4 research outputs found
Spectrally Switchable Photodetection with Near-Infrared-Absorbing Covalent Organic Frameworks
Most covalent organic frameworks
(COFs) to date are made from relatively
small aromatic subunits, which can only absorb the high-energy part
of the visible spectrum. We have developed near-infrared-absorbing
low bandgap COFs by incorporating donor–acceptor-type isoindigo-
and thienoÂisoindigo-based building blocks. The new materials
are intensely colored solids with a high degree of long-range order
and a pseudo-quadratic pore geometry. Growing the COF as a vertically
oriented thin film allows for the construction of an ordered interdigitated
heterojunction through infiltration with a complementary semiconductor.
Applying a thienoÂisoindigo-COF:fullerene heterojunction as the
photoactive component, we realized the first COF-based UV- to NIR-responsive
photodetector. We found that the spectral response of the device is
reversibly switchable between blue- and red-sensitive, and green-
and NIR-responsive. To the best of our knowledge, this is the first
time that such nearly complete inversion of spectral sensitivity of
a photodetector has been achieved. This effect could lead to potential
applications in information technology or spectral imaging
Oligothiophene-Bridged Conjugated Covalent Organic Frameworks
Two-dimensional covalent organic
frameworks (2D-COFs) are crystalline,
porous materials comprising aligned columns of π-stacked building
blocks. With a view toward the application of these materials in organic
electronics and optoelectronics, the construction of oligothiophene-based
COFs would be highly desirable. The realization of such materials,
however, has remained a challenge, in particular with respect to laterally
conjugated imine-linked COFs. We have developed a new building block
design employing an asymmetric modification on an otherwise symmetric
backbone that allows us to construct a series of highly crystalline
quaterthiophene-derived COFs with tunable electronic properties. Studying
the optical response of these materials, we have observed for the
first time the formation of a charge transfer state between the COF
subunits across the imine bond. We believe that our new building block
design provides a general strategy for the construction of well-ordered
COFs from various extended building blocks, thus greatly expanding
the range of applicable molecules
Synchronized Offset Stacking: A Concept for Growing Large-Domain and Highly Crystalline 2D Covalent Organic Frameworks
Covalent
organic frameworks (COFs), formed by reversible condensation
of rigid organic building blocks, are crystalline and porous materials
of great potential for catalysis and organic electronics. Particularly
with a view of organic electronics, achieving a maximum degree of
crystallinity and large domain sizes while allowing for a tightly
Ï€-stacked topology would be highly desirable. We present a design
concept that uses the 3D geometry of the building blocks to generate
a lattice of uniquely defined docking sites for the attachment of
consecutive layers, thus allowing us to achieve a greatly improved
degree of order within a given average number of attachment and detachment
cycles during COF growth. Synchronization of the molecular geometry
across several hundred nanometers promotes the growth of highly crystalline
frameworks with unprecedented domain sizes. Spectroscopic data indicate
considerable delocalization of excitations along the π-stacked
columns and the feasibility of donor–acceptor excitations across
the imine bonds. The frameworks developed in this study can serve
as a blueprint for the design of a broad range of tailor-made 2D COFs
with extended π-conjugated building blocks for applications
in photocatalysis and optoelectronics
Synchronized Offset Stacking: A Concept for Growing Large-Domain and Highly Crystalline 2D Covalent Organic Frameworks
Covalent
organic frameworks (COFs), formed by reversible condensation
of rigid organic building blocks, are crystalline and porous materials
of great potential for catalysis and organic electronics. Particularly
with a view of organic electronics, achieving a maximum degree of
crystallinity and large domain sizes while allowing for a tightly
Ï€-stacked topology would be highly desirable. We present a design
concept that uses the 3D geometry of the building blocks to generate
a lattice of uniquely defined docking sites for the attachment of
consecutive layers, thus allowing us to achieve a greatly improved
degree of order within a given average number of attachment and detachment
cycles during COF growth. Synchronization of the molecular geometry
across several hundred nanometers promotes the growth of highly crystalline
frameworks with unprecedented domain sizes. Spectroscopic data indicate
considerable delocalization of excitations along the π-stacked
columns and the feasibility of donor–acceptor excitations across
the imine bonds. The frameworks developed in this study can serve
as a blueprint for the design of a broad range of tailor-made 2D COFs
with extended π-conjugated building blocks for applications
in photocatalysis and optoelectronics