A single isomer rotary switch demonstrating anti-Kasha behaviour: Does acidity function matter?

Area of Science:

• Molecular switches
• Supramolecular chemistry
• Photochemistry

Background:

• Hydrazone-based molecular switches often suffer from disadvantages related to competitive proton acceptor sub-rotors.
• Designing switches with specific functionalities is crucial for controlling molecular behavior.

Purpose of the Study:

• To design and synthesize a novel rotary switch that overcomes the limitations of existing hydrazone-based systems.
• To investigate the photophysical properties and proton transfer dynamics of the newly designed switch.

Main Methods:

• Synthesis of a novel molecular compound featuring a pyridyl ring and a carboxylic acid (COOH) group as sub-rotors.
• Spectroscopic analysis to determine the ground-state isomer and investigate excited-state properties.
• Study of excited-state intramolecular proton transfer (ESIPT) phenomena.

Main Results:

• The designed rotary switch exhibits a single isomer in the ground state due to the engagement of the pyridyl nitrogen atom.
• The presence of acidic functionality facilitates excited-state intramolecular proton transfer (ESIPT).
• The observed ESIPT behavior demonstrates anti-Kasha characteristics.

Conclusions:

• A novel and effective molecular rotary switch has been successfully designed.
• The switch's unique structure enables controlled proton transfer and exhibits interesting photophysical properties.
• This work offers a new platform for developing advanced molecular switches with tailored functionalities.