DEVELOPMENT OF VISIBLE, NEAR-INFRARED, AND MID-INFRARED TRANSIENT ABSORPTION SPECTROSCOPY ON A FEMTOSECOND TO MILLISECOND TIMESCALE AND ITS APPLICABILITY TO ORGANIC ELECTRONIC MATERIALS
Open Access
- Author:
- Rimshaw, Adam
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 31, 2016
- Committee Members:
- John B Asbury, Dissertation Advisor/Co-Advisor
John B Asbury, Committee Chair/Co-Chair
Mark Maroncelli, Committee Member
Benjamin James Lear, Committee Member
Enrique Daniel Gomez, Outside Member - Keywords:
- Ultrafast Spectroscopy
Nanosecond Spectroscopy
Organic Photovoltaics
Organic Solar Cells - Abstract:
- Nanosecond transient absorption instruments capable of 10-5 sensitivity were developed for visible, near-infrared, and mid-infrared spectral regions. These instruments were developed around new advances in analogue to digital (ADC) conversion called flexible resolution. Unlike the traditional ADC architecture, which interleaves multiple 8-bit ADCs to achieve higher resolution, the digitizers used within this manuscript allows multiple high-resolution ADCs to be applied to the input channels in different time-interleaved and parallel combinations to boost either the sampling rate or the resolution. The result is instrumentation capable of changing resolution (8-14 bit), which helps to increase the signal-to-noise ratio by more than an order of magnitude. For each instrument, the spectral and temporal range is explored with an emphasis on the sensitivity and collection time. The detection limit of both nanosecond instruments was calculated to be 10-5 O.D. Example materials were studied on both nanosecond instruments to show their capability in real-world applications with systems such as P3HT:PCBM, CN-MEH-PPV and TIPS-pentacene. The mid-IR instrument provided some of most sensitivity spectra ever recorded in the mid-IR, such as alkyne stretches measuring < 100 μO.D. in TIPS-pentacene films on a nanosecond timescale. The ability to record such data within a reasonable time frame makes possible for significantly lower energy densities to be used in studying organic electronic materials. Our ultrafast laser system was expanded to perform visible pump―visible pump spectroscopy and our preexisting visible pump―mid-IR pump was redesigned with new technologies such as remote connectivity. All of the instrument’s programming was redone using MATLAB―streamlining our data collection and analysis. Important advances were made in terms of data acquisition time and statistical filtering using the new software as well. The redesigned system allowed us to start exploring perylene diimide solutions for unique vibrational modes due to excimer formation. Lastly, these advances have opened the door to developing a new kind of ultrafast technique termed pump-push-probe, which allows for photophysics to be studied on functioning organic electronic devices.