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PRF Annual Report

We have continued to characterize the sensitivity of spectroscopic shifts of three organic dyes in response to their chemical environment.  Specifically, this year we studied methyl yellow and derivatives of Brooker’s merocyanine.  Our approach has been to dissolve each dye in dozens of pure solvents and record their absorbance spectra.  We then correlate the frequency of maximum absorbance or fluorescence (ν_max) with the solvent parameters π*, α, β, and δ.  These parameters measure a solvent’s dipolarity/polarizability, hydrogen bond (HB) donating ability, HB accepting ability, and excess polarizability.  These correlations take the form

 ν_max = πp* + aα + bβ+ dδ + ν_o

 The provisional coefficients obtained for absorbance measurements made on methyl yellow and a derivative of Brooker’s merocyanine are found in the table below.  Uncertainties are shown in parentheses. 

The results for methyl yellow indicate that the dye’s frequency of maximum absorbance depends primarily on the polarity of the solvent with little to no influence from solvent hydrogen bond donating or accepting ability.  The results for the merocyanine indicate that solvent polarity and hydrogen bond donating ability both play major roles in determining the frequency of maximum absorbance.  Given the structure of the merocyanine (see ‘nugget’), this is not surprising as it is a polar molecules with a prominent hydrogen bond accepting site.  Interactions with that site will clearly alter the ground and excited states of the dye and thus its absorbance properties.  With several such dyes of varying dependence, it should be possible to characterize the interaction ability of surfactant solutions used in enhanced oil recovery processes.  We are currently pursuing the characterization of additional dyes for this purpose.

We are currently studying interesting results obtained with halogenated solvents for these dyes.  In most non-halogenated solvents we observe a major peak with a shoulder on the high wavelength side of the peak.  In halogenated solvents, this is reversed, with the major peak toward the red and the shoulder on the blue side of the peak.  Such observations have been made for both methyl yellow and the merocyanine dyes.  Considerations currently include isomerization, the prominent transition being observed, concentration effects, and dye purity.  Computational studies may provide additional insights into which of these are more likely explanations than the others for our observations.

Future dye studies

We continue to pursue the characterization of the merocyanines with differing n-alkyl chain lengths attached to the nitrogen atom.  Between our studies and those in the literature, we aim to quantify the effects of increasing chain length on the dependence of the absorbance properties of Brooker’s merocyanine.

ACS-related activities and impact of the work on students:

Publications:  Two papers acknowledging the partial support of PRF were completed this year.  One has been published in Analytical Chemistry and the other has been accepted by the Journal of Chromatography as part of the annual Editor’s Choice volume in January, 2011.  This work relates to and was inspired by our interest in using LSERs to characterize micelle/solute interactions. 

ACS National Meeting, Boston:  I presented our spectroscopic work at the ACS fall meeting in Boston, 2010. 

Midwest ACS Meeting:  Two of my students, Andy Johnson and Ryan Johnson, presented our work at the regional ACS meeting in Iowa City in October, 2009.  Both students are planning to pursue graduate degrees in chemistry.  The opportunity to present their work at a regional meeting certainly helps prepare them for this goal.

Project SEED:  This year, just as last, two local high school students participated in the research.  One did so voluntarily because he did not meet the economic criteria.  The other was funded through the ACS Project Seed program. 

Summary: 

Overall, our work on the spectroscopic characterization of surfactant systems continues, with an increased attention to and need for computational studies.  We have also branched out into developing a new method that allows for easy visual comparison of literally thousands of separation systems.  Some of the work has already been presented at a national meeting and we have submitted abstracts for additional regional and national venues.  Two papers citing partial support from PRF were prepared this year, once of which has already been published and one which has been accepted and is scheduled to appear in early 2011.  We also have started initial efforts to collect the data in a form suitable for the submission of a manuscript based on our research.