As we all know that tetraphenyl ethylene (TPE) is a typical AIE-active chromophore [
48]. Therefore, the aggregation behavior of TPE-TPE and TPE-TPE-CN in solid state and
N,N-dimethylformamide (DMF)/water mixture with different water fractions (
fw) is studied, respectively. As shown in
Fig. 1a, TPE-TPE powder exhibits strong blue light emission with a maximum emission wavelength (λ
em) of 452 nm under ultraviolet (UV) light at 365 nm, while TPE-TPE-CN strong green light emission with a λ
em of 516 nm in its solid state under the UV light. Furthermore, the fluorescent quantum yield (
ФF) values of TPE-TPE and TPE-TPE-CN in solid are 16.96% and 63.19%, respectively. In solution, the photoluminescence (PL) intensity of TPE-TPE at 471 nm is low with a very weak blue-light emission and a
ФF value of 16.26% in pure DMF (Table S1 in Supporting information). With the increase of water (
fw < 40%), its PL intensity at 471 nm shows little change. But when more water was added (
fw > 40%), the PL intensity was drastically increased and even up to 263.07-fold with a bright blue light emission and a
ФF value of 66.11% in 90% water/DMF mixture (
Figs. 1b and
d). Moreover, according to the UV–visible (UV–vis) absorbance spectrum of TPE-TPE, a level-off tail effect can also be observed between 400 nm and 500 nm when
fw > 40% due to the gradual formation of organic nanoparticles (Fig. S1a in Supporting information). While its PL intensity at λ
em exhibits little decrease when more water is added (60% <
fw <90%) due to the strong interaction between the polar solution and the nanoparticles. Scanning electron microscope (SEM) and dynamic light scattering (DLS) analysis show that the average diameter of nanoparticles is 183.70 nm with a narrow distribution of 0.184 (Figs. S2a and b in Supporting information). Similarly, the PL intensity of TPE-TPE-CN at 514 nm is also weak with a
ФF value of 9.50% in pure DMF, but with the increase of water fraction in DMF/water mixture (
fw < 40%), its PL intensity is gradually enhanced to 1.51-fold its original state. However, when more water was added (
fw > 40%), the PL intensity at 514 nm drastically increased to 40.25-fold its original state and remained stable around 41-fold with a
ФF value of 61.30% in 90% water/DMF solution, and a level-off tail can also be obtained in its UV–vis absorbance spectrum, which can also be put down to the gradual formation of nanoparticles (
Figs. 1c,
d and Fig. S1b in Supporting information). The average diameter of nanoparticles is 207.20 nm and the polydispersity index (PDI) is 0.235, suggesting the formation of nanoparticles in 90% water/DMF solution (Figs. S2c and d in Supporting information). Moreover, the morphology and average diameter of these two types of organic nanoparticles show little change after 48 h (191.8 nm for TPE-TPE and 209.5 nm for TPE-TPE-CN, respectively), demonstrating good long-term stability of sulfates-based nanoparticles (Fig. S3 in Supporting information). All of the above demonstrates the typical AIE characteristic of these two TPE-based derivatives both in their solid and aggregated state.