Novel insights on the vibronic transitions in free base meso-tetrapyridyl porphyrin

J M S Lopes; K Sharma; R N Sampaio; A A Batista; A S Ito; A E H Machado; P T Araújo; N M Barbosa Neto

doi:10.1016/j.saa.2018.10.054

Novel insights on the vibronic transitions in free base meso-tetrapyridyl porphyrin

Spectrochim Acta A Mol Biomol Spectrosc. 2019 Feb 15:209:274-279. doi: 10.1016/j.saa.2018.10.054. Epub 2018 Oct 31.

Authors

J M S Lopes¹, K Sharma², R N Sampaio³, A A Batista⁴, A S Ito⁵, A E H Machado⁶, P T Araújo⁷, N M Barbosa Neto⁸

Affiliations

¹ Institute of Natural Sciences, Graduate Program in Physics, Federal University of Pará, Belém, PA, Brazil. Electronic address: lopesjefferson01@yahoo.com.br.
² Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL, United States; Center of Materials for Information Technology (MINT Center) University of Alabama, Tuscaloosa, AL, United States.
³ Department of Chemistry, The University of North Carolina at Chapel Hill, Murray Hall, Chapel Hill, NC, United States.
⁴ Department of Chemistry, Federal University of São Carlos, São Carlos, SP, Brazil.
⁵ College of Philosophy, Sciences, and Letters of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil.
⁶ Institute of Chemistry, Federal University of Uberlândia, Uberlândia, MG, Brazil; Special Academic Unit of Physics, Graduate Program in Exact and Technological Sciences, Federal University of Catalão, Catalão, Goiás, Brazil.
⁷ Institute of Natural Sciences, Graduate Program in Physics, Federal University of Pará, Belém, PA, Brazil; Department of Physics and Astronomy, University of Alabama, Tuscaloosa, AL, United States; Center of Materials for Information Technology (MINT Center) University of Alabama, Tuscaloosa, AL, United States. Electronic address: paulo.t.araujo@ua.edu.
⁸ Institute of Natural Sciences, Graduate Program in Physics, Federal University of Pará, Belém, PA, Brazil. Electronic address: newtonfisico@gmail.com.

PMID: 30414576
DOI: 10.1016/j.saa.2018.10.054

Abstract

We present novel results on the free base 5,10,15,20-meso-tetra(pyridyl)-21H,23H-porphyrin (H₂TPyP). This molecule presents complex electronic and vibrational properties and despite the vast literature reporting the transitions observed in its absorption and fluorescence spectra, a more accurate interpretation has been kept elusive. In particular, we show that the molecule's Q-band develops into many electronic and vibronic transitions, whose the well-known "four orbital model" finds it difficult to reconcile. Using distinct spectroscopy techniques, we conclude that both Q_x- and Q_y-bands comprise, in fact, two quasi-degenerated electronic states together with their respective vibronic progressions each. The analysis of the Huang-Rhys factors and complementary time- and polarization-resolved measurements reinforce the need for the proposed Q-band multi features remodeling.

Keywords: Huang-Rhys Factor; Multiple vibronic transitions; Porphyrins.