The Effect of Side-Chain Length on the Solid-State Structure and Optoelectronic Properties of Fluorene-<i>alt</i>-Benzothiadiazole Based Conjugated Polymers—A DFT Study
Bibliographic record
Abstract
Using the dispersion corrected density functional theory (DFT-D/B97D) approach, we have performed bulk solid-state calculations to investigate the influence of side-chain length on the molecular packing and optoelectronic properties of poly (9,9-di-n-alkylfluorene-alt-benzothiadiazole) or FnBT's where n is the number of CH(2) units in the alkyl side-chains. Our results indicate that the FnBT's with longer side-chains in their most stable configurations, due to the significant intermolecular interactions between the side-chains, form lamellar crystal structures. On the other hand, for the FnBT's with shorter side-chains, two nearly degenerate stable crystal structures with nearly hexagonal symmetries have been found. These different packing structures can be attributed to the microphase separations between the flexible side-chains and the rigid backbones whose existence has been discussed in previous investigations for other hairy rod polymers. As a result of the efficient interchain interactions for the lamellar structures, the dihedral angle between the F and BT units is reduced by about 30°, providing a more planar configuration for the backbone. In turn, a more planar backbone leads to a decrease, about 0.2 and 0.3 eV, of the band gaps of the lamellar structures relative to the gap values for the gas and the nearly hexagonal phases, respectively. Time-dependent DFT (TD-DFT) was used to study the excited states of the monomers of FnBT's with various lengths of side-chains. TD-DFT study suggests that the absorption spectrum of the polymers with longer side-chains is red-shifted relative to the polymers with shorter side-chains and the gas phase.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".