Torsion Angles between Donor and Acceptor Moieties as a Descriptor for Designing Nonlinear Optics and Thermally Activated Delayed Fluorescence Materials

The performances of nonlinear optics (NLO) and thermally activated delayed fluorescence (TADF) materials are strongly related to the torsion angles (theta) between donor (D) and acceptor (A) moieties in D-A architecture molecules. However, the underlying relationships connecting theta to the performances of NLO/TADF materials remain unclear. Herein, we present a comprehensive theoretical study on NLO/TADF materials composed of a series of D-A backbone molecules (TPAAP/TPAAQ series and AQ-DMAC/AQ-MeFAC series) to shed light on these relationships. It is found that changing theta via the intramolecular locking strategy can greatly influence values of the first hyperpolarizability (beta) and singlet-triplet energy gap (Delta E-ST), further leading to better/worse performances of NLO/TADF materials, respectively. Intriguingly, a more detailed analysis indicates that the variation trends between theta and beta/Delta E-ST are changeable in low theta regions, exhibiting volcano-like relationships. The large coefficients of determination (R-2, ranging from 0.76 to 0.93) suggest that this experimentally measurable parameter (theta) can be used as a promising descriptor to evaluate the performances of related materials. Following the revealed theta-beta/theta-Delta E-ST correlations, the optimal/worst torsion angles for different materials are identified. These findings highlight the importance of the intrinsic structure-performance relationships, thus providing novel design strategies for high-performance NLO/TADF materials.

Automated summary

This study investigates the relationship between the performance of nonlinear optics (NLO) and thermally activated delayed fluorescence (TADF) materials and the torsion angles (theta) between the donor (D) and acceptor (A) moieties in D-A backbone molecules. By changing the torsion angle, the values of the first hyperpolarizability (beta) and singlet-triplet energy gap (Delta E-ST) of the materials can be significantly influenced, leading to improved or worsened performances of NLO/TADF materials. The results suggest that the experimentally measurable parameter (theta) can serve as a promising descriptor to evaluate the performance of related materials, providing novel design strategies for high-performance NLO/TADF materials.