Photodynamics at the CdSe Quantum Dot–Perylene Diimide Interface: Unraveling the Excitation Energy and Electron Transfer Pathways

Abstract

Excitation energy and charge transfer processes in perylene diimide dye−CdSe quantum dot complexes have been studied by femtosecond transient absorption spectroscopy. After excitation of the quantum dots high above the band edge, the electronically excited perylene diimide forms on a timescale similar to the ultrafast quantum dot intraband relaxation. An extraordinarily fast energy transfer time of <300 fs is determined, indicating that the transfer from the hot excitonic state competes with quantum dot intraband relaxation. A much slower kinetic component is attributed to the energy transfer from the quantum dot's lowest excitonic state to perylene diimide. At high dye−quantum dot ratios, the electronically excited dye generated in the energy transfer reaction is reduced by an electron transfer from the quantum dot ground state. This study demonstrates the potential of the investigated organic−inorganic hybrid for the design of tailor-made energy transfer systems, which can be applied in the emerging field of hot exciton utilization.

Ultrafast spectroscopy studies of carrier dynamics in semiconductor nanocrystals

“…While charge transfer to/from adsorbed ligands on nanocrystal surfaces are not the focus of this review article, it must be acknowledged that charge transfer is a process that competes with surface trapping and plays a pivotal role in the fate of the excited state when adsorbed to the nanocrystal ( Dworak et al., 2021 ; Logunov et al., 1998 ; Zhu et al., 2012 ). Early work found that electron transfer from the nanocrystal to an electron acceptor such as methyl viologen occurs in 200–300 fs and therefore competes with surface trapping and electron-hole recombination processes, quenching both band gap and deep trap emission and creating a long-lived charge-separated state ( Logunov et al., 1998 ).…”

Ultrafast separation of multiexcitons within core/shell quantum dot hybrid systems

“…Consequently, it is assumed that on average 2.1-2.4 MB molecules are electrostatically bound to one QD. It is known that electron and energy transfer times are accelerated with increasing acceptor concentration 29,[32][33][34] but due to the similarity of these ratios, we assume that the small concentration differences only play a minor role for the modulation of the electron transfer rates.…”

Spektroskopische Charakterisierung von Halbleiter-Quantenpunkten und deren Hybridsystemen

“…[98] Die Exzitonen üben einen Stark-Effekt auf die Zustände aus und bedingen so eine Veränderung der Größe der Bandlücke. [98,99] Um das Signal-zu-Rausch-Verhältnis zu verbessern, werden mehrere Scans pro Probe und Anregungspuls aufgenommen. Ein Scan beinhaltet eine vollständige Messung der transienten Absorption für die eingestellte Verzögerungszeit von Anreg-zu Abtastpuls.…”

“…Die Ergebnisse dieser Studie konnten 2021 veröffentlicht werden. [99] 7 ten Pikosekunde aufgrund von Intraband Relaxation zerfällt. [29,35,98,99] Neben den TA Daten der puren CdSe Quantenpunkte sind auch die Spektren exemplarisch ausgewählter Hybridsysteme gezeigt.…”

“…[99] 7 ten Pikosekunde aufgrund von Intraband Relaxation zerfällt. [29,35,98,99] Neben den TA Daten der puren CdSe Quantenpunkte sind auch die Spektren exemplarisch ausgewählter Hybridsysteme gezeigt. Betrachtet man die Spektren der Hybridsysteme so können die Signaländerungen bei kurzen Verzögerungszeiten der Quantenpunktkomponente zugeordnet werden.…”