j. phys. chem. lett., 2010, 1, 215-218
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DESCRIPTIONJ. Phys. Chem. Lett., 2010, 1, 215-218. Introduction. 3,5-dimethyl-4-(9-anthracenyl)julolidine. Electron transfer (ET) processes and charge transfer (CT) states are involved in photosynthesis utilized in opto-electronic devices - PowerPoint PPT Presentation
J. Phys. Chem. Lett., 2010, 1, 215-218
IntroductionElectron transfer (ET) processes and charge transfer (CT) states are involved in photosynthesis utilized in opto-electronic devicesElectron donor acceptor (DA) molecules are useful for studying fundamental processes associated with electron transfer reactionsCT states can be a mixture of locally excited (LE) and radical ion pair (RP; D+-A-) statesControlled by solvent polarityDMJ-An is an exampleMethyl groups inhibit rotation and simplify photophysicsFemtosecond Stimulated Raman Spectroscopy (FSRS) to probe the extent of charge separation in the CT state.
FSRS: Basic PrinciplesRev. Sci. Instrum., Vol. 75, No. 11, 2004, 4971-4980Annu. Rev. Phys. Chem., 2007, 58, 461 88.
LASER system and Experimental Setup
Annu. Rev. Phys. Chem., 2007, 58, 461 88.FSRS: Advantages
FSRS: Fluorescence Rejection
DMJ-An: Electronic Spectroscopylex = 400 nmAn-DMJ+DMJ-AnCT SimAn3,5-dimethyl-4-(9-anthracenyl)julolidineRoom Temperature Spectra in THF, ex(TA) = 400 nm
FSRS Spectrum (ex = 400 nm, Raman = 800 nm, Room Temperature, THF)Anthracene localized vibrations (*) Resonance enhancementJulolidine localized vibrations (*)Compare to 9-phenylanthracene (PA)PA contains localized An VibrationsDMJ-An CT excited state most closely resembles the PA- radical anion DMJ-An: FSRS Results
FSRS: Basic PrinciplesRev. Sci. Instrum., Vol. 75, No. 11, 2004, 4971-4980
Figure 1. Schematic layout of a grating-based compressor with negative dispersion, i.e. the short wavelengths (in blue) come out first. http://en.wikipedia.org/wiki/Chirped_pulse_amplification#With_gratings
Coherent Anti-stokes Raman SpectroscopyIncreases the intensity of the anti-stokes transitions relative to spontaneous anit-stokes radiation
IR Vibrational Echo Experiments
I chose this paper for the opportunity to describe FSRS, which is the system currently being build in the CCBD lab, in some detail. The DA molecule of this study then provides an example molecule to interpret typical FSRS spectra.800 nm output is frequency doubled to produce the actinic pump pulse (ground state excitation).White light continuum produced by sapphire disk (SD)How is raman pump generated? Check rev. sci. instrum. papers.Vibrational time scales can range from ~ 10 500 fs. Also, chemical reactions generally occur along a vibrational coordinate. Vibrational spectroscopy can be a direct probe of chemical reaction dynamics.
Molecular vibrational frequencies have large sensitivity to even very small changes in geometric structure (hundredths of angstrom changes in bond lengths) and therefore vibrational spectroscopy has potential as a direct probe for reaction dynamics.
This technique offers both enhanced time-resolution into the femtosecond realm as well as spectral range and resolution throughout the infrared spectrum.
Impulsive raman: higher time resolution, but limited spectral range.Ground state abs (inset)Excited state abs (main spectrum)Review ground state and excited state raman (b). Talk about the 3 types of pulses in FSRS (c). Talk about stimulated raman (a) and how it removes fluorescence background by taking the ratio of the actinic pump on to the actinic pump of conditions.
The raman probe spectrum helps eliminate fluorescence?
Pulses 1 and 3 determine the time resolution. Pulse 2 determines the spectral resolution.
Gain: Raman Pump on/off. Actinic and Raman probe on during both conditions. (if the actinic pump is off when the raman pump is on you get the ground state gain spectrum)