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

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 (Sigma_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 (Phi(HET)) of HET when CdTe QD-TCPP NCs are excited at higher excited state (similar to 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.

Automated summary

This study demonstrates hot electron transfer and ultrafast electron transfer between cadmium telluride quantum dots (CdTe QDs) and tetrakis(4-carboxyphenyl)porphyrin (TCPP) in newly prepared CdTe QD-tetrakis(4-carboxyphenyl)porphyrin nanocomposites (CdTe QD-TCPP NCs) using steady state, time-resolved emission, and femtosecond transient absorption spectroscopic techniques. The observation of efficient quenching of the photoluminescence of CdTe QDs with little change in photoluminescence decay profiles suggests a static interaction between CdTe QDs and TCPP. Excitation wavelength and intensity dependent studies confirm the hot electron transfer from higher excited states to TCPP, while ultrafast electron transfer from photoexcited TCPP to CdTe QDs is also observed.