Macromolecular Effect Stabilized Color-Tunable and Room Temperature Charge-Transfer Complexes Based on Donor–Acceptor Assemblies

Abstract

We report one of the first examples of room temperature stable solid-state charge transfer (CT) complexes based on a segmented π-conjugated polymer and rylene diimide donor–acceptor system having tunable optical transitions from the visible to NIR region in the solar spectrum. Semicrystalline and amorphous segmented oligo-phenylenevinylene (OPV) chromophore containing polymers were tailor-made with flexible polymethylene chains in the backbone. The electron rich segmented OPV polymers were complexed with two electron-deficient diimides based on naphthalene (NDI) and phenylene (PDI) core. The binary complexes of segmented OPV polymers and rylene diimides produced unique classes of CT complexes based on OPV-NDI and OPV-PDI chromophore diads. Electron microscope, polarizing microscope, and X-ray diffraction analyses provided direct evidence for the two-dimensional lamellar packing of D–A self-assembly in the solid state. Detailed absorption and emission photophysical studies revealed that the donor OPV polymers and acceptor chromophores exhibited a 1:1 complex with respect to the long-range order of D–A–D–A–D–A π-stacked supramolecular assemblies. The role of the macromolecular effect on the CT complexation was further investigated using structurally identical OPV monomers. The monomer OPV-NDI complexes (or PDI complexes) were found to exhibit CT complex in the solution; however, they underwent uncontrollable phase separation into their individual D and A crystalline domains and lost their CT self-assembly in the solid state. Interestingly, the macromolecular effect driven supramolecular self-organization of long chain segmented OPV polymers produced stable CT complexes both in solution and solid state under ambient conditions. Segmented OPV polymer + PDI and segmented OPV polymer + NDI complexes were produced as red and green colored CT complexes, respectively. This enabled the accomplishment of room temperature stable CT complexes in π-conjugated polymers having absorption ranging from 350 to 1100 nm. These donor–acceptor CT self-assemblies are processable into thin films under solvent free melt crystallization process; thus, the present segmented polymer design strategy opens up a platform for donor–acceptor CT complexes.

Electron Transfer in Conjugated Polymer Electrolyte Complexes: Impact of Donor–Acceptor Interactions on Microstructure, Charge Separation, and Charge Recombination

“…Notably, no significant polaron-pair feature is observed with MV 2+ :RR-E or ENDI:RR-B; this provides further support that the polymer chains interact co-facially with the acceptors, preventing direct polymer–polymer interactions. However, the observation of H-like aggregate excitonic coupling implies interstrand dipolar coupling, which points to a stacked structure of alternating or interleaving donor and acceptor layers such that complexes have some greater degree of supramolecular assembly . Given that polaron pairs are commonly observed for stacked polymer morphologies, our data suggests that ENDI-PTAK complexes may be best visualized as small assemblies with interdigitating layers of co-facially stacked donors and acceptorsresulting in H-like excitonic coupling between polymer strands within stacks, but with co-facial donor–acceptor interactions inhibiting direct interstrand orbital interactions and, therefore, polaron-pair formation.…”

“…However, the observation of H-like aggregate excitonic coupling implies interstrand dipolar coupling, which points to a stacked structure of alternating or interleaving donor and acceptor layers such that complexes have some greater degree of supramolecular assembly. 74 Given that polaron pairs are commonly observed for stacked polymer morphologies, our data suggests that ENDI-PTAK complexes may be best visualized as small assemblies with interdigitating layers of co-facially stacked donors and acceptors�resulting in H-like excitonic coupling between polymer strands within stacks, but with co-facial donor−acceptor interactions inhibiting direct interstrand orbital interactions and, therefore, polaron-pair formation. This is consistent with the previously noted competition between polaron and polaron-pair formation in ENDI:RR-B complexes with variation in acceptor ratio: charge separation between RR butanoate and ENDI:polar-pairs are generated more efficiently in low vs high ratio ENDI:PTAK CPECs, which is attributable to a decreased acceptor density and differences in PTAK microstructure.…”

Sequence-complementarity dependent co-assembly of phosphodiester-linked aromatic donor-acceptor trimers

“…S10). Thermochromism in aromatic CT complexes [30][31][32] has been observed to occur via structural reorganisation [33] and phase separation. [34] Since phase separation would result in two CT-active compounds, it must be a degree of conformational reorganisation upon interaction of the two compounds which is occurring.…”

Charge-Transfer-Induced Self-Assembly of Doped Conjugated Block Copolymer Nanofibers

“…Complete quenching of P3HT photoluminescence at 570 nm with the addition of F4TCNQ also supports efficient CT interactions (Figure 1c). 35,36 The ground state CT was also confirmed by X-band electron paramagnetic resonance (EPR) spectroscopy (Figure 1d). The P3HT-b-PEO/F4TCNQ mixture showed an EPR signal with a g-factor of 2.001 from P3HT radical cations, 28,18 which was absent in the P3HT-b-PEO spectrum without F4TCNQ.…”