Theoretical and experimental investigation of solvatochromic and photochromic materials

This thesis includes a study of solvatochromic molecules in the liquid and gas phases, and a study of photochromic molecules in the solid phase. The solvatochromic molecules studied are Nile Red, Betaine 30 and its penta tert-butyl substituted analog Betaine 45, 4-DMABN and its derivatives, as well as N-phenyl-benzohydroxamic acid and its derivatives. The photochromic molecule of study was the spiropyran molecule commonly known as 6-NO 2-BIPS, which was investigated in polymer media.;A TD-DFT study using a polarizable continuum solvent model was perfomed on Betaine 30. Several correlation plots of the experimental vs. Theoretical ENT (our work) were made and evaluated. It was found that TD-DFT excitation energies were overestimated in non-polar solvents and underestimated in the more polar solvents. The inclusion of explicit solvation was found to improve the plot of Experimental vs. Theoretical ENT such that a conversion equation ENTExperimental = (0.832) ENTTheoretical + 0.029 with and r2=.954 be made.;A TD-DFT study on the first three excitation energies of 4-aminobenzontrile, 4-(N,N)-dimethylaminobenzontrile (DMABN), its ethyne analog (DMABE) and a fluorinated ethyne analog (DMABFE) was made to gain insight into why DMABN exhibits dual fluorescence while the others do not. The excited state energies were monitored indirectly using TD-DFT in gas phase and in cyclohexane and acetonitrile well as simulated in the solvents cyclohexane and acetonitrile. A lowering of the second lowest lying excited state was found to surpass the lowest lying excited state, which provides evidence that fluorescence could occur from two different states. A reversal of states was observed for one of the four molecules, as observed experimentally, but this rationale could not explain why Nile Red exhibits dual fluorescence.;A TD-DFT study of four para-N-substituted N -phenylbenzohydroxamic acids was carried out to determine the effects of substitution and solvation on conformation (cis/trans), absorption and pKA. The study successfully characterized the effects of substitution, conformation, deprotonation and solvation on the excitation energies using TD-DFT. PKA values were also reported, where the inclusion of explicit solvation was found to moderately improve them relative to experimental data.;Calculation of the change in electronic dipole moment from the ground to the first excited state of Nile Red was accomplished by experimental and theoretical methods. Nile Red possessed a structured absorption band with two maxima, which caused a dilemma as to which absorption maximum to pair with the emission maximum for the purpose of calculating Stokes Shift. For this reason, the average Deltamu was found to be 2.38 D +/- 0.76 D, when using an absorption maxima that red-shifts like the emission maxima, and 2.81 D +/- 0.96 D when using a maxima that is stationary. A Configuration Interaction Singles (CIS) and Time-Dependent Density Functional Theory (TD-DFT) study using a polarized continuum solvent model to study the effects of solvation, geometry, excitations and their relationship with each other was also carried out. The calculated Deltamu value from HF and CIS techniques was found to be 2.24 D in acetonitrile, which is comparable to that found from our experimental investigation.;A kinetic study on the ring-closure of 6-NO2-BIPS to its colourless spiropyran form was studied in polystyrene, poly tert-butyl styrene, polymethyl methacrylate, poly n-butyl methacrylate, polyvinyl acetate and polycarbonate. Physical properties of the polymers such as glass transition temperature (T g), free volume and polarity all affected the rate of decoloration. The Tg and free volume was also found to affect absorption maxima, causing a blue-shift to the lambdamax of 6-NO2-BIPs in polymers with lower Tg values and as polarity increased. The addition of the plasticizer dibutyl phthalate (DBP) to the polymer resulted in an increased decoloration rate by decreasing Tg. Several other plasticizers were investigated in polycarbonate exclusively and all were found to increase the rate of decoloration. However, a link between the structure of the plasticizer and its effect on the rate of discoloration could not be established.