Single molecule of a π-conjugated polymer slowly twinkles in solution at room temperature

Abstract

A phenylacetylene monomer, 4-(decyloxycarbonyl)phenylacetylene (DecCPA), was synthesized and polymerized using the combined catalyst system, i.e. [Rh(norbornadiene)Cl]2 and triethylamine, to give a yellow solid π-conjugated polymer [poly(DecCPA)] of high molecular weight and cis-transoidal stereo-regular main chain. Poly(DecCPA) was measured using the total internal reflection fluorescence microscopy, which is a single molecule detection technique that is carried out in a tetrahydrofuran solution at room temperature with the light-twinkling of a single molecule being observed. This twinkling is a dynamic photon emission phenomenon of single poly(DecCPA) molecule that we mention specifically as a resultant from the time scale — changing very slowly in the time scale of milliseconds and seconds — with the changed fluorescent intensity being associated with the changing single polymer molecule conformation caused by the micro-Brownian motion. Although molecular dynamics was of the picosecond time scale, generally, this poly(DecCPA) molecule had the mode of the molecular motion of π-conjugated main chain. This was very slow in the second time scale as was shown.