Hot Electron Transfer from CdTe Quantum Dot (QD) to Porphyrin and Ultrafast Electron Transfer from Porphyrin to CdTe QD in CdTe QD–Tetrakis(4-carboxyphenyl)porphyrin Nanocomposites

Abstract

Understanding of exciton dynamics in semiconductor quantum dots (QDs) is of great importance due to their immense application potential on various photonic devices. In this work, we demonstrate hot electron transfer (HET) from higher excited states of cadmium telluride quantum dots (CdTe QDs) to tetrakis(4-carboxyphenyl)porphyrin (TCPP) and ultrafast electron transfer from photoexcited TCPP to CdTe QDs in newly prepared CdTe QD−tetrakis(4-carboxyphenyl)porphyrin nanocomposites (CdTe QD−TCPP NCs), where TCPP is noncovalently attached to CdTe QDs, by employing steady state, time-resolved emission, and femtosecond transient absorption spectroscopic techniques. The observation of efficient quenching of the photoluminescence (PL) of CdTe QDs with little/negligible change in photoluminescence (PL) decay profiles in nanosecond time regime (TCSPC method) of CdTe QD−TCPP NCs predominantly indicates static interaction between these two interacting species, CdTe QD and TCPP. Excitation wavelength and excitation intensity dependent femtosecond transient absorption studies of CdTe QDs and CdTe QD−TCPP NCs confirm the hot electron transfer (HET) from higher excited states (Σ − /1P(e)) to TCPP. Analysis of growth kinetics of band-edge or 1S bleach amplitude of band-edge bleach signal strength at the initial stage after excitation allows us to estimate 30−40% quantum efficiency (Φ HET ) of HET when CdTe QD−TCPP NCs are excited at higher excited state (∼390 nm). In contrast, no electron transfer was observed when CdTe QD−TCPP NCs are excited in the vicinity of the band-edge (1S) exciton. In another instance, femtosecond transient absorption studies upon 630 nm excitation at the Q-band of TCPP in CdTe QD−TCPP NCs suggest the occurrence of ultrafast electron transfer (<250 fs) from photoexcited TCPP to CdTe QDs in CdTe QD−TCPP NCs. The charge separation and charge recombination dynamics in CdTe QD−TCPP NCs are explored in detail. The fundamental understanding of this "to and fro" photoinduced electron transfer dynamics in CdTe QD−TCPP NCs opens up new possibilities to design an efficient light-harvesting system based on inorganic−organic hybrid systems.

Triplet generation at the CdTe quantum dot/anthracene interface mediated by hot and thermalized electron exchange for enhanced production of singlet oxygen

“…21 The hot electron relaxation time ( τ HERT ) of the CdTe QDs decreases from 159 ± 12 fs to 115 ± 13 fs in the presence of ACA, as extracted by exponential fitting from Fig. 3(f), and then the efficiency of hot electron exchange mediated TET ( φ TET ) can be determined to be ∼27% with 530 nm excitation using the following equation, 34,41 …”

Mechanistic Insights into Selective Sensing of Pb2+ in Water by Photoluminescent CdS Quantum Dots

“…Hot carrier transfer (vide infra) can play a significant role in such ultrafast quenching, which would not be reflected in nanosecond TCSPC transients and would lead to a considerable mismatch in Stern−Volmer plots constructed using PL intensities and lifetimes. 26,31,32 Hence, while a traditional Stern−Volmer analysis is less than adequate to explain the quenching mechanism, it provides important Ultrafast Transient Absorption: Hot Electron Transfer. A systematic investigation using transient absorption of QDs in the presence of varying concentration of Pb 2+ is performed to further elucidate the charge transfer process.…”

“…The nonlinearity of the Stern–Volmer plot and the excessively large value of k q indicates a close association of Pb 2+ ions with the QDs leading to “instantaneous” PL quenching post photoexcitation. Hot carrier transfer (vide infra) can play a significant role in such ultrafast quenching, which would not be reflected in nanosecond TCSPC transients and would lead to a considerable mismatch in Stern–Volmer plots constructed using PL intensities and lifetimes. ,, Hence, while a traditional Stern–Volmer analysis is less than adequate to explain the quenching mechanism, it provides important pointers, prompting a careful analysis of the femtosecond transient absorption data.…”

Felodipine Determination by a CdTe Quantum Dot-Based Fluorescent Probe

“…The colour of the solution immediately turned yellow, and the CdTe quantum dot precursor was obtained. The original solution was transferred to a hydrothermal synthesis reactor lined with Teflon and heated in an oven at 140 °C for different times to obtain transparent CdTe quantum dot solutions of different colours [ 25 , 26 ].…”