The Alpha Substitution Effect on Phthalocyanine Aggregation

Abstract

<jats:p> The dimerization and tendency to form higher aggregates of two isomeric metal-free phthalocyanine compounds with tetracumylphenoxy peripheral substitution at the alpha (1 or 4, 5 or 8, 9 or 12, 13 or 16) and beta (2 or 3, 6 or 7, 10 or 11, 14 or 15) positions has been analysed by spectroscopic measurements. The dimerization constants in chloroform solution are 1.3 × 10<jats:sup>1</jats:sup> M <jats:sup>−1</jats:sup> and 7.0 × 10<jats:sup>3</jats:sup> M <jats:sup>−1</jats:sup> respectively. At concentrations greater than 10<jats:sup>−3</jats:sup> M , the beta phthalocyanine isomer forms a spectroscopically resolvable higher aggregate. Q-band spectra of the dimer of each isomer and of the aggregate of the beta isomer in chloroform solution were generated. Comparison of these spectra with the corresponding thin film spectra of each isomer indicates that the stronger tendency toward aggregation of the beta isomer extends into the solid state. The difference in aggregating tendency of the two isomers was attributed to a steric constraint of the alpha isomer that restricts conformational freedom and, consequently, hinders formation of dimer and higher order complexes. </jats:p>

Oligooxyethylene liquid phthalocyanines

“…The thin film spectra of the b-and asubstituted phthalocyanines are broadened and blue-shifted as a result of aggregation. The effect is smaller for the asubstituted phthalocyanine as previously observed in the cumylphenoxy phthalocyanine analog [13]. The spectrum of the octa-a-substituted phthalocyanine film is broadened and more red-shifted.…”

“…This hypothesis led to the approach of selecting ethylene oxide oligomer peripheral substituents for the phthalocyanine ring with the objective of rendering the phthalocyanine molecule an isotropic liquid at room temperature. It was also decided to investigate peripheral substitution at the more sterically restricted a position [10][11][12], since, in comparison with the b position, substitution at the a position reduces aggregating tendency [13]. This approach has been successful in generating optically clear, intrinsically liquid phthalocyanines which can be processed into thin film cells by capillary action, and optical limiting results on these materials were reported 3 years ago [14,15].…”

Synthesis and Characterization of Soluble Chloro- and Aryl(naphthalocyaninato)indium(III) Complexes and Their Precursors

“…Aggregation can strongly influence the NLO properties. [12] In phthalocyanines without an axial ligand, such as tetrakis(cumylphenoxy)-substituted phthalocyanines, there are pronounced spectral changes at higher concentrations, such as a substantial absorption band shift of several nm for the 2,(3)-substituted isomer, and a peak extinction change of about an order of magnitude. Higher solubility in thin liquid and solid films, in comparison to that of the axially halogen-substituted species, is even observed.…”

Synthesis and properties of novel polymeric metal-free and metallophthalocyanines containing peripherally long 1,2-bis[(3-oxapropyl)oxa]benzene derivatives

“…Figure 3e shows a broader absorbance at the concentrations corresponding to the large decrease in monomer extinction coefficient at 709 nm, indicating the appearance of species with overlapping. 53 Absorbance versus concentration graphs were examined to determine whether compounds 4-8 obey the Lambert-Beer law or not (Figures 2a-2e). In Figure 2e, a deviation from the Lambert-Beer law for 4 was observed at the studied concentrations due to the deprotonation of 4 at high pyridine concentrations.…”