## 3 Results
### UV-Vis Absorption and Fluorescence Properties  
UV-Vis absorption spectroscopy was employed to investigate the photophysical properties of **TPE-Se**, **TPE-Az**, **TPE-Su** and **TPE-Pi** (Figure 2). The electronic spectra of 1 \(\times\) 10\({}^{-5}\) M solutions of **TPE-Se**, **TPE-Az** and **TPE-Pi** showed absorption bands at 325 nm and 260 nm in THF, corresponding to \(\pi\)-\(\pi^{\text{t}}\) transitions. The UV-Vis spectrum of compound **TPE-Su** in the same solvent displayed the same absorption maxima at 325 nm but the shoulder peak at 260 nm was absent. It should also be noted that the shoulder peak for **TPE-Se** was batchromically shifted by around 10 nm to 270 nm relative to the other compounds. After establishing the absorption properties of **t **TPE-Se**, **TPE-Az**, **TPE-Su** and **TPE-Pi**, the emission properties of the four compounds were measured in THF solution. None of these four compounds showed photoluminescence in THF solution (Figure 3A-C and Figure S2). However, upon incremental addition of water to THF solutions of **TPE-Se**, **TPE-Az**, **TPE-Su** and **TPE-Pi**, the emission intensity for all four compounds was enhanced. In Figure 3A, the fluorescent emission properties of **TPE-Az** are shown. Compound **TPE-Az** was non-fluorescent in THF solution. With the addition of water to the THF solution of **TPE-Az** fluorescence emission intensity remained unchanged for \(f_{\text{w}}\) = 10-60% H\({}_{2}\)O/THF solutions. A slight change in intensity was observed at \(f_{\text{w}}\) = 70%. At \(f_{\text{w}}\) = 80%, a significant 90-fold fluorescence emission intensity enhancement was observed. The  
Figure 1: Luminescence properties: photographic images of (**A**) **TPE-Az** (**B**) **TPE-Su** (**C**) **TPE-Pi** in THF-water solvent mixtures with \(f_{\text{w}}\) values of 0%, 20%, 40%, 60%, 80% and 90% respectively, irradiated at 365 nm. emission peak was split into two peaks at 435 nm and 535 nm at \(f_{\rm w}\) = 90%, with an emission enhanced by 120 times compared to pure THF solution. The photoluminescence spectra of **TPE-Su** are shown in Figure 3B. Once again, a THF solution of **TPE-Su** did not show any emission. Upon incremental addition of water (10-60%) to THF solution, no emission spectral changes were observed. When the water fraction was increased to 70-80%, the emission spectra showed two split peaks at 395 nm and 535 nm, with a 120-fold increase in emission intensity compared to pure THF. Furthermore, in the THF/water (90%) mixture the peak at 395 showed a 30 nm red-shift, and the peak at 535 nm showed a 40 nm blue-shift. The new emission bands for **TPE-Su** at \(f_{\rm w}\) = 90% appeared at 425 nm and 495 nm. Similar studies were carried out for compound **TPE-Pi** in THF with increasing amounts of water (Figure 3C). Emission spectral changes were not observed for an increase in the water fraction between \(f_{\rm w}\) = 10-40%. A further increase in water fraction to \(f_{\rm w}\) = 50% resulted in a slight increase in emission intensity. With a water fraction of 70%, a 110-fold emission peak enhancement was observed at 475 nm compared to emission in pure THF. At \(f_{\rm w}\) = 80%, the emission peak was blue-shifted to 460 nm, and a further increase of water fraction to 90% led to a split emission peak, at 450 nm and 525 nm. Figure S2 displays the steady-state fluorescence spectra of the compound **TPE-Se** in THF and in THF/water solvent mixture. At first, the addition of water (10-50%) to THF solution resulted in no change in the emission spectra of **TPE-Se**. But when the water fraction was increased to 60% to 80%, an increase in emission intensity was observed. At \(f_{\rm w}\) = 90% the emission peak split into two peaks at 435 nm and 535 nm with rapid enhancement of intensity. Both peaks were red-shifted by 25 nm compared to \(f_{\rm w}\) = 80%. This is a clear demonstration of the AIE behaviour of **TPE-Se** aggregates via self-assembly.