Singlet Fission in Colloidal Nanoparticles of Amphipathic Diketopyrrolopyrrole Derivatives: Probing the Role of the Charge Transfer State

Abstract

To evaluate the role of the charge transfer (CT) state in the singlet fission (SF) process, we prepared three 3,6-bis­(thiophen-2-yl)­diketopyrrolopyrrole (TDPP) derivatives with zero (Ph2TDPP), one (Ph2TDPP-COOH), and two (Ph2TDPP-(COOH)2) carboxylic groups, respectively. Their colloidal nanoparticles were also prepared by a simple precipitation method. The SF dynamics and mechanism in these colloid nanoparticles were investigated by using steady-state/transient absorption and fluorescence spectroscopy. Steady-state absorption spectra reveal that the strength of the CT resonance interactions between the adjacent DPP units is increased gradually from Ph2TDPP to Ph2TDPP-COOH and then to Ph2TDPP-(COOH)2. Fluorescence and transient absorption spectra demonstrate that SF is proceeded via a CT-assisted superexchange mechanism in these three nanoparticles. Furthermore, SF rate and yield are enhanced gradually with the increase of the number of the carboxylic group, which may be attributed to the enhancement of the CT coupling strength. The result of this work not only provides a better understanding of the SF mechanism especially for the role of the CT state but also gives some new insights for the design of efficient SF materials based on DPP derivatives.

Functionalized diketopyrrolopyrrole compounds for NIR-to-visible photon upconversion

“…Among the promising candidates are diketopyrrolopyrrole (DPP) based dyes, which were previously exploited in organic photovoltaics (OPVs), 36,37 organic light-emitting diodes (OLEDs) 38 and, in some cases, as singlet fission materials. [39][40][41] Recently, DPPs were also attempted in NIR-to-vis UC systems as annihilators of high stability. 1,42 The possibility to alter singlet energy of the DPP derivatives by modifying pendant aryl substituents was demonstrated, subsequently showing its impact on the UC yield in solutions; however, no systematic photophysical studies of this class of materials towards applicability for low-power upconversion were performed, thus leaving some space for advanced analysis and judgment.…”