A simple high-intensity UV-photon source for photochemical studies in UHV: Application to the photoconversion of norbornadiene to quadricyclane

Journal article


Publication Details

Author(s): Schwarz M, Schuschke C, Nascimento Silva T, Mohr S, Waidhas F, Brummel O, Libuda J
Journal: Review of Scientific Instruments
Publication year: 2019
Volume: 90
Journal issue: 2
ISSN: 0034-6748
eISSN: 1089-7623


Abstract

Photochemical in situ studies in a well-controlled surface science environment can help to understand photochemical reactions in organic thin films in more detail. To perform such studies without external focusing or light guiding systems, we designed a high-intensity UV-photon source, which is compatible with an ultra-high vacuum (UHV) environment. The UV source is based on a high power light-emitting diode (LED), soldered onto a copper heat reservoir to avoid overheating. The LED can be placed in close vicinity in front of a single crystal, providing flux densities of 2 x 10(18) photons s(-1) cm(-2) at a wavelength of 365 nm. Thus, the device provides light intensities one order of magnitude higher as compared to conventional continuous wave arc lamps, at only a small variation of the flux of less than +/- 20% over a sample surface of 10 x 8 mm(2). The UV source is mounted in a UHV infrared reflection absorption spectroscopy system and triggered by using the IR spectrometer. This allows fully automatized in situ IR studies of photochemical reactions at interfaces and thin films. We prove the functionality of the device by studying the photochemical conversion of norbornadiene (NBD) to quadricyclane (QC) mediated by the photosensitizer 4,4'-bis(dimethylamino) benzophenone (Michler's ketone, MK). NBD and MK were grown by physical vapor deposition in the form of thin films on Pt(111) at 120 K. Even at prolonged UV irradiation (>100 s), the temperature of the sample increased by less than 10 K. We report first successful conversion of NBD to QC under UHV conditions and follow the conversion behavior as a function of the photon dose and NBD/MK ratio. Initial quantum yields of up to 23% and selectivity for a QC of 70% are obtained at NBD/MK of 7.4:1, indicating good electronic coupling between NBD and MK even in a frozen multilayer. For both very small and very large NBD loadings, the conversion efficiency decreases, which is attributed to the effect of the metallic substrate and phase separation in thick multilayers, respectively. Published under license by AIP Publishing.


FAU Authors / FAU Editors

Brummel, Olaf Dr.
Lehrstuhl für Physikalische Chemie II
Libuda, Jörg Prof. Dr.
Professur für Physikalische Chemie
Mohr, Susanne
Lehrstuhl für Physikalische Chemie II
Nascimento Silva, Thais
Lehrstuhl für Physikalische Chemie II
Schuschke, Christian
Lehrstuhl für Physikalische Chemie II
Schwarz, Matthias
Lehrstuhl für Physikalische Chemie II
Waidhas, Fabian
Lehrstuhl für Physikalische Chemie II


How to cite

APA:
Schwarz, M., Schuschke, C., Nascimento Silva, T., Mohr, S., Waidhas, F., Brummel, O., & Libuda, J. (2019). A simple high-intensity UV-photon source for photochemical studies in UHV: Application to the photoconversion of norbornadiene to quadricyclane. Review of Scientific Instruments, 90(2). https://dx.doi.org/10.1063/1.5079320

MLA:
Schwarz, Matthias, et al. "A simple high-intensity UV-photon source for photochemical studies in UHV: Application to the photoconversion of norbornadiene to quadricyclane." Review of Scientific Instruments 90.2 (2019).

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Last updated on 2019-20-03 at 16:23