Study of Substituent Effects on the Photoconductivity of Soluble 2,(3)- and 1,(4)-Substituted Phthalocyaninato- and Naphthalocyaninatotitanium(IV) Oxides

Abstract

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 spectroscopic, photophysical, and photochemical properties. While alkyl- and fluoroalkoxy-substituted compounds are highly soluble in nonpolar solvents, e.g., hexane, fluoroalkyl-substituted compounds are better soluble in polar aprotic solvents such as acetone. The stability against photooxidation in solution is enhanced on going from alkylated phthalocyanines 1,(4)-(C5H11)8PcTiO (8a), 1,(4)-(C6H13)8PcTiO (8b), and 2,(3)-(C4H9)8PcTiO (II) to fluorinated phthalocyanines 2,(3)-(CF3)4PcTiO (4a), 2,(3)-(CF3CH2O)4PcTiO (4b), and 2,(3)-(CF3CH2O)8PcTiO (4c), from phthalocyanines to naphthalocyanines (tert-butyl)4-2,(3)-NcTiO (10), 1,(2)-NcTiO (12), and (tert-butyl)4-1,(2)-NcTiO (14), and on going from 2,(3)-substituted 4a−c to 1,(4)-substituted phthalocyanines 8a−c. Thin films of these compounds, prepared by either vacuum deposition or spin casting, are classified into three types according to increasing intermolecular π−π interactions. Type α films, characterized by absence of exciton splitting, are formed from 1,(4)-substituted phthalocyanines 8a−c. These films show low dark conductivities and photoconductivities and are considerably sensitive to photooxidation. Type β films, characterized by weak exciton splitting, are formed from fluorinated phthalocyanines 4a−c as well as from rapidly deposited 2,(3)-substituted phthalocyanines II and the unsubstituted PcTiO (I). These films show enhanced photoconductivity and are generally more stable against photooxidation than type α films. Type γ films, formed by slow deposition of II, 10 and unsubstituted phthalocyanine I, are classified by a largely red-shifted B-band absorbing in the near-IR. These films are highly photosensitive as well as stabilized against photooxidation. Steady-state photoconductivities and dark conductivities in thin films are strongly dependent on oxygen partial pressure. Alkylated PcTiO's such as 8a, 8b, and II are found to be p-type conductors (positive oxygen influence on conductivities) like unsubstituted PcTiO (I), whereas angularly annulated naphthalocyanines such as 12 and 14 as well as fluorinated PcTiO's 4a−c are n-type conductors (negative oxygen influence on conductivity). These findings are rationalized by comparison with experimental and theoretical literature data.

Free-base tetra-arylphthalocyanines for dye-sensitised nanostructured solar cell applications

“…7), a weak band at $681 nm and a shoulder at $622 nm are observed (trace b). This is very similar to what is reported in the literature for Pc-Ti(O) [29]. The absorption spectrum of the electrolyte (Fig.…”

Tetrakis‐phthalocyanines bearing electron‐withdrawing fluoro functionality: Synthesis, spectroscopy, and electrochemistry

“…Electron-withdrawing substituents at the periphery of the macrocycle cause a large increase in the ionization potential of the system, protect the MPc from oxidative destruction [15][16][17], and thus enhance its catalytic activity. From the viewpoint of organic semiconductors, it is known that substitution of electron donor and acceptor groups leads to p-type and n-type characteristics of the Pc ring, respectively [7,[18][19][20].…”

Synthesis of a Bisphthalocyanine and Its Nonlinear Optical Properties

“…The binuclear complex displayed a positive nonlinear absorption coefficient. It is found that the linear optical properties were little changed but the optical limiting effectiveness of the binuclear fused phthalocyanine 1 is lower relative to tBu 4 The versatility of Pc synthetic organic chemistry [21,22] has led to a large variety of Pc structures differing in the number, nature and position of peripheral substituents, [23][24][25][26][27] with various coordinating central atoms, [17] axial ligands, [28,29] and with a variable number of linkages between Pc rings in oligomeric [30,31] or polymeric species. [32] Among the many possibilities for varying the Pc structure, the expansion of the π-electron system through the synthesis of naphthalocyanines (Ncs) is the most common.…”