Journal of Porphyrins and Phthalocyanines J. Porphyrins Phthalocyanines 2013; 17: 489–500 DOI: 10.1142/S1088424613500259 Published at http://www.worldscinet.com/jpp/ Copyright © 2013 World Scientific Publishing Company INTRODUCTION In recent years, there has been considerable interest in the synthesis and properties of planar binuclear phthalocyanines due to their potential use in non- linear optical [1] and data storage devices, and as laser dyes [2]. Intense absorption has been reported in the near IR-region for planar binuclear phthalocyanines with a shared benzene ring [3]. There is a 200 nm red shift of the Q band relative to the corresponding phthalocyanine monomer, due to the extension of the π-conjugation system. This makes these compounds potentially suitable for use as solid and liquid phase color filters as well as IR-region labels. The first attempt to increase the size of the aromatic bridge from benzene to naphthalene was reported by Yang et al. [2]. However, the target compound was obtained in only 6% yield and the optical properties in the near IR-region were not reported. In subsequent research, the data obtained were somewhat contradictory [1, 2, 4]. The Moscow group recently reported the synthesis in high yield of peripherally alkyl- and phenyl- substituted coplanar binuclear phthalocyanines sharing a common naphthalene ring [5, 6] and examined their electrochemical, spectroelectrochemical and physico- chemical properties [5, 6]. In this paper, magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations are used to further analyze the electronic MCD spectroscopy and TD-DFT calculations of a naphthalene-ring-bridged coplanar binuclear phthalocyanine dimer John Mack a,b◊ , Xu Liang a , Tatiana V. Dubinina c , Larisa G. Tomilova c , Tebello Nyokong b◊ and Nagao Kobayashi* a◊ a Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan b Department of Chemistry, Rhodes University, Grahamstown 6140, South Africa c Chemistry Department, M.V. Lomonosov Moscow State University, 1 Leninskie Gory, 119991 Moscow, Russia Dedicated to Professor Özer Bekaroğlu on the occasion of his 80th birthday Received 27 January 2013 Accepted 27 February 2013 ABSTRACT: Magnetic circular dichroism (MCD) spectroscopy and TD-DFT calculations are used to analyze the electronic structure and optical properties of an alkyl-substituted naphthalene-ring-bridged coplanar binuclear phthalocyanine dimer. An analysis of the MCD spectrum of the naphthalene-ring- bridged dimer relative to those of benzene-bridged compounds reported previously, demonstrates that there is a significantly weaker interaction between the two phthalocyanine rings. TD-DFT results obtained using the B3LYP functional with 6–31G basis sets were found to be problematic. Closer agreement with the experimental data is obtained when the CAM-B3LYP functional is used instead. The naphthalene- ring-bridged compound is found to be unsuitable for use as a photosensitizer for the formation of singlet oxygen, because the Φ T values are negligible. KEYWORDS: phthalocyanine, MCD spectrocopy, TD-DFT calculations. ◊ SPP full member in good standing *Correspondence to: Nagao Kobayashi, email: nagaok@m. tohoku.ac.jp, fax: +81 22-795-7719