Synthesis and determination of fluorescence properties of new soluble diketopyrrolopyrrole type photosensitizers

Abstract

Four organic small molecules bearing phenyl diketopyrrolopyrrole (DPP) unit as the main acceptor group and indole as the main thermal group with soluble units, coded as DPP3(a-b) and DPP4(a-b), were synthesized and their optical/electrochemical properties were investigated. Intense visible absorption bands around 480 nm were assigned to the DPP main core, as well as bands around 600 nm were attributed to the formation of charge-transfer complex between the electron-rich indole units and electron-withdrawing DPP core in chloroform solution. All of the compounds were found to be fluorescent in solution and on thin films with emission wavelengths between 500 and 700 nm. The fluorescence decay kinetic measurements of these dyes were also studied. The synthesized compounds have electrochemical energy band gaps from 2.15 to 2.28 eV. Then, the potential usage of the final products in bulk heterojunction solar cells (BHJ-OSCs) were evaluated.