Synthetic control over the energy transfer and charge transfer between carbon dots and covalent organic framework

Carbon dots (CDs) are environmentally benign, strongly photoluminescent, metal free nanoparticles. Interfacing them with tailor-made organic semiconductors possesing an ordered channel structure such as covalent organic frameworks (COFs) promises to yield multifunctional materials. In this study, microwave-derived CDs are successfully incorporated into the porous structure of COF in a one-pot synthesis in which the condensation reaction between benzo[1,2-b:4,5-b ']dithiophene-2,6-dicarboxaldehyde (BDT) and 1,1,2,2-tetra(p-aminophenyl)ethylene (ETTA) is conducted in the presence of CDs. A detailed structural and optoelectronic characterization of the COF/CDs composite reveals that upon tuning the CDs loadings encapsulated in COF the interaction between both components can be controlled allowing the switch between energy and charge transfer. At CDs loadings <= 20 wt%, strong binding of CDs to the COF enables charge transfer evinced from the quenched photoluminescence (PL) of both components and accelerated exciton decay kinetics of the COF. At CDs loadings >= 30 wt% Forster resonance energy transfer from CDs to COF prevails, leading to enhanced COF PL. Our study underlines the interaction mechanism in organic composites and provides the knowledge required for the design of novel functional materials with applications in photocatalysis, optoelectronics and sensing.