Low Temperature Physics: 36, 451 (2010); https://doi.org/10.1063/1.3432263 (7 pages)
Физика Низких Температур: Том 36, Выпуск 5 (Май 2010), c. 563-570 ( к оглавлению , назад )
Unveiled optical properties of tetrapyrollic pigments in cryogenic environments
C. Crépin, N. Shafizadeh, and W. Chin
Institut des Sciences Moléculaires d’Orsay, Bât. 210
Laboratoire Aimé Cotton, Bât. 505 CNRS & Université Paris-Sud 11, 91405 Orsay cedex, France
Department of Chemistry, National University of Ireland, Maynooth, Ireland
Belarusian State Agrarian and Technical University, Minsk, Belarus
Received February 15, 2010
An unexpected phenomenon was revealed in the laser induced fluorescence spectra of free-base (H2Pc) and zinc (ZnPc) phthalocyanines trapped in rare gas and nitrogen matrices under a moderate increase in the laser intensity. In all matrices the intensity of an emission band near 755 nm increased drastically when pumping the S1 ← S0 transition. This observation was assigned to stimulated emission in a four-level scheme involving a vibronic transition from the lowest electronic state to a vibrational level of the ground state. In the present work, we expose new similar results obtained with porphyrin molecules, i.e. tetra-benzoporphin (TBP). With free-base H2TBP, stimulated emission was observed in Ar or N2 matrices, but not in Xe matrices. A possible reason could be a fast inter-system crossing rate due to the heavy atom effect induced by Xe. We also report the observation of persistent burnt spectral holes, although the low efficiency of this process is not competitive with stimulated emission and no decrease of the stimulated emission with time was observed. With ZnTBP, no stimulated emission could be recorded; however the appearance of rather strong phosphorescence was noticed. Similar studies focusing on the stimulated emission phenomenon is that they should allow new insights into site effects and site selectivity.
PACS: 33.50.–j Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion);
Key words: tetrabenzoporphin, cryogenic matrices, stimulated emission, fluorescence, phosphorescence, spectral hole-burning.