Octasubstituted phthalocyanines

They can be prepared from the respective 4-, 4,5- and 3-, 3,6-substituted phthalonitriles. Besides these most common tetra- and octasubstituted phthalocyanines, 1,3,8,10,15,17,22,24-octasub-stituted and 1,2,3,4,8,9,10.11,15,16.17,18,22,23,24,25-hexadecasubstituted phthalocyanines have been prepared.102... 

Little is reported about this substitution pattern. The 1,3,8,10,15,17,22,24-octasubstituted (1,3-octasubstituted) phthalocyanines are formed as structural isomers (see pp 736,737). 3,5-Dinitro-phthalonitrile (14) on heating at 180-190°C in nitrobenzene with a catalytic amount of ammonium molybdate(VI) affords phthalocyanine 15. 

The products are called 1,4-octasubstituted or 1,4,8,11,15,18,22,25-octasubstituted phthalocyanines. In this case only one structural isomer is possible. 3,6-Diheptylphthalonitrile when refluxed in pentan-1 -ol in the presence of nickel(II) acetate and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) for 48 hours yields the nickel phthalocyanine 16. 

The products are known as 2,3-octasubstituted or 2,3,9,10,16.17,23,24-octasubstituted phthalocyanines. As is the case for 1,4-octasubstituted phthalocyanines, only one structural isomer exists. Metal-free phthalocyanines 18 can be obtained by heating 4,5-disubstituted phthalonitriles 17 in a solvent containing a strong base such as l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Ammonia can also be used as a base. 

The products of the self-condensation by cyclization from 5,6-disubstituted isoindolinediimines are 2,3,9.10,16,17,23,24-octasubstituted phthalocyanines, e.g. 4. 

Octasubstituted phthalocyanines 8 are derived from the respective 3.6-di-substituted phthalonitriles 7. 

Phthalocyanines represent a class of inherently disc-like molecules and consequently were among some of the first examples of metallomesogens exhibiting columnar mesophases, being first reported by Simon and co-workers in 1982 [122]. Thus, they described an octasubstituted phthalocyanine copper(Il) complex (Figure 65) which exhibited a mesophase between 53°C and the start of decomposition at about 300°C X-ray diffraction studies showed lines with reciprocal spacing of 1 3 v 4 7,... 

Smolenyak PE, Peterson RA, Nebesny KW, Toiker M, O Brien DF, Armstrong NR (1999) Highly oidtaed thin films of octasubstituted phthalocyanines. J Am Chem Soc 121 8628— 8636... 

Di(trifluoroethoxy)phthalodinitrile 122 can be prepared from 2,3-dicyanohydroquinone 121 by alkylation with trifluoroethyltosylate in DMF [70], The 4,5-substituted dinitrile 125 is available from the 4,5-dibromocatechol 123 by consecutive alkylation with tosylate (DMF, K2CO3) and cyanation (CuCN, DMF) [70], 0=Ti" complexes of a- and p-octakis(trifluoroethoxy)phthalocyanines were prepared using these dinitriles 122 and 125 [70]. The Zn" complex of p-octasubstituted phthalocyanine was also reported [78],... 

Usually tetrasubstituted phthalocyanines (Fig. 15.4) show higher solubilities in organic solvents than the oc-tasubstituted ones (Fig. 15.5). There are mainly two reasons for this behavior The isomer mixture of four tetrasubstituted phthalocyanines leads to a lower order in the solid state compared to symmetrically octasubstituted phthalocyanines, and tetrasubstituted phthalocyanines possess a higher dipole moment caused by the unsym-metrical arrangement of the substituents in the periphery of the macrocycle. 

A particular attribute of octasubstituted phthalocyanines is their liquid crystalline behavior. Phthalocyanines substituted in peripheral positions by long-chain substituents form, depending on the structure (alkyl or alkoxy), liquid discotic (from the disclike shape of the molecules) crystalline phases [68-71 ] or columnar meso-phases [72]. Liquid crystalline phases are found for side chains longer than C4 or Q (depending on the metals and substituents used) [73]. In these mesophases the phthalocyanine moieties stack in columns with arrangements of different symmetry (Fig. 15.8), depending on the nature of the side chains [71,74]. Only chains connected with a heteroatom X (X = O, S) to the aromatic macrocycle show an arrangement with the molecular planes perpendicular to the column axis. 

Octasubstituted phthalocyanines are symmetrical when both the substituents are the same and are prepared from homogeneously disubstituted phthalonitriles containing the same substituents. Unsymmetrically octasubstituted phthalocyanines are obtained from heterogeneous disubstituted phthalonitriles having different substituents. The same principle can be extended to deca- and hexadeca-substituted phthalocyanines. Unsymmetrical phthalocyanines with different substituents in one or two benzene ring can be synthesized starting from two differently substituted phthalocyanines. This will afford a mixture of unsymmetrically substituted phthalocyanines, which have to be separated by chromatography (see below). 

A particular attribute of octasubstituted phthalocyanines is their liquid crystalline behavior. Phthalocyanines substituted in peripheral positions by long chain substituents form, depending upon the structure (alkyl or alkoxy), liquid discotic (from the disc-like shape of... 

In contrast to tetrasubstituted and octasubstituted phthalocyanines, reports on phthalocyanines with lower symmetry have rarely appeared, mainly because of the problems associated with the separation of isomers during preparation [85,86]. Phthalocyanines with lower symmetry show interesting non-linear optical properties... 

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