Exciton superradiance in aggregates: The effect of disorder, higher order exciton-phonon coupling and dimensionality

Abstract

In this paper a detailed theoretical analysis is presented of the temperature dependent radiative decay in aggregates of pseudoisocyanine ͑PIC͒. Our approach extends the original linear exciton-phonon coupling model used by Spano, Kuklinsky, and Mukamel ͓Phys. Rev. Lett. 65, 212 ͑1990͔͒ including static disorder and second order exciton-phonon interactions. It is shown that for a one-dimensional exciton model neither of these additional effects alone or in combination with linear electron-phonon coupling can explain the steep rise in radiative lifetime at 40 K observed in the J-aggregate of PIC. However, when the aggregate assembles into a two-dimensional bricklike structure its radiative dynamics can be simulated, with linear exciton-optical phonon coupling as the only source for exciton scattering. Exciton-phonon scattering transfers oscillator strength from the kϭ0 state to other band states and also generates a nonequilibrium population among the exciton states, which persists during the superradiant decay. These effects together explain the marked temperature dependence of the radiative lifetime of the PIC J aggregate. When disorder limits the coherence length at low temperatures to a few molecules, as seems the case in several light harvesting complexes, the exciton population can equilibrate on the time scale of the superradiance. This situation pertains to the strong collision limit of the master equation, where the radiative decay is insensitive to details of the electron-phonon coupling, but only senses change in the thermal population among the exciton states.

Controlled Formation of the Two-Dimensional TTBC J-Aggregates in an Aqueous Solution

“…5,6 Furthermore, their interesting linear and nonlinear optical properties make them promising organic optical materials that could find applications such as ultrasensitive detection of biohazards to superradiance and ultrafast optical switching. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Cyanine dyes can be self-assembled into mesoscopic Jaggregates by short-range noncovalent interactions such as van der Waals interactions, π-π interactions, and hydrogen bonding. Aggregation is a process that is driven mainly by dispersion forces among the nearest neighbor molecules created by the high polarizability of the π-electrons of the polymethine backbone of cyanine.…”

Intraband relaxation and temperature dependence of the fluorescence decay time of one-dimensional Frenkel excitons: The Pauli master equation approach

“…19, unless PIC J-aggregates were assumed to be two-dimensional. 20 The issue of structure and dimensionality of cyanine J-aggregates in solution is a difficult and intriguing one. While usually assumed to be 1D, the nearly linear temperature dependence of the exciton radiative lifetime measured in BIC aggregates has led to the conclusion that these aggregates would be really two-dimensional as well.…”

Low-temperature dynamics of weakly localized Frenkel excitons in disordered linear chains

“…These so-called superradiant states lie near the bottom of the bare exciton band, and, especially at low temperatures, lead to ultrafast spontaneous emission ͑tens to hundreds of picoseconds͒. [5][6][7][8][9][10][11][12][13][14] Upon increasing the temperature, these systems typically exhibit an increase of the fluorescence lifetime, which is a trend that is highly unusual for singlemolecule excitations and is intimately related to the extended nature of the exciton states. This temperature dependence was first observed for the J aggregates of pseudoisocyanine ͑PIC͒, 5,7,8,10 and later confirmed for other types of J aggregates, in particular, 5,5Ј,6,6Ј-tetrachloro-1,1Ј-diethyl-3,3Ј-di ͑4-sulfobutyl͒-benzimidazolocarbocyanine ͑TDBC͒, 11 1,1Ј-diethyl-3,3Ј-bis͑sulfopropyl͒-5,5Ј,6,6Ј-tetrachlorobenzimidacarbocyanine ͑BIC͒, 12 and 3,3Ј-bis͑sulfopropyl͒-5,5Ј-dichloro-9-ethylthiacarbocyanine ͑THIATS͒.…”