EFFECT OF END GROUPS ON THE BAND GAP OF DONOR-ACCEPTOR BASED SMALL MOLECULES CONTAINING DIKETOPYRROLOPYRROLE

Abstract

(Acceptor-donor-acceptor type compounds 5,5'-(4,4'-(2,5-bis(2-octyldodecy1)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo [3,4-c]pyrrole-1,4-diyebis(4,1-phenylene))dithiophene-2-carbonitrile (DPPTCN), 4',4"-(2,5-bis(2-octyldodecy1)3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyedibipheny1-4-carbonitrile (DPPPhCN), 2,2'-(5,5'-(4,4T-(2,5-bis(2-octyldodecy1)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diy1)bis(4,1-phenylene)This(thiophene-5,2-diy1))- bis(methan-1-y1-1-ylidene)dimalononitrile (DPPT2CN), 2,21-(4',4"-(2,5-bis(2octyldodecy1)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo [3,4-c]pyrrole-1,4-diy1)bis(bipheny1-4',4-diy1))bis(methan-l-y1-1-ylidene)dimalononitrile (DPPPh2CN) were designed and synthesized. All the compounds have central diketopyrrolopyrrole common acceptor unit, the donor groups differ either thiophene or phenyl group and the terminal end groups are differ either nitrile or dicyanovinylene groups. In order to study the relationship between chemical structure and properties, their optical, thermal and electrochemical properties were investigated. Thermal properties indicate that all the compounds have high thermal stability. Among DPPT2CN with thiophene groups as donor and dicyanovinylene as acceptor has shown lowest LUMO energy level of -3.77 eV and low HOMO-LUMO band gap 1.86 eV.