Abstract

The nature and location of the triplet states of organic molecules has been of considerable interest for 40 years. Because of the metastable character of the lowest triplet (T₁) levels, it is possible to obtain a considerable population in T₁ by optical pumping. Transitions from this triplet to higher lying triplets may be induced by simultaneous excitation with a suitable probe source. Lewis and Lipkin were the first to observe triplet-triplet (T-T) absorption in an organic molecule. Since that time many investigators have successfully used the method to investigate excited triplet states. Two basic techniques for T-T absorption have been developed. In the first, introduced by McClure, steady-state illumination of the sample is used. The second, developed by Porter and co-workers, uses pulsed pump and probe radiation sources. By and large, in the great majority of reports on T-T absorption published to date, using either CW or pulsed techniques, the probe radiation has been confined to the visible and ultraviolet regions. These high probe energies ensure that only those excited triplets which lie at energies far removed from T₁ will be investigated. It is, however, generally expected that those triplets lying in closer proximity to T₁ will play a significant role in the mechanisms of nonradiative decay, photodegradation, etc., yet no systematic studies of T-T absorption in the infrared range have appeared. For a number of different classes of organic molecules (e.g., aromatic hydrocarbons and dicarbonyl compounds) there are theoretical predictions that one or more T-T transitions should lie in this range. To investigate these possibilities we have embarked on a program of T-T absorption in the infrared range using a Fourier transform (FT) IR spectrometer. In this note we report preliminary results on phenanthrene in a poly(methylmethacrylate) matrix that show that the application of an FT-IR spectrometer to T-T absorption measurements is feasible.

Mountaintop observation of CO₂ absorption spectra using a short wavelength infrared Fourier transform spectrometer

Yukio Yoshida, Hiroyuki Oguma, Isamu Morino, Hiroshi Suto, Akihiko Kuze, and Tatsuya Yokota
Appl. Opt. 49(1) 71-79 (2010)

High-resolution Fourier-transform cavity-enhanced absorption spectroscopy in the near-infrared using an incoherent broad-band light source

Johannes Orphal and Albert A. Ruth
Opt. Express 16(23) 19232-19243 (2008)

Multichannel Fourier-transform infrared spectrometer

Mamoru Hashimoto and Satoshi Kawata
Appl. Opt. 31(28) 6096-6101 (1992)

Infrared intracavity laser absorption spectroscopy with a continuous-scan Fourier-transform interferometer

Jixin Cheng, Hai Lin, Shuiming Hu, Shenggui He, Qingshi Zhu, and Alexander Kachanov
Appl. Opt. 39(13) 2221-2229 (2000)

Fourier-transform infrared imaging using a rapid-scan spectrometer

C. M. Snively, S. Katzenberger, G. Oskarsdottir, and J. Lauterbach
Opt. Lett. 24(24) 1841-1843 (1999)