Comparative Photophysical Properties of Free-Base, Bis-Zn(II), Bis-Cu(II), and Bis-Co(II) Doubly N-Confused Hexaphyrins(1.1.1.1.1.1)

Abstract

We have comparatively investigated the photophysics of a series of bis-metal doubly N-confused hexaphyrins(1.1.1.1.1.1) using time-resolved fluorescence, femtosecond transient absorption, two-photon absorption measurements, and geometry-optimized ab initio calculations. Bis-Zn(II) and free-base doubly N-confused hexaphyrins exhibit well-resolved and red-shifted B- and Q-like absorption bands compared with porphyrins. Their allowed transitions are (pi,pi) transitions of the hexaphyrin ring, as confirmed by the HOMO and LUMO frontier orbitals based on ab initio calculations at the B3LYP/6-31G level. On the other hand, the absorption spectra of bis-Cu(II) and bis-Co(II) doubly N-confused hexaphyrins are relatively broad, presumably due to large couplings between the metal d-orbitals and pi-electrons of the hexaphyrin ring. Owing to these couplings, bis-Cu(II) and bis-Co(II) doubly N-confused hexaphyrins have much shorter excited-state lifetimes of 9.4 +/- 0.3 ps and 670 fs, respectively, than those (267 +/- 16 and 62.4 +/- 1.2 ps, respectively) of bis-Zn(II) and free-base doubly N-confused hexaphyrins. The two-photon absorption cross section (sigma(2)) values, which are believed to depend strongly on the ring planarity (pi-conjugation), are in line with the excited-state lifetime trends.

A Core‐Modified Rubyrin with meso‐Aryl Substituents and Phenanthrene‐Fused Pyrrole Rings: A Highly Conjugated Near‐Infrared Dye and Hg2+ Probe

“…However, the Stokes shift also suggests that the conformation of 1 deviates considerably from planarity because Stokes shifts of only 20-90 cm À1 have been reported for largely planar hexaphyrins. [8,26,27] This assumption is supported by the comparatively intense Q bands. When Q bands lose their ideal forbidden character, as in meso-substituted and anellated tetrapyrrole porphyrins that adopt a saddlelike conformation owing to internal steric strain, their intensity increases.…”

“…[5] Core-modified expanded porphyrins have been employed even less frequently, for example, thiophenemodified sapphyrins and rubyrins in anion-binding studies. [6] Although the cation-coordination chemistry of expanded porphyrins has been investigated, [7,8] reports on the use of such compounds in metal-ion sensing are even scarcer. [9] Based on our interest in the optical determination of heavy-metal ions, in particular of Hg 2+ , [10] and the development of new red/near-infrared (NIR) dyes, [11] we became intrigued by the possibility of equipping expanded porphyrins such as rubyrin, that is, [26]hexaphyrin(1.1.0.1.1.0), with various "soft" donor sites, [12][13][14] to shift metal-ion preferences from, for example, Zn 2+ , Cu 2+ , and Co 2+ in all-pyrrole derivatives [7] to more thiophilic target ions.…”

“…Despite the wealth of information available on the absorption properties of extended porphyrins, only few studies of their emission features have been published. [8,9,24,26,27] This can be explained by the difficulty of measuring emission spectra of compounds with low fluores- cence quantum yields-F f % 10 À4 have been reported [26,27] -at l em > 900 nm with conventional fluorometers. For the emission spectra shown in Figure 3, we used a different approach and employed an FTIR spectrometer equipped with a Nd:YAG laser and a photoluminescence detector operating in the conventional mode (see the Supporting Information for details).…”

Theoretical investigation of electronic structures and excitation energies of hexaphyrin and its group 11 transition metal (III) complexes

“…In recent years, considerable advancements have been made in expanded porphyrins that possess attractive photophysical, electronic and coordination properties which cannot be realized in normal porphyrin systems [1][2][3][4][5][6][7][8]. Expanded porphyrins including more than four pyrrole rings have been demonstrated to be quite promising due to their larger conjugation and structural diversity that allow remarkable absorption spectra ranging from the UV/ Visible to the near-IR region, variable oxidation states that are interconvertible among aromatic, antiaromatic, and nonaromatic compounds, and multi-metal coordinating behaviors.…”

Ein kernmodifiziertes Rubyrin mit meso‐Aryl‐Subsituenten und Phenanthren‐anellierten Pyrrolringen als hoch konjugierter NIR‐Farbstoff und Hg2+‐Sonde

“…[13] Um einen Farbstoff zu erhalten, der bei deutlich höheren Wellenlängen absorbiert, erwies sich die von uns kürzlich auf Tetrapyrrolporphyrine angewendete Anellierung von Phenanthrenringen an die bPyrrol-Position [25] [8,9,24,26,27] …”