## 3 Results and Discussion
### Optical Properties of Benztriimidazole Materials  
The optical properties of all six benzotriimidazole compounds were measured by UV-VIS and fluorescence spectroscopy in dichloroethane. Tris Ph will be considered the model compound which will be compared to molecules with different electron donor substituents (Tris OMe and Tris butyl) and electron withdrawing substituents (Tris CN, Tris CN\({}_{2}\)F, Tris CN\({}_{3}\)F) on the phenyl pendants. Absorption and emission spectra for each compound are shown in Figure 3.  
Figure 3: Optical spectra of benzotriimidazole-based materials. Solid line: absorption. Dotted line: photoluminescence. All of the benzotriimidazole compounds have \(\pi\)-\(\pi^{\bullet}\) absorption bands in the range of 250-400 nm. These values strongly depend on the electron withdrawing character of the substituents on the phenyl pendants. When no substituent is used, as with Tris Ph, maximum absorption occurs at 300 nm. Very little change is observed in the absorption spectrum when electron donating methoxy substituents are introduced with Tris OMe. Slightly electron-donating tert-butyl substituents were used to improve solubility of Tris butyl, and the absorption spectrum is similarly indistinguishable from Tris Ph. When electron withdrawing substituents are introduced into the system, there is a clear effect on the optical properties. The absorption spectra are shifted 50-60 nm to longer wavelengths despite the electron withdrawing phenyl pendants not being directly conjugated to the \(\pi\)-system of the benzotriimidazole core. The simplest of these, Tris CN, utilizes cyano-phenyl pendants and has peak absorption at 354 nm. A second electron withdrawing substituent was introduced with Tris CN\({}_{3}\)F, a fluorine atom ortho to the cyano group of each phenyl pendant. This resulted in further red-shifted the peak absorption at 362 nm. When the fluorine atom is meta to the cyano group on the phenyl pendant, as with Tris CN\({}_{2}\)F, the observed redshift is not quite as drastic, with peak absorption at 360 nm. Upon excitation at absorption \(\lambda_{max}\), the benzotriimidazoles that do not possess electron-withdrawing groups exhibit violet-blue photoluminescence (PL). Tris Ph, Tris OMe, and Tris butyl have very similar PL spectra with maxima at 408, 406, and 405 nm, respectively, and all three emit over the range of 350-550 nm. The full-width at half-maximum (FWHM) for the PL spectra of all three molecules is approximately 72 nm. Conversely, the benzotriimidazoles with electron-withdrawing groups display very strong blue PL slightly red-shifted to the range of 400-600 nm. The PL spectrum of Tris CN has \(\lambda_{max}\) of 445 nm and FWHM of 80 nm. Tris CN\({}_{2}\)F and Tris CN\({}_{3}\)F have almost identical PL spectra and are slightly red-shifted even further from Tris CN with \(\lambda_{max}\) at 453 nm and similar, slightly broadened FWHM of 82 nm. The electron withdrawing groups shift the emission to a longer wavelength, towards a more \"true blue\" color. The PL quantum efficiency of each benzotriimidazole depends strongly on the presence of electron-withdrawing groups. PL quantum efficiencies of benzotriimidazoles without electron-withdrawing groups were less than desirable (40-43%) while molecules with electron-withdrawing groups displayed much stronger PL with efficiencies in the range of 73-75%. The electron withdrawing groups on the phenyl pendants enhance emission efficiency by pulling electron density away from the already electron-deficient benzotriimidazole core, making a reasonable fluorophore into a very strong one. There is negligible disparity in PL quantum efficiency between molecules with only CN on the phenyl pendants and molecules with CN and F. The enhancement in PL quantum efficiency is likely maximized by a single electron withdrawing group (EWG) in the para position on each pendant. The para position on the pendants appears to be most effective at drawing electron density from the core of the benzotriimidazole.