Effect of Hexyl Substituent Groups on Photophysical and Electrochemical Properties of the Poly[(9,9-Dioctyfluorene)-2,7-Diyl-alt-(4,7-bis (3-Hexylthien-5-Yl)-2,1,3-Benzothiadiazole)-2 ',2 ''-diyl] (vol 54, pg 1975, 2016)