A Structural Isomer of Nonaromatic Porphyrin:  Preparation of 20π-Conjugated Porphycene Based on Electronic Perturbation

Abstract

A porphycene having four CF3 groups at the beta-pyrrolic positions affords a stable 20pi-conjugated form in the presence of a 2H+-2e- donor due to the high redox potential of the tetrapyrrole ring framework. No visible band in the UV-vis spectrum and the highly ruffled structure determined by X-ray crystallography support its nonaromatic character. The ethylene bridge moiety in the 20pi-conjugated framework displayed the olefinic reactivities.

Investigation of Aromaticity and Photophysical Properties in [18]/[20]π Porphycene Derivatives

“…[25] Whereas the optimized molecular structure of [18]EtioPc reveals a quite planar geometry, [18]CF 3 Pc shows a slightly ruffled structure due to the steric/electronic repulsion between bulky trifluoromethyl substituents (Figure 1). Furthermore, [20] [20] Although the MOs of [18]CF 3 Pc also show a quite similar behavior to [18]EtioPc, the energy stabilization of LUMO was observed due to the existence of electron-withdrawing substituents (Figure 2). This feature is in good accordance with the previously reported electrochemical observation of [18]CF 3 Pc.…”

“…Chen et al [16] reported in 2007 that trifluoromethyl groups on pyrrole rings give rise to relatively air-stable [20]p porphyrin. After this work, Hayashi et al [17] also reported the successful synthesis and isolation of air-stable [20]p b-tetrakis(trifluoromethyl) porphycene ( [20]CF 3 Pc) through two-electron reduction and two protonation processes of [18]p b-tetrakis (trifluoromethyl)porphycene ([18]CF 3 Pc), which seems to be an analogue of etioporphycene ( [18]EtioPc) (Scheme 1). [18,19] Porphycene, the first porphyrin isomer, was synthesized by Vogel and co-workers in 1986, and a considerable number of research efforts have been conducted on novel synthesis, characterization, and applications of various porphycene derivatives over the past few decades.…”

“…After this work, Hayashi et al [17] also reported the successful synthesis and isolation of air-stable [20]p b-tetrakis(trifluoromethyl) porphycene ( [20]CF 3 Pc) through two-electron reduction and two protonation processes of [18]p b-tetrakis (trifluoromethyl)porphycene ([18]CF 3 Pc), which seems to be an analogue of etioporphycene ( [18]EtioPc) (Scheme 1). [18,19] Porphycene, the first porphyrin isomer, was synthesized by Vogel and co-workers in 1986, and a considerable number of research efforts have been conducted on novel synthesis, characterization, and applications of various porphycene derivatives over the past few decades. [20,21] In particular, over the last decade, the photophysical properties of [4n+2]p porphycenes such as NH tautomerization, [21] singlemolecule imaging, [22] nonlinear optical (NLO) properties, [23] and conical intersection process [24] have been studied.…”

“…In this regard, we have investigated the relationship between aromaticity and photophysical properties of [18]/ [20]p porphycenes by using theoretical calculations and spectroscopic methodologies. This is, to the best of our knowledge, Abstract: In this study, we have investigated the relationship between aromaticity and photophysical properties of trifluoromethyl-substituted [18]/ [20]p porphycenes by using theoretical calculations and various spectroscopic methodologies.…”

“…This is, to the best of our knowledge, Abstract: In this study, we have investigated the relationship between aromaticity and photophysical properties of trifluoromethyl-substituted [18]/ [20]p porphycenes by using theoretical calculations and various spectroscopic methodologies. Interestingly, we have found that the HOMO-LUMO gap of [20]p porphycene is larger than that of [18]p porphycene, which is in a sharp contrast with those of typical …”