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The solution photophysics of the isomeric aminobenzoic acids and N,Ndimethylaminobenzoic acids and their methyl esters were studied under a variety of conditions of solvent, pH, concentration and temperature. The most straightforward behaviour was obtained when the amino or N,N-dimethylamino substituent was in the meta- position relative to the carboxylic add or ester function. The amino compounds absorb with a peak between 300 and 325 nm depending on solvent, their fluorescence peaks lie between 350 and 410 rim. The corresponding N,N-dimethylamino compounds usually absorb and fluoresce some 20 - 30 rim to the red of these wavelengths. Both protonation and deprotonation of the ground state molecules takes place under weakly acidic conditions with pKi, values of approximately 3.0 and pK a values of approximately 5.0 being obtained. The observed variation in the fluorescence of the meta isomers with pH is largely caused by ground state equilibria. Förster cycle calculations suggest that the excited state pK a is little changed from the ground state whereas pKC is much smaller. This is in good agreement with the observed fluorescence data and the nature of the excited nglet state (usually some 10 -20 ns) than is seen for the other isomers. The fluorescence intensity of the meta- isomers was observed to rise with decreasing temperature, although this could possibly be attributed to absorbance changes. The photophysics of the corresponding ortho compounds is complicated by steric and hydrogen-bonding interactions especially in the compounds containing an N,N-dimethylamino group. The increased interaction between the two substituent groups leads to an increase in extinction coefficient and fluorescence quantum yield and a decrease in fluorescence lifetime for 2-aminobenzoic acid and its methyl ester compared to the meta derivatives. Spectral band positions, pK values and the effect of temperature on the fluorescence are similar in the two sets of compounds. The 2-N,Ndimethylamino compounds do not parallel the corresponding meta- derivatives due to steric hindrance and intra-molecular hydrogen bonding. These cause weak, blue shifted absorptions and low fluorescence quantum yields. There was no evidence found in this work for the presence of a zwitterionic species in the absorption properties of 2-N,N-dimethylaminobenzoic acid. The photophysical properties of 4-aminobenzoic acid and its methyl ester are in many ways very similar to those of the corresponding orthosubstituted compounds. However the same certainly cannot be said for 4-N,Ndimethylaminobenzoic add and its methyl ester. These two compounds exhibit anomalous fluorescence in the form of two fluorescence bands in some solvents. The appearance of this anomalous fluorescence is both concentration and solvent composition dependent. Various mechanisms to explain these observations were tested; excimer, exciplex, TICT state and ground state dimer formation. The latter was found to be in best accord with the properties of these molecules, but it was clear that in binary solvent mixtures such as hexane / acetonitrile and acetonitrile / water other mechanisms could also be involved.

Nitrogen use efficiency (NUE) in cereal crops is at 33% on a global scale. Winter Wheat (Triticum aestivum) is one of the major cereal crops being affected by low NUE. Winter wheat is grown across the United States and the world alike and nitrogen is one of the most applied plant nutrients to winter wheat. With great abundance and low world efficiency rates, the need for increasing NUE is paramount. This study looked at varying nitrogen rates, their placement mid-season, and their effects on grain yield. Actual application took place between Growing Degree Days (GDD) greater than zero (GDD > 0) of 90 and 110 to supply the plant with the precise amount of nitrogen needed before its largest vegetative growth stage. The study was conducted in 2020 at four locations across Oklahoma: Lahoma, Hennessey, Perkins, and Stillwater. All studies employed a randomized complete block design with Urea Ammonium Nitrate (UAN) (28-0-0) as the only nitrogen source used. Placement of the UAN was varied between surface applied and sub-surface applied, nitrogen rates varied between 0 kg/ha to 168 kg/ha. Results of this study were mainly inconclusive to the hypothesis that mid-season subsurface applied UAN would yield higher than surface applied UAN at similar N-rates. The supporting optical sensor reading data was also inconclusive. The most significant differences were higher yields when UAN was surface applied. High yields when UAN was surface applied was attributed to the high amount of precipitation that occurred shortly after the midseason application.