Fig. 4

Photophysical properties of model compounds and polymers. a Reduction of model compound 4. b Reduction of P1a/2a. Inset: fluorescent photographs of THF solutions and powder of 4 and P1a/2a (left side) and 7 and P7 (right side). c Molecular orbitals of 4 and 7 in the ground state calculated by B3LYP/6-31G(d,p). d Schematic illustration of the modulation of fluorescence properties by the photoinduced electron transfer (PET) process. e Photoluminescence (PL) spectra of 7 in THF and THF/water mixtures with different water fractions (f_w). f Plot of the relative PL intensity (I/I₀) versus the composition of the aqueous mixtures of 7, P7, P1a/2d, and P1a/2e. α_AIE = I/I₀, where I₀ = intensity at f_w = 0%. Solution concentration: 10 μM. g Normalized PL spectra of the powder of 7, P7, P1a/2d, and P1a/2e and their associated fluorescent photographs. Excitation wavelength: 320 nm (for 7 and P7); 350 nm (for P1a/2d and P1a/2e). All fluorescent photographs were taken under UV irradiation at 365 nm.