Porphyrins are one of the most important biological molecules essential for life and responsible in nature for such oxidation-reduction reactions as photosynthesis in plants and respiration in animals. Synthetic porphyrins have broad applications as useful opto-electronic materials in different fields of organoelectronics, such as solar cells, photodetectors, and as catalysts in a variety of reactions. Advantages of using porphyrins as opto-electronic materials include efficiency of charge separation and charge transport even in thick films of assembled porphyrins, strong absorbance in the visible region, high chemical stability, and ability to tune optoelectronic properties. However, there are some problems associated with application of porphyrins in organoelectronics. Porphyrins have a modest spectral overlap with solar spectrum and the material preparation and isolation is difficult. Additionally, fluorescence of porphyrinoids in the near infrared (NIR) is quite rare. For a number of potential optoelectronic applications strong absorption in NIR spectral region is desired. One of the approaches to get absorption in NIR spectral region is by extending the size of π-conjugation in the porphyrin system. The conjugation of porphyrins can be extended through several modes of substitution involving the (meso), (β,β), (β,meso) and (β,meso, β) positions. It has been shown previously that some aromatic rings can be fused with porphyrins in (β,meso) and (β,meso, β) modes. These reactions require activation of porphyrin rings by metalation with nickel(II) or activation of aromatic rings by multiple alkoxy-substitution. Nickel(II) porphyrins have rapid decay of the excited state due to nickel centered (d,d) quenching and at the same time demetalation of such porphyrins does not have synthetic potential since it requires harsh conditions not suitable with the presence of alkoxy groups (for example, concentrated sulfuric acid). Nickel(II) porphyrinoids have not found any applications in photovoltaics and no emission has been reported for such porphyrins containing nickel atom or donor alkoxy groups. Additionally, this usually causes difficulties with synthesis, and isolation is possible only in small amounts. One of the most limiting factors in use in organoelectronics of many derivatives of porphyrins with extended conjugation is both their very low solubility and inability to sublime.
Almost all porphyrins, phthalocyanines and subphthalocyanines have a metal or heteroatom in the center. The ability of metals to coordinate with different ligands may provide a new way to tune properties of macrocycles and, thus, enhance organoelectronic device performance. Literature data shows that at least for some systems consisting of macrocycles such supramolecular organization through coordination by metal centers can enhance conductivity and charge transport. Although coordination chemistry of metalated macrocycles are very well established, application of this strategy to change and improve optoelectronic devices with use of such macrocycles as porphyrins, phthalocyanines, etc. still remains unrealized.
USPTO Backgrounds
USPTO Backgrounds