Exciton Dynamics in J- and H-Aggregates of a Tricarbocyanine Near-Infrared Dye

Abstract

Intermolecular interactions in J- and H-aggregates of π-conjugated molecules provide fascinating incentives for excitonic pathways. Investigation regarding exciton dynamics in aggregates of tricarbocyanine near-infrared dyes by transient absorption spectroscopy revealed unusual intermolecular communications not only within different aggregates but also between different aggregates. To this end, aggregation was accompanied by a short-lived excitonic component, that is, on the picosecond time scale, due to additional relaxation channels and a long-lived component, that is, on the nanosecond to microsecond time scales. All of the aforementioned are in sharp contrast to what was found for the monomer. For the monomer, monoexponential exciton dynamics of about 0.5 ns was registered. Overall, the long-lived component in aggregates accounts for 1–5% of all excitons. In J-aggregates, it involves the formation of charge transfer/polaron states. In mixtures of J- and H-aggregates, contributions from the long-lived component further increased. We conclude that interactions between J- and H-aggregates open additional channels for exciton relaxation. One of them is a photoinduced charge transfer from, for example, the bright state in J-aggregates to the dark exciton states in H-aggregates, from where electrons are transferred into the continuum of states.

Structure‐Activity Studies of Nitroreductase‐Responsive Near‐Infrared Heptamethine Cyanine Fluorescent Probes

“…Absorption spectra for probes 5 and 7 (each with a 4’‐ester group and terminal benzoindolinenes) in aqueous buffer solution showed very broad maxima bands indicating the formation of H‐and J‐aggregates (Figure 2). [37] An experiment that injected an aliquot from a concentrated stock solution of probe 5 or 7 (where it is highly aggregated) into a solution of fetal bovine serum immediately produced a spectral profile that indicated extensive probe aggregation but the absorption spectra resolved, over about a 30 minute period, to indicate primarily monomeric probe bound by serum proteins (Figure S6). In the case of probe 9 , the broad absorption profile in aqueous buffer indicated the presence of H‐aggregates (Figure S7a) and there was very weak fluorescence emission.…”

Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems

“…448 The opposite case of energy transfer from the bright level of the J-aggregate to the dark energy level of the H-aggregate was proposed by Dimitriev et al and provides a certain perspective for energy upconversion mediated by a transient absorption of the dark exciton to a higher bright level of the H-aggregate. 449 In a similar way, communication between the polar and the multipolar (quadrupolar, octupolar, etc.) chromophores can occur through the dark states of the latter.…”

“…Kobayashi et al showed that if H-aggregates locate close to J-aggregates with a mutual distance not larger than their physical size and if the density of states of the H-aggregates at the low energy side overlaps with the DOS of the J-aggregates at the high energy side, then the excited H-band can assist J-aggregates to emit fluorescence at the J-band through exciton energy transfer to their optically forbidden high energy state . The opposite case of energy transfer from the bright level of the J-aggregate to the dark energy level of the H-aggregate was proposed by Dimitriev et al and provides a certain perspective for energy upconversion mediated by a transient absorption of the dark exciton to a higher bright level of the H-aggregate …”

Long-Lived Excited State in a Solubilized Graphene Nanoribbon

“…Based on the observed aggregation of nanoribbons in the 2D excitation/emission spectra of Cl-GNR , it is quite likely that the observed transient data contain contributions from both isolated and aggregated ribbons. Since the aggregated ribbons are expected to exhibit short excited-state lifetimes, ,,, the 8.1 ps component is assigned to the excited states of aggregated Cl-GNRs (Figure c). This assignment is consistent with our observations of H-GNR , which exhibits rapid decay on the single to tens of picosecond timescale.…”