A. J. de Mello

PHTHALOCYANINE FLUORESCENCE AT HIGH CONCENTRATION: DIMERS OR REABSORPTION EFFECT?

Abstract— For tetrasulfonated aluminum phthalocyanine (AlPcS4), dimer formation is characterized in the absorption spectrum by a broadening of the Q‐band and the appearance of a new band at the red edge of the spectrum. The high concentrations required to produce dimers, however, often leads to anomalous observations in fluorescence spectroscopy. In the present study, we have examined the photophysical characteristics of two dye systems; AlPcS4 in a 66% ethanol/water mixture and disulfonated aluminum phthalocyanine in methanol. Using absorption spectroscopy, the formation of dimers is shown to be prevalent only in the case of AlPcS4. The fluorescence emission spectra in both cases, however, exhibit similar spectral changes with increasing dye concentration. The measured fluorescence decay profiles for both dyes also show similar trends: They are monoexponential, invariant with emission wavelength and have decay times that increase with dye concentration. These distortions are sometimes incorrectly attributed to dimer fluorescence. We find no evidence for the existence of dimer fluorescence and demonstrate that these data can be readily explained, by taking into consideration the effects of reabsorption of fluorescence.

Influence of thermal treatment on the conductivity and morphology of PEDOT/PSS films

Abstract The electrical properties of conducting polymers are strongly dependent on their film morphology and chemical and physical structure, which in turn can be strongly modified via a variety of post-deposition treatments. The aqueous dispersion of poly(3,4-ethylenedioxythiophene) with polyelectrolyte, poly(styrene sulfonic acid) (PEDOT/PSS) was used as the conducting polymer in our study. We report an investigation of the conductivity and morphology of spin-coated films and their dependence on heat treatment procedures in both air and N 2 atmospheres.

Patterning of organic devices by interlayer lithography

We report a new lithographic procedure that enables the patterning of as-received semiconducting polymers and small molecules at the near micron level without causing discernible degradation of the patterned material. The method involves a minimum of processing steps, requires no modification of the active layer, and is compatible with both rigid and flexible substrates. The technique makes use of an intermediate resist layer between the substrate and the active layer, i.e.underneath the active layer, and involves the simultaneous patterning of the resist and active layers in a single expose/develop step. The technique has been successfully applied to the fabrication of flexible ITO-free light-emitting diodes and photodiodes, yielding peak quantum efficiencies of 8.8 cd A−1 and 57% respectively comparable to similar devices fabricated on ITO-coated glass. It is also readily extendible to the patterning on a single substrate of multiple devices incorporating different component materials, e.g. the red, green and blue pixels of a colour display.

A high-pressure interconnect for chemical microsystem applications

A PEEK interface for use in microfluidic applications is designed, fabricated and tested. The interface allows for the facile, non-permanent coupling of standard capillary tubing to silicon/glass micromixer chips. Importantly, the interface provides for a secure connection between capillary lines and chip reservoirs without the need for any adhesive materials. Furthermore, when used in conjunction with silicon/glass micromixer chips fluidic transport is stable over a wide range of volumetric flow rates (1-1500 microL min(-1)), and the entire construct can be rapidly assembled and disassembled at any time during the course of experimentation.