Metal–Ligand Complex‐Induced Ultrafast Charge‐Carrier Relaxation and Charge‐Transfer Dynamics in CdX (X=S, Se, Te) Quantum Dots Sensitized with Nitrocatechol

Abstract

The present work describes the effect of interfacial complex formation on charge carrier dynamics in CdX (X=S, Se, Te) quantum dots (QDs) sensitized nitro catechol (NCAT). To compare experiments were also carried out with catechol (CAT) where no such complexation was observed. Time-resolved emission studies suggest faster charge separation in CdS(Se)/NCAT system as compared to CdS(Se)/CAT although change in Gibbs free energy for hole transfer is less in former as compared to later. This suggests that complex formation favours charge separation. Similar studies were also carried out in CdTe/NCAT system where hole transfer process was not viable thermodynamically but due to complex formation charge separation was observed. Femtosecond transient absorption studies have been carried out to monitor charge carrier dynamics in early time scale. Transient studies show faster electron cooling in QDs/NCAT system as compared to pure QDs and has been assigned to the complex formation on QDs surface. Interestingly charge recombination dynamics is much faster in QDs/NCAT system as compared to pure QDs which can be attributed to the stronger coupling between QDs and NCAT. Our results suggest a strong metal-ligand complex formation on QDs surface that controls charge carrier dynamics in QDs/molecular adsorbate system and to the best of our knowledge it has never been reported.

Hot Charge Carriers in Quantum Dots: Generation, Relaxation, Extraction, and Applications

“…In literature a number of studies have been reported on thermal charge carrier extraction from QDs however, hot charge carrier extraction is still not well studied even though the studies on their relaxation dynamics were reported way back in 1990 s . One of the major difficulties with this is the fast charge carrier relaxation time (∼50–250 fs) therefore, to extract hot charge carriers from QDs efficiently, it is important that the extraction time should be less as compared to their relaxation time.…”

“…In literature a number of studies have been reported on thermal charge carrier extraction from QDs [15,16,[19][20][21]74,75] however, Figure 6. Lifetimes of the first excited state of the electron (1P) and hole (2 S 3/2 ) states with excitonic state-to-state selectivity as a function of particle size for hot electron (a), and hot hole (b).…”

“…After generation, they undergo different processes such as recombination, extraction from QDs, trapping etc. depending on the structure of QDs and the surrounding environment . However, the situation becomes interesting and complicated when the QDs are excited by high energy photons (hν‐E g ).…”

“…depending on the structure of QDs and the surrounding environment. [14][15][16][17][18][19][20][21] However, the situation becomes interesting and complicated when the QDs are excited by high energy photons (hν-E g ). In this case the photo-generated charge carriers have excess kinetic energy (hν-E g ) and are excited to higher energy levels of CB and VB respectively ( Figure 1C).…”

Catechol as a Universal Linker for the Synthesis of Hybrid Polyfluorene/Nanoparticle Materials

“…When directly attached to the CPs, which is possible using CTCP in combination with an external catechol-based initiator, the catechol linker retains the conjugation. Small catechol-based molecules and some nonCPs have shown to bind to a variety of commonly used inorganic NPs such as CdS, CdSe, TiO 2 , Fe 3 O 4 , , Au, and ZnO . In addition, we have already prepared a catechol-functionalized poly­(3-alkylthiophene) using a Kumada CTCP (KCTCP) in combination with a catechol external initiator and have proven the formation of a stable coupling to magnetite (Fe 3 O 4 ) NPs .…”