Monolayer behaviour and Langmuir–Blodgett film properties of some amphiphilic phthalocyanines: factors influencing molecular organisation within the film assembly

Abstract

The monolayer and LB film-forming properties of 20 structurally related amphiphilic octa-substituted phthalocyanine derivatives have been assessed. The molecular packing within examples of the films has been probed by visible-region spectroscopy and low-angle X-ray diffraction methods. Among derivatives where the aliphatic substituents are attached by ether linkages, there is a variation in the behaviour according to the length of the chains and whether or not the chains are branched. Films are not highly ordered but may contain domains of ordered structure, giving rise to r i redshifted absorption band in the visible spectrum. Analogues where the chains are attached by carbon-carbon bonds show superior monolayer behaviour and are excellent materials for deposition as LB films. Furthermore, there is good evidence from the spectra that change in the length of the alkyl chains provides a means of controlling the type of molecular packing within the films.

Tuning the arrangement of mono-crown ether-substituted phthalocyanines in Langmuir–Blodgett films by the length of alkyl chains and the cation in subphase

“…These can be ascribed to exciton coupling between the neighboring molecules. In most of the cases, the LB film of phthalocyanine showed either red-shifted or blue-shifted absorption peaks, but Cook's and other groups discovered another aggregation behavior, which gives splitting Q bands (Davydov splitting) for octasubstituted phthalocyanines with long alkyl chains [18,19]. Cook's results tell us that in a nonperipheral unsymmetrically octasubstituted phthalocyanine, when the alkyl chains are longer than six carbons, the film shows a split Q band while a shorter substitution (such as n-C 6 H 13 or iso-C 5 H 11 ) group presents normal red-shifted spectra.…”

Non-uniformly substituted phthalocyanines and related compounds: alkylated tribenzo-imidazolo[4,5]- porphyrazines

“…These films are well ordered as judged from X-ray reflectivity measurements, with the molecules deposited anisotropically as shown from polarized light absorption spectroscopy, polarized FTIR spectroscopy [15] and by AFM [21]. The last of these techniques provides compelling evidence for the presence of very long columnar assemblies of molecules within a molecular layer, with the column axes aligned preferentially along the dipping direction.…”

“…The presence of alkyl (or alkoxy) groups in the non-peripheral (a) positions on three of the four benzenoid rings of the Pc ring systems, as in 1, 2 and 3, confers solubility in organic solvents, and we find that there is less tendency for aggregation in the solution phase than when the same groups are at the peripheral sites. The alkoxy groups in particular at the non-peripheral sites lead to a significant bathochromic shift of the Q band [15]. Pcs bearing alkyl groups exhibit interesting discotic mesophase behaviour [16][17][18].…”

“…The 3:1 Pcs of series 1 and 2 are ideal materials for depositing as Langmuir-Blodgett (LB) films [15,19,20]. These films are well ordered as judged from X-ray reflectivity measurements, with the molecules deposited anisotropically as shown from polarized light absorption spectroscopy, polarized FTIR spectroscopy [15] and by AFM [21].…”

Electrochemical characterisation of tetra- and octa-substituted oxo(phthalocyaninato)titanium(IV) complexes

“…Substitution at this more sterically crowded nonperipheral position also reduces aggregation tendencies more than substitution at the peripheral position [29][30][31][32][33]. Introduction of different kinds of substituents onto the periphery and changing the central metal can alter spectroscopic and electrochemical properties.…”