Glutathione and Esterase Dual-Responsive Smart Nano-drug Delivery System Capable of Breaking the Redox Balance for Enhanced Tumor Therapy

We have expounded the unique molecular design architecture for efficient thermally activated delayed fluorescence (TADF) materials based on a donor-linker-acceptor-linker-donor (D-L-A-L-D) framework, which can be employed as predecessors of organic light-emitting diode (OLED) devices. Different from traditional donor-acceptor-type (D-A-type) TADF scaffolds, the D-L-A-L- D structural design avoids direct coupling amid the D and A fragments allowing the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) to be spatially separated. It results in a reduced overlap between HOMOs and LUMOs, thus realizing fairly a slight singlet-triplet energy gap (Delta EST) and higher photoluminescence quantum yield (phi). We revealed that manipulating a linker between D and A fragments in intramolecular charge transfer compounds is an auspicious approach for realizing small Delta EST. Herein, we report a group of organic electroluminescent D-L-A-L-D-type molecules with different electron-donating and electron-accepting moieties using density functional theory calculations and timedependent density functional theory calculations. Two types of linkers, the pi-conjugated phenylene (-C6H4-) and aliphatic alkyl chains or sigma-spacer (-CH2- and -CH2-CH2-), were exploited between D and A fragments. In principle, the conjugation in D-pi- A-pi-D-type molecules and hyperconjugation in D-sigma-A-sigma-D type molecules encourage the spatial separation of the HOMO- LUMO causing a reduction in the Delta EST. All the designed molecules show a blue-shift in the emission wavelengths (lambda em) over the directly linked parent molecules except DPA-DPS-C6H4 and BTPA-DPS-C6H4 which show a red-shift. Violet-blue to green-yellow (376-566 nm) lambda em was observed from all of the investigated molecules. Other important properties that affect the efficiency of emission quantum yields like frontier molecular orbital analysis, natural population analysis, electron excitation analysis, exciton binding energies, ionization potentials, electronic affinities, and reorganization energies of the designed molecules were also inspected. We are confident that our work will effectively give a straightforward and distinctive approach to building incredibly effective TADF-OLEDs and a new perspective on their structural design.