Analysis on high-resolution spectrum of the S1-S0 transition of free-base phthalocyanine

Yuki Miyamoto; Ayami Hiramoto; Kana Iwakuni; Susumu Kuma; Katsunari Enomoto; Naofumi Nakayama; Masaaki Baba

doi:10.1063/5.0191810

Analysis on high-resolution spectrum of the S1-S0 transition of free-base phthalocyanine

J Chem Phys. 2024 Apr 14;160(14):144304. doi: 10.1063/5.0191810.

Authors

Yuki Miyamoto¹, Ayami Hiramoto¹, Kana Iwakuni², Susumu Kuma³, Katsunari Enomoto⁴, Naofumi Nakayama⁵, Masaaki Baba^{6

7}

Affiliations

¹ Research Institute for Interdisciplinary Science, Okayama University, Kita-ku, Okayama 700-8530, Japan.
² Institute for Laser Science, University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.
³ Atomic, Molecular and Optical Physics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
⁴ Department of Physics, University of Toyama, Toyama 930-8555, Japan.
⁵ CONFLEX Corporation, 3-23-17 Takanawa, Minato-ku, Tokyo 108-0074, Japan.
⁶ Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan.
⁷ Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

PMID: 38591681
DOI: 10.1063/5.0191810

Abstract

A high-resolution absorption spectrum of the S1-S0 transition of free-base phthalocyanine was observed and analyzed with improved reliability. The spectrum, with a partially resolved rotational structure, was obtained by using the buffer-gas cooling technique and a single-mode tunable laser. Our new analysis reveals that the S1←S0000 band belongs to the a-type transition, where the electronic transition moment aligns parallel to the NH-HN direction, allowing the assignment of the S1 state to 1B3u. These results agree with a prior study using supersonic expansion and are well supported by theoretical calculations. Interestingly, the rotational constant B in the S1 state, which is often smaller than that in the ground state for typical molecules, was found to be slightly larger than that in the S01Ag state. This suggests a change in the character of π bonds with the electronic excitation.