Well-defined poly(3-hexylthiophene)-b-poly(quinoxaline-2

3-diyl)(P3HT-b-PQD) conjugated block copolymer was readily synthesized in one pot via mechanistically distinct

sequential living block copolymerization with Ni(dppp)Cl2 as a single catalyst at room temperature.The P3HT-b-PQD block copolymer gives yellow color in THF and exhibits strong light emission under UV irradiation at 365 nm.It was found that the synthesized P3HT-b-PQD copolymer can visually detect Co2+ in THF by changing its color from yellow to light green.The detection is of high selectivity as the addition of other metal ions did not induce any change on the solution color

including Pb2+

Na+

Al3+

K+

Mn2+

Fe2+

Fe3+

Zn2+

Ni2+

Ag+

Cu+

Cu2+

Eu3+

Cd2+

Mg2+

Ca2+

Cs+

Ba2+

Hg2+ and Pd2+.Moreover

the P3HT-b-PQD exhibits highly selective fluorescent senses of Co2+ over most of competing ions by changing its orange light emission to deep green in diluted THF solution.The detection limit of Co2+ by this P3HT-b-PQD block copolymer can be down to 10-7 mol/L.Further investigation revealed that the interference of other competing transition metal ions on the visual detection of Co2+ is negligible.Such visual detection of Co2+ by P3HT-b-PQD block copolymer can be put into practical applications by using test strips and thin films

making it a practical

convenient and highly selective visual cobalt probe by naked-eye.Transmission electron microscopy(TEM) observation indicated the P3HT-b-PQD was self-assembled into core-shell supramolecular structures upon coordinated with Co2+ ions.