Evanescent Wave Excited Fluorescence from Self-Assembled Phthalocyanine Monolayers

Abstract

Novel phthalocyanine (Pc) molecules have been designed and synthesized to incorporate a thiol moiety for the formation of monolayer films onto gold-coated optical waveguides via the technique of self-assembly. The thiol moiety is connected to the Pc macrocycle by either a (CH2)11 or (CH2)3 hydrocarbon chain. Both Pc SAMs have been characterized on the metal surface using reflection absorption infrared (RAIR) spectroscopy. The RAIR spectra suggest that the two Pc molecules lie in a different orientation with respect to the gold surface. This behavior can be rationalized with consideration of the different structures (the different alkyl connecting chain lengths and different macrocyclic peripheral side chains) of the two Pc molecules. The fluorescence emission spectrum of each of the Pc SAMs has been obtained by exciting each monolayer along the longitudinal axis of the optical waveguide via laser-induced evanescent wave stimulation. The use of the longer mercaptoalkyl connecting chain appears to inhibit quenching of the electronically excited state through energy transfer to the metal layer. It is thought that the presence of peripheral alkyl side chains (six hexyl or seven decyl chains, respectively) minimizes self-quenching in the single-component SAM film. It has also been shown that the fluorescence signal of the (CH2)11 mercaptoalkyl Pc SAM can be reversibly quenched by exposure to gaseous nitrogen dioxide (NO2). The decrease in fluorescence intensity has been related to increasing NO2 concentration by a Stern−Volmer relationship. The Pc SAM can detect concentrations of NO2 down to 10 ppmv with no interferent effect seen from other environmentally relevant gases: carbon monoxide and carbon dioxide. These results suggest that SAMs of specifically designed materials, such as Pc's, may be used as sensitive receptor molecules to form the basis of a novel technology for the development of optical chemical sensors for gaseous species.

Novel optical NO2-selective sensor based on phthalocyaninato-iron(II) incorporated into a nanostructured matrix

“…In order to develop NO 2 -sensors based on MP, the following gas-permeable supports were used: (1) pre-cleaned glass slides [14]; (2) gold-coated optical waveguides [24]; (3) tinmodified mesoporous silica [25]; (4) SnO 2 [26]; (5) porous silicon [27]; etc. A variety of techniques such us vacuum sublimation, plasma-activated evaporation, solvent evaporation from a fine suspension, spin-coating, Langmuir-Blodgett and self-assembly deposition were used to produce these sensors.…”

Catalytic Oxidative Polymerization of Vinyl Monomers Using Cobalt Phthalocyanine Complex and an Exploratory Investigation on the Polymerization of Vinyl Acetate

“…Since its discovery, metal phthalocyanines have become one of the most important candidates for numerous applications such as electrophotography, optical data storage systems, chemical sensors, photovoltaic cells, fuel cells, electronic devices, photodynamic therapy of cancer, self-assembled monolayers and oxidation of organic compounds. [7][8][9][10][11][12][13][14][15] This is the first report on the oxidative polymerization of vinyl monomers, which has been achieved at low temperatures. When a homogeneous solution of a vinyl monomer containing a reversible oxygen carrier, namely cobalt(II) phthalocyanine pyridine complex [Co II Pc(Py)], is exposed to oxygen, an alternating copolyperoxide is obtained (eq 1).…”

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

“…Compounds of series 3 also form LB films but also act as precursors to series 4 [24]. The latter form selfassembled monolayer (SAM) films on gold slides [25,26]. Reflection-absorption infrared spectroscopy (RAIRS) indicates that the angle between the plane of the ring and the substrate surface increases as the length of the tethering chain is increased from (CH 2 ) 3 through (CH 2 ) 8 to (CH 2 ) 11 [27].…”