1. Field of the Invention
The present invention relates generally to ionic conjugated polymers. More specifically, the present invention applies to fluorescent ionic conjugated polymers complexed with oppositely charged surfactants to form a polymer-surfactant complex characterized by enhanced photophysical properties and to methods of producing the same.
2. Description of Related Art
Polymers enjoy an expanding range of applications. Conjugated polymers have been widely recognized for their potential as inexpensive and versatile electronic materials for many applications. Because of their wide-ranging applicability, major efforts have been focused on determining the relationship between the polymer chemical structure and conformation and the corresponding physical and chemical properties of polymer materials. Common efforts have focused on altering polymer properties by modifying the polymer conformation through changes in the polymer/monomer design and through synthesis steps that change the conjugated repeat units of the polymer.
For example, the fluorescence emission wavelength may be tuned over the entire visible range to obtain variable-color LEDs by varying polymer substituent groups to tune the xcfx80-electron density. The fluorescence can be further tuned over an additional 100 nm by varying the repeat unit to construct polymers with varying degrees of rigidity. These methods also affect the conductivity and quantum efficiency of fluorescent polymers. One of the most challenging aspects of these prior art methods is that a polymer""s properties are altered by changing the repeat unit conformation of that polymer. This means that a new polymer must be synthesized for each desired variation of the polymer""s electronic or photophysical properties.
For example, polymers with desired physical properties often lacked desired photophysical properties, and the desired physical properties were often lost when a new polymer was synthesized to have improved photophysical properties. Existing and newly discovered polymers with desired physical properties were rarely adapted for use in fluorescent or luminescent devices because the necessary synthesis steps often resulted in entirely different polymers that lacked either the desired physical or photophysical properties.
From the foregoing, a person having ordinary skill in the art will appreciate that there is a need in the art for ionic conjugated polymers in which the fluorescence and photophysics may be easily altered or enhanced without formidable synthesis steps. It would be a further advancement to provide a fluorescent conjugated polymer complex that exhibits enhanced photophysical properties. It would also be a significant advancement to provide a technique for enhancing a conjugated ionic polymer""s fluorescence and photophysics that does not require challenging synthetic efforts. Hence, a simple technique to enhance fluorescent ionic conjugated polymer""s photophysical properties without the need to synthesize new chemical structures would be extremely desirable.
Such complexes and techniques for their formation are disclosed and claimed herein.
The present invention is drawn to novel ionic conjugated polymer complexes characterized by enhanced photophysical properties. The present invention includes a fluorescent polymer-surfactant complex with at least one improved photophysical property such as increased quantum efficiency, excitation wavelength independent emissions spectra, narrowed and red-shifted absorption spectra, or reduction of non-radiative fluorescent decay pathways. These improvements are accomplished by complexing a fluorescent ionic conjugated polymer with an effective amount of an oppositely charged surfactant in a polar solvent.
The polymer-surfactant complexes within the scope of the present invention that exhibit enhanced photophysical properties may be easily prepared. They are prepared by adding an effective amount of oppositely charged surfactant to a solution of fluorescent ionic conjugated polymer in polar solvent.
By way of example and not by limitation, the complexes within the scope of this invention may exhibit increased fluorescence quantum efficiency compared to the neat polymer with a ratio of surfactant molecule to monomer repeat unit of polymer of just 1:100. Fluorescence emissions are generally amplified with increased surfactant concentration up to the point of surfactant saturation.
The polymer-surfactant complexes within the scope of the present invention may exhibit many other improved photophysical properties; the properties and the degree of improvement may vary depending on the polymer and surfactant used to form the complex. These complexes may exhibit fluorescence quantum efficiency improvement by a factor ranging from 2 to 20, or more, when compared to the neat polymer. Complexes within the scope of the present invention may have emission spectra that are excitation wavelength independent. They may have absorption spectra that are narrowed and red-shifted when compared to the neat polymer. The fluorescence of the polymer-surfactant complexes may also be characterized by single exponential decay kinetics rather than the less stable, multi-exponential decay characteristic of neat polymers.
Persons having ordinary skill in the art will appreciate that the polymer-surfactant complexes within the scope of this invention are valuable due to their potential to exhibit increased stability, increased fluorescence intensity, and increased control over fluorescent emissions. The value of these complexes is further increased because they are easy to prepare. The preparation of polymer-surfactant complexes within the scope of the present invention is very flexible allowing them to be used in a variety of applications.
One may prepare complexes within the scope of the present invention by adding an effective amount of surfactant to a solution of fluorescent ionic conjugated polymer. The surfactant and polymer solution concentrations can be varied to achieve desired photophysical properties. Typically, one polymer is complexed with one surfactant, but mixtures of multiple polymers and multiple surfactants may be used. Polymer-surfactant complexes of the present invention are commonly prepared in a polar solvent or mixture of solvents, though they may be prepared in any inert solvent chemically compatible with the ionic polymer and surfactant.
One may prepare complexes within the scope of the present invention by adding a sufficient amount of surfactant to a polymer solution to create a polymer-surfactant complex precipitate. Polymer-surfactant complex precipitates exhibit one or more of the improved photophysical properties discussed above. They are useful in a number of solid-state forms, primarily as thin films.
Additional features of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the invention. The features of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.