A novel fluorene-phenylene (FP) based cross-conjugated copolymer with donor-acceptor (D-A) architecture was synthesized by palladium-catalyzed Suzuki coupling reaction.In sample P1

the dibutylamino was introduced into the side chain

used as electron donor and ion receptor; the 2

1

3-benzothiadiazole was incorporated into the backbone and served as electron acceptor.For comparison

sample P2 without 2

1

3-benzothiadiazole moieties was also prepared.The chemical structure of P1 and P2 was confirmed by 1H-NMR

IR

elemental analysis and GPC.Cyclic voltammetry (CV) was used to assess the electrochemical behavior of the polymers.The HOMO levels of the P1 and P2 estimated from CV were -4.87 eV and -4.86 eV

respectively; the LUMO levels of P1 and P2 were -2.47 eV and -2.09 eV

respectively

that were consistent with the energy levels calculated by B3LYP/6.31G method.The results indicated that the manipulation of the energy levels of the HOMO and LUMO can also be achieved by the incorporation of donor-acceptor (D-A) moieties within cross-conjugated polymer systems.The presence of strong intramolecular charge transfer (ICT) in P1 was supported by the frontier orbital distribution calculated by AM1 method.Due to the ICT interactions

both the fluorescence emission of P1 and P2 exhibited strong solvatochromic effect，the fluorescence intensity of P1 decreased greatly with the increase the solvent’s polarity.The optical sensing properties of P1 and P2 in dichloromethane were investigated upon addition with Cu2+

Zn2+ and H+

respectively.P1 and P2 exhibited completely dissimilar optical response to cation

which can be ascribed to much stronger ICT effect in P1 Interestingly

by adding Cu2+

Zn2+ or H+ into P1 solution

the fluorescence intensity was amplified

which was descried as a “turn-on" effect.The dramatic result was attributed to a strong modulation of ICT interactions by complexation with cation.However

upon coordination with a small amount of Cu2+

the emission of P2 (470 nm) was quenched and redshifted to 512 nm; when the concentration of Cu2+was increased

the emission of P2 was blueshifted to 435 nm.These preliminary results showed that the FP based cross-conjugated polymers with D-A structure can be served as potential sensory materials with “turnon" property.