page_title: Phthalocyanine
section_title: Properties
hierarchical_section_title: Phthalocyanine / Properties
caption_attribution_description: Top panels: experimental STM images of one molecule adsorbed at an off-center pore site obtained by different bias potentials. Left Vb = −2 eV, middle Vb = −1 eV, right Vb = +1 eV. Bottom panels: simulated STM images of the offA1 optimized structure, also obtained with the same three bias potentials.
context_page_description: Phthalocyanine is a large, aromatic, macrocyclic, organic compound with the formula (C₈H₄N₂)₄H₂ and is of theoretical or specialized interest. It is composed of four isoindole units linked by nitrogen atoms. H₂Pc has a two-dimensional geometry and a ring system consisting of 18 π-electrons. The extensive delocalization of the π-electrons affords the molecule useful properties, lending itself to applications in dyes and pigments. Metal complexes derived from Pc²⁻
  , the conjugate base of H₂Pc, are valuable in catalysis, organic solar cells, and photodynamic therapy.
context_section_description: Phthalocyanine and derived metal complexes (MPc) tend to aggregate and, thus, have low solubility in common solvents. Benzene at 40 °C dissolves less than a milligram of H
  ₂Pc or CuPc per litre. H
  ₂Pc and CuPc dissolve easily in sulfuric acid due to the protonation of the nitrogen atoms bridging the pyrrole rings. Many phthalocyanine compounds are, thermally, very stable and do not melt but can be sublimed. CuPc sublimes at above 500 °C under inert gases (nitrogen, CO
  ₂). Substituted phthalocyanine complexes often have much higher solubility. They are less thermally stable and often can not be sublimed. Unsubstituted phthalocyanines strongly absorb light between 600 and 700 nm, thus these materials are blue or green. Substitution can shift the absorption towards longer wavelengths, changing color from pure blue to green to colorless (when the absorption is in the near infrared).
  There are many derivatives of the parent phthalocyanine, where either carbon atoms of the macrocycle are exchanged for nitrogen atoms or the peripheral hydrogen atoms are substituted by functional groups like halogens, hydroxyl, amine, alkyl, aryl, thiol, alkoxy and nitrosyl groups. These modifications allow for the tuning of the electrochemical properties of the molecule such as absorption and emission wavelengths and conductance.
caption: STM images of individual phthalocyanine molecules recorded at a bias of −2 V (left) and +1 V (right). Note that STM probes density of electrons in the HOMO/LUMO bands rather than atomic profiles.[2]
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