This paper reviews the studies on the electronic structures and spectroscopic properties of sandwich-type complexes M ( Pc )2 and M 2( Pc )3. The subjects discussed are as follows. (1) Electronic spectra of closed-shell Pc dimers and trimers. The complexes with closed-shell systems, such as [ Lu ( Pc )2]−, Sn ( Pc )2 and Lu 2( Pc )3, can be thought of as stacked systems composed only of Pc 2−. The excited states of these complexes can be described by locally excited and charge transfer configurations. The coupling terms of the configurations are written using orbitals localized on each Pc ring. Assignments of the observed absorption bands are discussed. Computational studies on the band assignments were carried out using a localized molecular orbital (LO) basis which maximizes orbital populations on one of the Pc rings. (2) Electronic structures of πelectron-deficient Pc dimers and trimers. Oxidation of [ Lu ( Pc )2]− or Lu 2( Pc )3 yields systems with π-electron deficiency or π-hole(s) residing on multiple Pc sites. The delocalized nature of the π-hole in Lu ( Pc )2 is elucidated by comparison of the electronic spectra of symmetric and asymmetric dimers composed of Pc and Nc ( H 2 Nc ≡ naphthalocyanine ). The band assignments of the dimer radicals are discussed. The Pc trimer radical shows an intense absorption band at about 5000 cm−1, which is 2000 cm−1 lower than the valence resonance band of Lu ( Pc )2. The two-electron-deficient complexes [ Lu ( Pc )2]+ and [ Lu 2( Pc )3]2+ also show intense near-IR bands at higher energy than the corresponding monoradical species. The interactions that determine the excitation energies of the near-IR bands of the π-electron-deficient species are elucidated.
AIE/ACQ Effects in Two DR/NIR Emitters: A Structural and DFT Comparative Analysis