Diketopyrrolopyrrole (DPP) containing oligomers and polymers draws significant attention due to its potential application in optoelectronic devices especially in bulk heterojunction solar cells. When compared to singlet excitons, triplet excitons are expected to result in efficient charge generation because of their longer lifetime, which allows their diffusion to the donor-acceptor interface. In this work we present the synthesis, photophysics of two distinct platinum containing DPP complexes named DPP-Pt(acac)  and DPP-Pt(C-C) consisting of cyclometallated Pt(acac) and platinum acetylide as end group respectively. The crystal structure of the precursor complex Pt(acac) shows slightly distorted square planar geometry around the platinum center. Both the complexes were photophysically characterized by absorption, emission, quantum yield of emission and emission lifetime studies. Covalent attachment of the heavy metal platinum to the DPP chromophore allows us to study the triplet state property by nanosecond transient absorption, due to its facile singlet to triplet intersystem crossing efficiency. Comparatively low fluorescence quantum yield and short fluorescence lifetime proved relatively fast intersystem crossing was taking place in DPP-Pt(acac), which was further supported by ultrafast transient absorption studies. Cyclic voltammetry study was performed for both these complexes to determine the frontier orbital (HOMO-LUMO) energy levels. Both the singlet and triplet state photophysics were verified by computational study. Although bulk heterojunction solar cell was prepared using DPP-Pt(acac), device thickness was limited by the solubility of the material. 

Ultrafast intersystem crossing in diketopyrrolopyrrole chromophore: Effect of cyclometallated platinum and platinum acetylide as end capper

248th National Meeting (2014)

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