Femtosecond Transient Absorption (fsTA)

Transient absorption (TA) spectroscopy measures the evolution of the electronic absorption after a sample is excited.  During the experiment, a pump pulse is used to excite the sample, followed by a probe pulse at variable time delays, which for TA is a visible (400-750 nm) white light.  By measuring the transmission of the probe through the sample, it is possible to measure the decay of the excited state created by the pump pulse as a function of time.

The femtosecond broadband transient absorption (TA) system consists of an Astrella Titanium:Sapphire (Ti:Sapph) regenerative amplifier (Coherent, 1 kHz, 7 mJ, 35 fs, 800 nm).  The output is split into a pump and probe beam.  A small portion of the laser output is used to generate a white light continuum by focusing into a rotating CaF₂ crystal to create the probe beam.  Part of the remainder is sent to an optical parametric amplifier (Coherent, OPerA Solo) for the pump beam.  The OPerA Solo generate wavelengths from 325 to 2500 nm.  In the TA experiment, the probe is dispersed by a spectrograph (Horiba Triax, 550 mm fl, 150 grooves/mm) and measured by a CCD camera (Princeton Instruments Pixis 100F).  The broadband TA experiment requires transmissive sample, such as liquid or film.

Time-Resolved Infrared (TRIR)

Femtosecond time resolved infrared (TRIR), like TA, uses a pump pulse that to excite the sample.  The difference is that instead of a visible probe, the probe is in the IR electromagnetic range and is used to measure the decay in IR active vibrations in the sample.

The system consists of a Legend USP HE Ti:Sapp regenerative amplifier (Coherent, 1 kHz, 2.2 mJ, 35 fs, 800 nm).  This regenerative amplifier pumps two optical parametric amplifiers (Coherent, OPerA) with ~1 mJ each to generate pulses from 1150 to 2630 nm.  The output from one OPerA generates the pump beam for the TRIR experiment.  Nonlinear optics is used to create the ultraviolet and visible wavelengths for the pump, the OPerA output could under go harmonic generation (Coherent, UV/Vis module) or sum frequency mixing (Coherent, SFG module) for beams from 240-1150 nm.  The second OPerA generates the probe from 2400 to 10,000 nm using difference frequency mixing (Coherent, DFG module).  The probe is dispersed by a spectrograph (Horiba Triax 320 mm fl, 50 grooves/mm) and measured by a dual array MCT (InfraRed Associates).  TRIR requires transmissive sample, such as liquid or film.

Renishaw Raman IR Microprobe

This instrument is a combination of an inVia confocal Raman microscope for Raman spectroscopy and a Smiths Detection IlluminatIR II for FTIR.  The pump wavelengths for Raman spectroscopy available are 458, 514, 633 and 785 nm.  With the instrument configuration, it is able to record each spectrum individually or in combination to get a Raman spectra and FTIR on the exact same spot on the sample.  Samples can be film, powder, or liquid.  There is also a temperature cell available to use with films or powder that has a temperature range from -173 to 600 °C. 

Applied Photophysics SX-20 Stopped-Flow Spectrometer

• 20 µL Cell Volume with Dead Time of 1 ms
• Capable of Absorbance and Fluorescence Measurements
  • Absorbance: 185-900 nm
  • Fluorescence (Em): 300-650 nm
• Monochromator Slit Widths: 0.5-37 nm
• Xe Lamp Source
• Single-Mixing or Sequential-Mixing Modes Available
• Water Circulator Accessory for Controlled Temperature Experiments
• Anaerobic Adapter for Experiments in N₂ Environment

Coming soon: Polarized Raman Spectroscopy with the ability to change the polarization of the pump and/or probe for the 514, 633 ad 785 nm Raman pump wavelengths.

Select Publications - Femtosecond Transient Absorption (fsTA)

Loftus, L. M.; Rack, J. J.; Turro, C.; Photoinduced ligand dissociation follows reverse energy gap law: nitrile photodissociation from low energy ³MLCT excited states,  C. Chem. Commun., 2020, 56, 4070-4073.

Kender, W. T.; Turro, C.; Unusually Slow Internal Conversion in N-Heterocyclic Carbene/Carbanion Cyclometallated Ru(II) Complexes: A Hammett Relationship,  J. Phys. Chem. A, 2019, 123 (13), 2650-2660.

Whittemore, T. J.; Millet, A.; Sayre, H. J.; Xue, C.; Dolinar, B. S.; White, E. G.; Dunbar, K. R.; Turro, C.; Tunable Rh₂(II,II) Light Absorbers as Excited-State Electron Donors and Acceptors Accessible with Red/Near-Infrared Irradiation,  J. Am. Chem. Soc. 2018, 140, 5161-5170.

Select Publications - Time-Resolved Infrared (TRIR)

Xue, C.; Sayre, H. J.; Turro, C.; Electron injection into titanium dioxide by panchromatic dirhodium photosensitizers with low energy red light, Chem. Commun., 2019, 55, 10428-10431.

Kender, W. T.; Turro, C.; Unusually Slow Internal Conversion in N-Heterocyclic Carbene/Carbanion Cyclometallated Ru(II) Complexes: A Hammett Relationship, J. Phys. Chem. A, 2019, 123 (13), 2650-2660.

Whittemore, T. J.; White, T. A.; Turro, C.; New Ligand Design Provides Delocalization and Promotes Strong Absorption throughout the Visible Region in a Ru(II) Complex, J. Am. Chem. Soc. 2018, 140, 229-234.

Staff

Dr. Barbara Dunlap | Manager | 0103 Newman & Wolfrom Laboratory | 614-247-4754 | dunlap.300@osu.edu

Dr. Claudia Turro | Faculty Director | 4109 Newman & Wolfrom Laboratory | 614-292-6708 | turro@chemistry.ohio-state.edu