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 γ_max,abs and γ_maxem increased with an increase in dielectric constant (e) of the polymer matrix in order PAN (e = 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.