Conjugation- and Aggregation-Directed Design of Covalent Organic Frameworks as White-Light-Emitting Diodes

Abstract

2D covalent organic frameworks (COFs) have emerged as a promising class of organic luminescent materials due to their structural diversity, which allows the systematic tuning of organic building blocks to optimize emitting properties. However, a significant knowledge gap exists between the design strategy and the fundamental understanding of the key structural parameters that determine their photophysical properties. In this work, we report two highly emissive sp 2 -C-COFs and the direct correlation of the structure (conjugation and aggregation) with their light absorption/emission, charge transfer (CT), and exciton dynamics, the key properties that determine their function as luminescent materials. We show that white light can be obtained by simply coating COFs on an LED strip or mixing the two COFs. Using the combination of time-resolved absorption and emission spectroscopy as well as computational prediction, we show that the planarity, conjugation, orientation of the dipole moment, and interlayer aggregation not only determine the light-harvesting ability of COFs but also control the exciton relaxation pathway and photoluminescent quantum yield.

The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push–pull chromophores

“…where the bra/ket notation refers to integration with respect to r h and r e . 28 The exciton size, defined in this way, is a transferable measure that provides insight into charge transfer between isolated molecules, 28 covalently bonded donor-acceptor systems, 63 as well as large conjugated π-systems. 29 Purely local excitations generally have a d exc of 4 Å or less, where anything above this value indicates at least partial CT character.…”

Visible Light‐Regulated Heterogeneous Catalytic PET‐RAFT by High Crystallinity Covalent Organic Framework

“…[ 50,51 ] The high regular overlaps of π arrays between each layer provides pre‐organized pathway for the transportation of charge‐carries. [ 52–55 ] By virtue of the availability of ligands with functional chemical properties and diversity of charming topologies structure, COFs have been investigated as photocatalyst for converting solar energy into chemical energy via photocatalytic CO 2 reduction, [ 56–58 ] water splitting, etc. [ 59,60 ] Our recent work has reported pyrene‐based TFPPy‐Td‐COFs as highly effective photocatralyst for controlling polymerization of a variety of methacrylate monomers by photo‐induced ATRP, [ 61 ] confirming the feasibility of COFs as heterogeneous catalyst for mediating photocontrolled RDRP.…”

Electroactive covalent organic frameworks: a new choice for organic electronics

“…The most common method to incorporate COFs into LEDs is to use the COF as a phosphor. This is done by coating an inorganic blue LED with a yellow-light-emitting COF material (Figure 4C), and several examples of this approach exists [73][74][75][76]. Using the COF as the active layer in an OLED requires both conductivity and emissivity.…”