Fluorene

Four new 2,1,3-benzooxadiazole-based donor-acceptor conjugated polymers, namely poly{9-(9-heptade-canyl)-9H-carbazole-alt-5,6-bis(octyloxy)-4,7-di(selenophen-2-yl)-benzo[c][1,2,5]oxadiazole)}(PSBSC), poly{9-(9-heptadecanyl)-9H-carbazole-alt-5,6-bis(octyloxy)-4,7-di(furan-2-yl)benzo[c][1,2,5]-oxadiazole)}(PFBFC), poly{9,9-dioctyl-9H-fluorene-alt-5,6-bis(octyloxy)-4,7-di(selenophen-2-yl)benzo[c][1,2,5]oxadiazole)} (PSBSFL), and poly{9,9-dioctyl-9H-fluorene-alt-5,6-bis(octy-loxy)-4,7-di(furan-2-yl)benzo[c][1,2,5]oxadiazole)}(PFBFFL), were synthesized via Stille polycondensation reaction. All polymers were found to be soluble in common organic solvents such as chloroform, tetrahydrofuran, and chlorobenzene. Their structures were verified by 1 H-NMR and the molecular weights were determined by gel permeation chromatography (GPC). The polymer films exhibited broad absorption bands. Among all polymers, photovoltaic cells based on the device structure of ITO/PEDOT:PSS/PSBSC:PC 71 BM(1:3, w/w)/LiF/Al revealed an open-circuit voltage of 0.62 V, a short circuit current of 7.63 mA cm 22 and a power conversion efficiency of 1.89%. This work demonstrates a good example for tuning absorption range, energy level, and photovoltaic properties of the polymers with different spacers and donor units can offer a simple and effective method to improve the efficiency of PSCs.

In this study, two donor-acceptor (D-A) type conjugated polymers namely PQSeCz and 15 PQSeFl were designed and synthesized. Selenophene was incorporated as a π-bridge, quinoxaline 16 as an acceptor unit while carbazole and fluorene were used as the donor units. Polymers were 17 synthesized via palladium catalyzed Suzuki polymerization reaction. All molecules were 18 characterized by 1 H and 13 C NMR Spectroscopy. The weight and number average molecular weights 19 of the two polymers were determined by gel permeation chromatography (GPC). Electrochemical 20 and spectroelectrochemical characterizations of the polymers were performed to investigate their 21 optoelectronic properties. Oxidation potentials were 1.15 V/ 0.82 V and 1.11 V/ 0.82 V for PQSeCz 22 and PQSeFl respectively, while reduction potentials were-1.26 V /-1.14 V and-1.48 V/-1.23 V, 23 respectively. In the visible region, maximum absorption wavelengths for the two polymers were 551 24 nm and 560 nm, respectively. Optical band gaps (Eg op) were found from the lowest energy π-π * 25 transition onsets as 1.71 eV and 1.58 eV, respectively. Both polymers showed good solubility in 26 common solvents. 27

Three novel donor-acceptor-donor type random copolymers based on benzothiadiazole (BTh) and benzoselenadiazole (BSe) were synthesized via Pd (0) catalyzed Suzuki polycondensation reaction. The two acceptor units were coupled with electron rich moieties which are carbazole (CZ), fluorene (FL) and silafluorene (SiFL). Monomers were characterized using 1
H and 13C-NMR spectroscopy. The number and weight average molecular weights of the polymers were calculated using gel permeation chromatography (GPC). All three polymers were electrochemically and spectroelectrochemically characterized. PBThBSeCZ, PBThBSeFL and PBThBSeSiFL showed only p-dopable character and their doping/dedoping potentials were determined as 1.4 V/1.2 V, 1.53 V/1.27 V and 1.8 V/1.3 V, respectively. Corresponding HOMO energy levels were calculated as -5.85 eV, -6.05 eV and -6.15 eV whereas LUMO energy levels were found to be -3.67 eV, -3.84 eV and -3.77 eV, respectively. PBThBSeCZ had lower HOMO level and band gap than PBThBSeFL and PBThBSeSiFL due to its increased electron donating capability of nitrogen atom in
carbazole unit.