π-Extended Hexapyrrolylbenzenes: Exploring Charge-Transfer Phenomena in Donor-Acceptor Propellers

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Hexapyrrolylbenzenes (HPBs) are propeller-shaped molecules with potential applications in organic electronics.
• Understanding charge-transfer (CT) dynamics in donor-acceptor systems is crucial for designing functional materials.

Purpose of the Study:

• To design and synthesize novel propeller-shaped donor-acceptor hexapyrrolylbenzenes (HPBs).
• To investigate the photophysical properties and charge-transfer characteristics of these HPBs.
• To explore the role of molecular geometry and substituent effects on CT emission.

Main Methods:

• Synthesis of HPBs via nucleophilic substitution of hexafluorobenzene with π-extended pyrroles.
• Density Functional Theory (DFT) calculations to determine molecular geometry and electronic structure.
• Steady-state and time-resolved photophysical measurements (absorption, emission, fluorescence lifetime).

Main Results:

• Four HPB hybrids with varying electron-rich and electron-poor acenaphthylene-fused pyrroles were successfully synthesized.
• DFT calculations confirmed propeller-shaped geometries and spatial separation of frontier molecular orbitals.
• Photophysical studies revealed charge-transfer (CT) emission strongly dependent on solvent polarity, with the primary pathway involving ortho-positioned donor-acceptor pairs.

Conclusions:

• The synthesized HPBs exhibit efficient intramolecular charge transfer, making them promising candidates for optoelectronic applications.
• The propeller-like structure and specific arrangement of donor-acceptor units facilitate efficient CT emission.
• Excited-state dynamics, including acceptor bending, play a critical role in the observed charge-transfer pathway.