Insights into the Photobehavior of Fluorescent Oxazinone, Quinazoline, and Difluoroboron Derivatives: Molecular Design Based on the Structure–Property Relationships

Abstract

Systematic comparisons among the oxazinone, quinazoline, and difluoroboron series on optical absorption and fluorescence emission properties have been made. Weaker electron donor–acceptor (D–A) pairs in both the oxazinone and quinazoline series bring about the slight red shifts of absorption spectra, whereas they significantly promote the fluorescence intensities of the oxazinone series but bathochromically shift the maximum emission wavelengths of the quinazoline series. Intrinsically, the charge-transfer (CT) modes govern the electron excitation/de-excitation processes in both the oxazinone and quinazoline series, but with respective different CT features, i.e., the interfragment CT mode for the oxazinone series versus the intrafragment CT mode for the quinazoline series. In the difluoroboron series, Oxa-Cl-OCH3-BF2 undergoes a change of transition mode from the local excitation to the CT de-excitation, whereas a large variation of CT compositions can be observed in Qui-Cl-OCH3-BF2. Experimentally, Oxa-Cl-OCH3-BF2 exhibits higher fluorescence quantum yield, favorable thermo- and photostability, stronger fluorescence intensity, and appropriately large Stokes shift, whereas theoretically, Qui-Cl-OCH3-BF2 benefiting from both the difluoroboron and quinazoline moieties is also promising to be a good fluorescent dye. The motif of combining oxazinone/quinazoline and difluoroboron moieties is believed to improve the prototypical architectures of oxazinone and quinazoline dyes.

Meta Junction Promoting Efficient Thermally Activated Delayed Fluorescence in Donor‐Acceptor Conjugated Polymers

“…Since they contain the same D and A units in the backbone, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels are taken to almost match with each other (Supporting Information, Table S1). Subsequently, considering that Δ E ST is sensitive to the exchange interactions on the overlap between hole and electron wave functions, the vertical excitation calculation is conducted by TD‐DFT at the same level using the optimized molecular structures, followed by the hole and electron analysis on S 1 and T 1 states. As one can see in Figure , both the hole and electron of S 1 are distributed along the polymeric chain, and a large electron–hole overlap (S m index=0.1609) is determined for poly(TPAp‐DCBp).…”

Meta Junction Promoting Efficient Thermally Activated Delayed Fluorescence in Donor‐Acceptor Conjugated Polymers

“…Since they contain the same Da nd Aunits in the backbone, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels are taken to almost match with each other (Supporting Information, Table S1). Subsequently,c onsidering that DE ST is sensitive to the exchange interactions on the overlap between hole and electron wave functions, [20] the vertical excitation calculation is conducted by TD-DFT at the same level using the optimized molecular structures,followed by the hole and electron analysis [34,35] on S 1 and T 1 states.A so ne can see in Figure 2, both the hole and electron of S 1 are distributed along the polymeric chain, and al arge electron-hole overlap (S m index = 0.1609) is determined for poly(TPAp-DCBp). When the D-A junction is varied from para to meta,wenote that the hole and electron distributions are becoming more and more discrete.With poly(TPAm-DCBm) as an example,the S 1 hole and S 1 electron are independently centered on TPAand DCB, respectively,leading to adecreased S m index of 0.0321.…”

Sensing Mechanism of Excited‐State Intermolecular Hydrogen Bond for Phthalimide: Indispensable Role of Dimethyl Sulfoxide

“…In addition, we analyzed the electron density difference (EDD) between the first singlet excited‐state and the ground‐state for PTI, PTI‐DMSO and CORM3‐green, to investigate the changes in the electronic excitation process. [ 64‐65 ] The green and blue regions in Figure 5 indicate the difference in electron density corresponding to the S 1 → S 0 transition. As illustrated in Figure 6, the changes were mainly concentrated in the fluorophore part in PTI and PTI‐DMSO where fluorescence emission could occur.…”