Charge Transfer Dye in Various Polymers with Different Polarity: Synthesis, Photophysical Properties, and Unusual Aggregation-Induced Fluorescence Changes

A new pyran-based CTD monomer, allyl 2-(2,6-bis((E)-4-(dimethylamino)styryl)-4H-pyran-4-ylidene)-2-cyanoacetate (2), was successfully synthesized by Knoevenagel reaction. Copolymerization of 2 with styrene (St), methyl methacrylate (MMA), and acrylonitrile (AN) afforded copolymers with different polarity, P(St-co-2), P(MMA-co-2), and P(AN-co-2), respectively. IR and UV-vis absorption spectra revealed that 2 is incorporated into the copolymers. The 2 in the copolymers exhibited absorption and fluorescence properties which are completely different from 2. All these copolymers showed significant blue shifts in emission relative to 2. Also, their lambda(max,abs) and lambda(max,em) increased with an increase in dielectric constant (epsilon) of the polymer matrix in order PAN (epsilon = 5.5) > PMMA (3.3) > PSt (2.5). The copolymers in DMF showed blue shifts in emission along with aggregation by addition of methanol while copolymers in 1,4-dioxane showed a red shift. The fluorescence intensity of P(St-co-2) and P(MMA-co-2) decreased by aggregation while that of P(AN-co-2) increased.