STUDY OF SUBSTITUENT EFFECTS ON THE PHOTOCONDUCTIVITY OF SOLUBLE 2,(3)-SUBSTITUTED AND 1,(4)-SUBSTITUTED PHTHALOCYANINATO-TITANIUM(IV) AND NAPHTHALOCYANINATOTITANIUM(IV) OXIDES

Soluble alkyl (II, 8a,b), fluoroalkyl,(4a), and fluoroalkoxy (4b,c, 8c ) 1,(4)- or 2,(3)-substituted phthalocyaninato- and linear 2,(3)- and- angular 1,(2)-annulated naphthalocyaninatotitanium(IV) oxides 10, 12, and 14 were synthesized and characterized with regard to their spectro scopic, photophysical, and photochemical properties. While alkyl- and fluoroalkoxy-substituted compounds are highly soluble in nonpolar solv ents, e.g., hexane, fluoroalkyl-substituted compounds are better solub le in polar aprotic solvents such as acetone. The stability against ph otooxidation in solution is' enhanced on going-from alkylated phthaloc yanines 1,(4)-(C5H11)(8)PcTiO (8a), 1,(4)-(C6H13)(8)PcTiO (4b), and 2, (3)-(C4H9)(8)PcTiO (II) to fluorinated phthalocyanines 2,(3)-(CF3)(4)P cTiO (4a), 2,(3)-(CF3CH2O)(4)PcTiO (4b), and 2,(3)-(CF3CH2O)(8)PcTiO ( 4c), from phthalocyanines to naphthalocyanines (tert-butyl)(4)-2,(3)-N cTiO (10), 1,(2)-NcTiO (12), and (tert-butyl)(4)-1,(2)-NdTiO (14), and on going from 2,(3)-substituted 4a-c to 1,(4)-substituted phthalocyan ines 8a-c. Thin films of these compounds, prepared by either vacuum de position or spin casting, are classified into three types according to increasing intermolecular pi-pi interactions. Type alpha films, chara cterized:by absence of exciton splitting, are formed from 1,(4)-substi tuted phthalocyanines 8a-c. These films show low dark conductivities a nd photoconductivities and are considerably sensitive to photooxidatio n. Type beta films, characterized by weak exciton splitting, are forme d from fluorinated phthalocyanines 4a-c as well as from rapidly deposi ted 2,(3)-substituted phthalocyanines II and the unsubstituted PcTiO ( I). These films show enhanced photoconductivity and are generally more stable against photooxidation than type alpha films. Type gamma films , formed by slow deposition of II, 10 and unsubstituted phthalocyanine I, are classified by a largely red-shifted B-band absorbing in the ne ar-IR. These films are highly photosensitive as well as stabilized aga inst photooxidation. Steady-state photoconductivities and dark conduct ivities in thin films are strongly dependent on oxygen partial pressur e. Alkylated PcTiO's such as 8a, 8b, and II are found to be p-type con ductors (positive oxygen influence on conductivities) like unsubstitut ed PcTiO (I), whereas angularly annulated naphthalocyanines such as 12 and 14 as well as fluorinated PcTiO's 4a-c are n-type conductors (neg ative oxygen influence on conductivity). These findings are rationaliz ed by comparison with experimental and theoretical literature data.