nach oben

Erschienen in:

2015 | OriginalPaper | Buchkapitel

2. “Prototypical” Optical Absorption Spectra of Phthalocyanines and Their Theoretical Background

verfasst von : Hiroaki Isago

Erschienen in: Optical Spectra of Phthalocyanines and Related Compounds

Verlag: Springer Japan

Einloggen

Aktivieren Sie unsere intelligente Suche, um passende Fachinhalte oder Patente zu finden.

search-config

KI-gestützte Suche

Aus

Abstract

In this chapter the prototypical optical absorption spectra of metal-free and metallated phthalocyanines and their theoretical background on the basis of some simple molecular orbital (MO) models are described. Comparison of these spectra with those of porphyrins and other related macrocycles with the tetrapyrrol skeleton suggests that (1) the electronic structures of phthalocyanines are similar to those of porphyrins and (2) the structure of their innermost 16-membered ring is very important for understanding their spectra. Starting from the simplest MO model (a “free electron” circulating along the periphery of an ideal cyclic polyene, C₁₆H ₁₆ ^2- ), the well-known “four-orbital model” is derived without extreme mathematicization but as graphically as possible. The four-orbital model predicts that doubly degenerate LUMOs (lowest unoccupied molecular orbital; e_g) and two nearly degenerate HOMOs (highest occupied molecular orbital; a_1u and a_2u) play a crucial role in determining the spectra of porphyrins and related macrocycles. The appearance of an intense Q band in the spectra of phthalocyanines is interpreted in terms of the disruption of the near degeneracy of the HOMOs. This is due to a higher stability of an a_2u orbital than of the a_1u counterpart owing to the presence of nitrogen atoms at meso-positions. Magnetic circular dichroism spectroscopy is briefly introduced as a powerful tool to investigate degenerate electronic structures of compounds of high symmetry such as porphyrins and phthalocyanines.

Sie haben noch keine Lizenz? Dann Informieren Sie sich jetzt über unsere Produkte:

Springer Professional "Wirtschaft+Technik"

Online-Abonnement

Mit Springer Professional "Wirtschaft+Technik" erhalten Sie Zugriff auf:

über 102.000 Bücher
über 537 Zeitschriften

aus folgenden Fachgebieten:

Automobil + Motoren
Bauwesen + Immobilien
Business IT + Informatik
Elektrotechnik + Elektronik
Energie + Nachhaltigkeit
Finance + Banking
Management + Führung
Marketing + Vertrieb
Maschinenbau + Werkstoffe
Versicherung + Risiko

Jetzt Wissensvorsprung sichern!

Jetzt informieren

Springer Professional "Technik"

Online-Abonnement

Mit Springer Professional "Technik" erhalten Sie Zugriff auf:

über 67.000 Bücher
über 390 Zeitschriften

aus folgenden Fachgebieten:

Automobil + Motoren
Bauwesen + Immobilien
Business IT + Informatik
Elektrotechnik + Elektronik
Energie + Nachhaltigkeit
Maschinenbau + Werkstoffe

Jetzt Wissensvorsprung sichern!

Jetzt informieren

Vorheriges Kapitel Introduction

Nächstes Kapitel Real Optical Absorption Spectra Observed in Laboratories

The “tbpc” is the abbreviation of tetra(tert-butyl)phthalocyaninate dianion (Sect. 1.2.2).

Careful readers may be concerned that the tetrasubstituted phthalocyanines are mixtures of four regioisomers, as determined from the positions of the substituents. This is true. However, it is not important in most cases. One research group has successfully separated four regioisomers of tetrasubstituted phthalocyanines using an HPLC technique; however, they have determined that the difference in their spectral properties is negligible [1].

The split Soret and Q bands of H₂tbpc are attributed to the symmetry-lowering effect based on the presence of imino protons in the cavity, as described in Sect. 2.2.9.

In this subsection, as the central elements do not play a crucial role, they are not specified in the abbreviations of the macrocyclic compounds.

The peripheral substituents are omitted for clarity in this discussion.

In contrast, disruption of the π-conjugation system in the innermost 16-membered ring of phthalocyaninate leads to the disappearance of the characteristic Q band (one or more broad bands are observed in the 400–500 nm region, instead) [4].

Refer to Sect. 1.1.4 for the definitions of HOMO and LUMO.

Even though there seems to be no red or blue color between neighboring atoms, it may be assumed that a considerable amount of π-cloud is present when the atoms have the same sign (color).

Note that a nodal plane is present on the molecular plane (because of the nature of the p_z orbital) but this is not taken into account here.

Note that all the ethylene moieties are isolated from the innermost 16-membered ring in a_2u by nodes.

In general, irreducible representations starting with a capital letter stand for a “state”, whereas those starting with a small letter represent MOs.

This description is rather qualitative and oversimplified. The MO wave function shown in Figs. 2.7 and 2.8 are converted by linear combinations of their complex forms (Eq. 2.7). Readers who are interested in strict, quantitative derivation should refer to the original papers [6‐9].

For some compounds, e.g., [Zn(pc)], [Mg(pc)], [Li₂(pc)] [19‐21], and some As^V and Sb^V derivatives [22‐24], a similar absorption band in the spectral region has been reported but they are considered as an overlap of two bands (B1/B2 bands) on the basis of MCD spectra (Sect. 3.2.2.1).

With respect to the second vibronic band (612 nm), Mack and Stillman have suggested the presence of an additional nondegenerate electronic (n-π) transition in this spectral region due to the lack of the corresponding band in the fluorescence spectrum [25].

The convention employed for D_2h here is different from that of the global standard, which recommends taking the z-axis (principal axis) in the D_2h point group so that it passes through as many atoms as possible (i.e., the z-axis is parallel to the phthalocyanine molecular plane). This is the reason why some studies have shown that the split LUMOs belong to b_1g and b_2g. However, strictly following the standard convention might lead to unnecessary confusion in comparison with [Zn(Pc)] (D_4h), where the z-axis must be its C₄ axis and hence is perpendicular to the molecular plane. Therefore, the z-axis for H₂Pc has been taken similarly for easier comparison with [Zn(Pc)].

M. Sommerauer, C. Rager, M. Hanack, J. Am. Chem. Soc. 118, 10085–10093 (1996)CrossRef

O.S. Finikova, A.V. Cheprakov, I.P. Beletskaya, P.J. Carroll, S.A. Vinogradov, J. Org. Chem. 69, 522–535 (2004)CrossRef

E.S. Nyman, P.H. Hynninen, J. Photochem. Photobiol. B Biol. 73, 1–28 (2004)CrossRef

C. Ercolani, A.M. Paoletti, G. Pannesi, G. Rossi, A. Chiesi-Villa, C. Rizzoni, J. Chem. Soc. Dalton Trans. 1971–1977 (1990)

W.T. Simpson, J. Chem. Phys. 17, 1218–1221 (1949)CrossRef

A. Ceulemans, W. Oldenhof, C. Görller-Walrand, L.G. Vanquickenborne, J. Am. Chem. Soc. 108, 1155–1163 (1986)CrossRef

M. Gouterman, J. Mol. Spectrosc. 6, 138–163 (1961)CrossRef

M. Gouterman, G.H. Wagniere, L.C. Snyder, J. Mol. Spectrosc. 11, 108–127 (1963)CrossRef

C. Weiss, H. Kobayashi, M. Gouterman, J. Mol. Spectrosc. 16, 415–450 (1965)CrossRef

10.

M.J. Stillman, T. Nyokong, in Phthalocyanines: Properties and Applications, vol. 1, ed. by C.C. Leznoff, A.B.P. Lever (VCH, New York, 1989), p. 133

11.

J. Mack, M.J. Stillman, in Porphyrin Handbook, vol. 16, ed. by K.M. Kadish, K.M. Smith, R. Guilard (Elsevier Science, USA, 2003), pp. 43–116CrossRef

12.

J. Mack, M.J. Stillman, Coord. Chem. Rev. 219–221, 993–1032 (2001)CrossRef

13.

J. Mack, M.J. Stillman, J. Am. Chem. Soc. 116, 1292–1304 (1994)CrossRef

14.

J. Mack, S. Kirkby, E. Ough, M.J. Stillman, Inorg. Chem. 31, 1717–1719 (1991)CrossRef

15.

J. Mack, M.J. Stillman, Inorg. Chem. 36, 413–425 (1997)CrossRef

16.

J. Michl, J. Am. Chem. Soc. 100, 6801–6811 (1978)CrossRef

17.

J. Michl, Tetrahedron 40, 3845–3934 (1984)CrossRef

18.

J.H. Dawson, J.R. Trudell, G. Barth, R.E. Linder, E. Bunnenberg, C. Djerassi, M. Gouterman, C.R. Connell, P. Sayer, J. Am. Chem. Soc. 99, 641–642 (1977)CrossRef

19.

E. Ough, T. Nyokong, K.A.M. Creber, M.J. Stillman, Inorg. Chem. 27, 2724–2732 (1988)CrossRef

20.

M.J. Stillman, A.J. Thomson, J. Chem. Soc. Faraday Trans. II(70), 805–814 (1974)CrossRef

21.

T.C. VanCott, J.L. Rose, G.C. Misener, B.E. Williamson, A.E. Schrimph, M.E. Boyle, P.N. Schatz, J. Phys. Chem. 93, 2999–3011 (1989)CrossRef

22.

H. Isago, Y. Kagaya, Inorg. Chem. 51, 8447–8454 (2012)CrossRef

23.

H. Isago, Y. Kagaya, J. Porphyrins Phthalocyanines 13, 382–389 (2009)CrossRef

24.

H. Isago, Y. Kagaya, H. Fujita, T. Sugimori, Dyes Pigm 88, 187–194 (2010)

25.

J. Mack, M.J. Stillman, J. Phys. Chem. 99, 7935–7945 (1995)CrossRef

26.

N. Kobayashi, H. Konami, in Phthalocyanines: Properties and Applications, vol. 4, ed. by C.C. Leznoff, A.B.P. Lever (VCH, New York, 1996), p. 343

Titel: “Prototypical” Optical Absorption Spectra of Phthalocyanines and Their Theoretical Background
verfasst von: Hiroaki Isago
Verlag: Springer Japan
Buch: Optical Spectra of Phthalocyanines and Related Compounds
Print ISBN: 978-4-431-55101-0

Electronic ISBN: 978-4-431-55102-7

Copyright-Jahr: 2015
DOI: https://doi.org/10.1007/978-4-431-55102-7_2

Premium Partner

Marktübersichten

Die im Laufe eines Jahres in der „adhäsion“ veröffentlichten Marktübersichten helfen Anwendern verschiedenster Branchen, sich einen gezielten Überblick über Lieferantenangebote zu verschaffen.

Zur Marktübersicht