Hot‐Hole Extraction from Quantum Dot to Molecular Adsorbate

Abstract

Ultrafast thermalized and hot-hole-transfer processes have been investigated in CdSe quantum dot (QD)/catechol composite systems in which hole transfer from photoexcited QDs to the catechols is thermodynamically favorable. A series of catechol derivatives were selected with different electron-donating and -withdrawing groups, and the effect of these groups on hole transfer and charge recombination (CR) dynamics has been investigated. The hole-transfer time was determined using the fluorescence upconversion technique and found to be 2-10 ps depending on the molecular structure of the catechol derivatives. The hot-hole-transfer process was followed after monitoring 2S luminescence of CdSe QDs. Interestingly, hot-hole extraction was observed only in the CdSe/3-methoxycatechol (3-OCH3) composite system owing to the higher electron-donating property of the 3-methoxy group. To confirm the extraction of the hot hole and to monitor the CR reaction in CdSe QD/catechol composite systems, ultrafast transient absorption studies have been carried out. Ultrafast transient-absorption studies show that the bleach recovery kinetics of CdSe QD at the 2S excitonic position is much faster in the presence of 3-OCH3. This faster bleach recovery at the 2S position in CdSe/3-OCH3 suggests hot-hole transfer from CdSe QD to 3-OCH3. CR dynamics in CdSe QD/catechol composite systems was followed by monitoring the excitonic bleach at the 1S position and was found to decrease with free energy of the CR reaction.

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

“…It is clear from Figure A, B that the luminescence decay traces of CdS and CdSe QDs are much faster with CAT and NCAT as compared to pure QDs decay. This faster luminescence decay in the presence of CAT and NCAT can be attributed to the hole‐transfer process from QDs to CAT and NCAT as mentioned above and also described earlier . It is interesting to see from Figure A, B that the emission kinetics decay trace is much faster in QDs/NCAT composite system as compared to QDs/CAT composite although −Δ G HT ° value for hole–transfer reaction is less in the former as compared to the latter.…”

“…have studied the charge separation in zinc porphyrin–QD complexes where they have shown electron transfer from zinc porphyrins to QDs. In our earlier investigations we also demonstrated ultrafast charge separation in binary systems of CdSe and CdS QDs with different molecular adsorbates . In all the above stated reports different molecules were chosen that acts as either hole‐ or electron‐transporting molecules for QDs with an aim to get better charge separation.…”

Tuning Hole and Electron Transfer from Photoexcited CdSe Quantum Dots to Phenol Derivatives: Effect of Electron‐Donating and ‐Withdrawing Moieties

“…The bleaching recovery kinetics in femtosecond TA for the CdSe/4NP composite becomes much faster than that of CdSe QDs (at the same time, the bleaching intensity decreases drastically), whereas for CdSe/4MP the bleaching recovery kinetics becomes slower. [23,[63][64][65] In addition, in our earlier investigation, [52] we observed in CdSe/p-methoxycatecholt hat the paramethoxy moiety introduces as trong electron-donating ability, which makes the molecule easy to oxidize, and thus, it acts as as trong hole-accepting molecule. [67] They observedt hat BQ rapidly quenched electrons from the CB of CdSe QDs with the formation of as hortlived CT state, with al ifetime of 2.7 ps, which resulted in faster bleaching recovery kinetics.…”

“…[52] Recently,A livisatos et al reported that, upon changing the substituent from electron donating to withdrawing, the rate of hole transfer could be tuned from CdSe/CdS to different ferrocened erivatives. [52] Recently,A livisatos et al reported that, upon changing the substituent from electron donating to withdrawing, the rate of hole transfer could be tuned from CdSe/CdS to different ferrocened erivatives.…”

“…[53] The tunability of the rate of hole transfer can be achieved through only the substituent. [48,[52][53][54] It will be interesting to study the PL and lifetimeq uenching of QDs with organic molecules containing electron-withdrawing and -donating moieties and understanding the effect on ultrafast CT dynamics. [48] Their analysis suggested that strongly electron-donating para-substituted anilines quenched the QD emission through photoinduced hole transfer;h owever,t he predominant interaction fors trongly electron-withdrawing para-substituted anilines was passivation of Cd 2 + sites through s donation.…”