes developed here are promising candidates for various (biological) imaging applications on account of their emergent photophysical properties such as long lifetimes, high emission brightness, and red-shied excitation bands.…”

Exciton Interactions, Excimer Formation, and [2π+2π] Photodimerization in Nonconjugated Curcuminoid‐BF2 Dimers

“…Mixing between Frenkel and charge‐transfer excitations is important in determining the optical properties of tightly packed solid‐state assemblies . Moreover, aggregation of quadrupolar dyes has been observed to induce large redshifts of the absorption, leading to redshifted H‐aggregates as a result of a non‐Kasha behavior . We are currently investigating these directions with the design of nonconjugated dimers in which the interaction between dye subunits is modulated by linkers with tailored folding behavior.…”

“…However, because of their quadrupolar electronic structure, D‐π‐A‐π‐D dyes exhibit intriguing properties in the solid state emerging from the quadrupole–quadrupole interactions. The latter was shown to provide a route to nonconventional H‐aggregates with a redshifted absorption as a result of a non‐Kasha behavior …”