Excimer-Mediated Intermolecular Charge Transfer in Self-Assembled Donor–Acceptor Dyes on Metal Oxides

Abstract

When conjugate molecules are self-assembled on the surface of semiconductors, emergent properties resulting from the electronic coupling between the conjugate moieties are of importance in the interfacial electron-transfer dynamics for photoelectrochemical and optoelectronics devices. In this work, we investigate the self-assembly of triphenylamine–oligothiophene–perylenemonoimide (PMI) molecules, denoted as BH4, on metal oxide surfaces via UV–vis absorption, photoluminescence, and transient near-infrared absorption spectroscopies and molecular dynamics simulations, and we report the excimer formation due to the π–π interaction of the PMI units between the neighboring dye molecules. To our best knowledge, this is the first experimental observation of intermolecular excimer formation when conjugate donor–acceptor molecules form a self-assembled monolayer. In addition, a long-lived (4.3 μs) intermolecular charge separation is observed, and a new excimer-mediated intermolecular charger-transfer mechanism is proposed. This work demonstrates that, through the design of dye molecules, the excited complexes or aggregates can provide a pathway to slow down the recombination rate in photoelectrodes that utilize donor–acceptor dyad molecules.

Ultrafast Dynamics and Photoresponse of a Fungi‐Derived Pigment Xylindein from Solution to Thin Films

“…In particular, the ESA intensity from 710–740 nm shows a gradual increase with increasing concentrations, albeit a sharp decrease is apparent for the highest concentration (Figure 2 c) and thin films (Figure 2 d), primarily due to ground‐state bleaching (GSB) of the aggregated species. Most strikingly, we observed a sign reversal of the xylindein TA signal from about 850–900 nm: the negative SE band in solution (Figure 2 a–c) is replaced by a positive ESA band in thin films (Figure 2 d), generally attributable to an excimer→charge‐transfer band transition (see below) [9, 13] …”

“…Most strikingly,w eo bserved as ign reversal of the xylindein TA signalf rom about 850-900 nm:t he negative SE band in solution ( Figure 2a-c) is replacedb yapositive ESA band in thin films (Figure 2d), generally attributable to an excimer!charge-transfer band transition (see below). [9,13] Global analysiso ft he fs-TAs pectra retrieves intrinsic timescales of the underlying excited-state processes. [11a, 14] In xylindein solution,t he spectra can be fit with ao ne-component model with an approximately 30 ps lifetime for three low concentrations( Figure S7), substantiated by the probe-dependent least-squares exponentialf its ( Figure S8).…”

Bacterial Cellulose Composite Solid Polymer Electrolyte With High Tensile Strength and Lithium Dendrite Inhibition for Long Life Battery

“…Although the energy gap between HOMO and LUMO of PEO/BC composite is smaller than that of PEO (6.45 eV vs 7.27 eV), their spatial separation requires an unfavorable intermolecular charge transfer besides intramolecular charge transfer during redox reactions. [ 31–33 ] Thus, the higher potentials could be withstood.…”

Elucidating Inner Workings of Naturally Sourced Organic Optoelectronic Materials with Ultrafast Spectroscopy

“…Interestingly, a distinctive sign reversal of TA signal was observed from the negative SE arising from ESIPT in solution to a positive ESA in thin films (Figure 3b, ∼850–900 nm). The ESA feature likely originates from an excimer state, which accesses a higher‐lying CT state upon intermolecular electron transfer within the excimer [15b,57] . Global analysis of the thin‐film TA spectra retrieves three time constants of ∼620 fs, 6.8 ps, and 635 ps representing the exciton self‐trapping, structural optimization, and return to S 0 (see Figures 3d and g).…”