Formation and spectroscopic characterisation of self-assembled phthalocyanine monolayers

Abstract

A series of three Phthalocyanine (Pc) derivatives have been designed, synthesised and formulated as selfassembled monolayers (SAMs) on gold-coated optical waveguides. The alkyl chain tethering the Pc macrocycles to the gold surface via a thiol moiety varied in length viz. (CH 2 ) 11 , (CH 2 ) 8 and (CH 2 ) 3 . The three Pc SAMs have been characterised using re¯ection absorption infrared spectroscopy and ¯uorescence spectroscopy excited via the evanescent wave. The infrared data have shown that the length of the alkyl tether has a profound effect on the orientation and packing density of the Pc macrocycle on the gold surface. Similarly, the intensity of ¯uorescence observed from the Pc monolayers was related to the length of the alkyl tether. A further investigation of the C 11 Pc derivative SAM has shown that the monolayer ®lm was stable, exhibiting no oxidation and only minor orientation changes on the gold surface over a period of 24 months as determined by infrared and ¯uorescence spectroscopy. The longevity of the Pc SAM is thought to be due to the macrocyclic ring possibly preventing oxidation of the thiolate root. As simple alkanethiols are known to oxidise at gold surfaces, the stability results obtained for the Pc derivative would suggest that macrocyclic SAMs may have properties that are more suitable for long term applications.

Surface electrochemistry of iron phthalocyanine axially ligated to 4-mercaptopyridine self-assembled monolayers at gold electrode: Applications to electrocatalytic oxidation and detection of thiocyanate

“…This process is of vital importance for improving the reliability of the results. The reason for the good stability shown by this SAM may be related to the protection of the sulphur by the macrocyclic ring of the phthalocyanine as suggested by other studies [54,55]. The interchain attractive interactions resulting from the pyridine moiety may also be a contributing factor to the stability.…”

Electrochemical and photophysical characterization of non-peripherally-octaalkyl substituted dichlorotin(IV) phthalocyanine and tetrabenzotriazaporphyrin compounds

“…Substitution at the more sterically crowded α (non-peripheral) positions with, for example, alkyl groups, reduces aggregation tendencies and enhances solubility in non-polar solvents more so than substitution at β (peripheral) positions. It also results in enhanced red shifting of the Q-band of the Pc complexes [12][13][14][15][16][17][18]. Various examples of both non-peripherally and peripherally octa-substituted Pcs exhibit liquid crystal behavior [19][20][21].…”

Voltammetric characterisation of the self-assembled monolayers (SAMs) of benzyl- and dodecyl-mercapto tetra substituted metallophthalocyanines complexes

“…Thiol derivatised metallophthalocyanine SAMs have been shown to have their sulphur group protected by the phthalocyanine ring thereby increasing their stability [26]. Investigation of the influence of a long alkyl chain on the formation and stability of thiol derivatised metallophthalocyanine SAMs should therefore be of great interest.…”