Research interests:
Donor-bridge-acceptor (D-B-A) assemblies with efficient long distance charge transport mechanisms are good candidates for potential photoconversion of solar energy. Optimization of these systems requires a fundamental understanding of the charge transfer process on the molecular level. The Wasielewski group has shown that energy level matching between the donor and bridge states in D-B-A molecules is required for wire-like charge transport across long bridge molecules to occur. While it has been suggested that structural dynamics play an important role in achieving wire-like transport, structural changes of the bridge during the charge transfer processes have not been probed directly with time-resolved methods.
I am interested in studying these bridge molecular structural dynamics coupled to charge transport in D-B-A molecules using a new vibrational spectroscopy technique, femtosecond time-resolved stimulated Raman spectroscopy (FSRS) (Figure 1). Unlike traditional time-resolved Raman spectroscopic techniques which are limited by the time-energy Fourier relationship, FSRS is capable of simultaneously achieving high spectral (~10 cm -1) and time (<100 fs) resolution.
The molecules currently under investigations contain a donor unit consisting of a 3,5-dimethyljulolidine molecule attached to anthracene (DMJ-A). Fluorenone (Fn) or Phenylene ethynyl (PE) units serve as the bridge to a naphthalenediimide (NI) acceptor. (Fig. 2) The FSRS spectra of DMJ-A-PE-NI have revealed the important vibrational modes associated with the charge transfer process (Fig. 3).
Figure 1. Femtosecond Stimulated Raman Spectroscopy
*McCamant, D.W.; Kukura, P.; Yoon, S.; Mathies, R.A. Rev. Sci. Inst.2004, 75, 4971-4981.
Figure 2. D-B-A molecules of interest: DMJ-A-B-NI where B is either phenylene ethynylene or fluorenone
Figure 3. FSRS spectra of DMJ-A-PE-NI
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