Femtosecond time-resolved energy transfer from CdSe nanoparticles to phthalocyanines |
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Authors: | S Dayal R Królicki Y Lou X Qiu JC Berlin ME Kenney C Burda |
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Institution: | (1) Center for Chemical Dynamics and Nanomaterials Research, Department of Chemistry, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-7078, USA |
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Abstract: | The first real-time observation of the early events during energy transfer from a photoexcited CdSe nanoparticle to an attached
phthalocyanine molecule are presented in terms of a femtosecond spectroscopic pump–probe study of the energy transfer in conjugates
of CdSe nanoparticles (NPs) and silicon phthalocyanines (Pcs) with 120 fs time resolution. Four different silicon phthalocyanines
have been conjugated to CdSe NPs. All of these have proven potential for photodynamic therapy (PDT). In such NP-Pc conjugates
efficient energy transfer (ET) from CdSe NPs to Pcs occurs upon selective photoexcitation of the NP moiety. Spectral analysis
as well as time-resolved fluorescence up-conversion measurements revealed the structure and dynamics of the investigated conjugates.
Femtosecond transient differential absorption (TDA) spectroscopy was used for the investigation of the non-radiative carrier
and ET dynamics. The formation of excitons, trapped carriers states, as well as stimulated emission was monitored in the TDA
spectra and the corresponding lifetimes of these states were recorded. The time component for energy transfer was found to
be between 15 and 35 ps. The ET efficiencies are found to be 20-70% for the four Pc conjugates, according to fluorescence
quenching experiments. Moreover, as a result of the conjugation between NP and the Pcs the photoluminescence efficiency of
the Pc moieties in the conjugates do not strictly follow the quantum yields of the bare phthalocyanines.
PACS 73.63.Bd |
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