Multi-colour and red emissions from a small donor-acceptor molecule by breaching Kasha's rule

Area of Science:

• Organic chemistry
• Photophysics
• Materials science

Background:

• Organic molecules can exhibit unique photophysical properties based on their structure.
• Controlling light emission from molecules is crucial for applications in organic electronics and sensing.
• The Kasha's rule typically describes fluorescence from the lowest excited singlet state (S1).

Purpose of the Study:

• To design and synthesize a small organic molecule capable of emitting multicolor and red light.
• To investigate the photophysical mechanisms underlying the observed light emission, specifically focusing on anti-Kasha effects.
• To explore the impact of donor-acceptor substituents on photoluminescence properties, including Stokes shifts and spectral overlap.

Main Methods:

• Synthesis of a small organic molecule (MW 260 Da) with specific donor-acceptor substituents.
• Photophysical characterization, including absorption and emission spectroscopy.
• Analysis of excited-state dynamics to confirm emission from S1 and S3 states.

Main Results:

• The synthesized molecule exhibits emission of multicolor and red light.
• Simultaneous anti-Kasha and donor-acceptor effects were observed, leading to emission from both S1 and S3 excited states.
• Introduction of donor-acceptor substituents resulted in large Stokes shifts (>5000 cm-1) with negligible spectral overlap.

Conclusions:

• A small organic molecule has been developed that emits multicolor and red light.
• The emission originates from two excited states (S1 and S3), defying Kasha's rule.
• The molecule's design with donor-acceptor substituents provides large Stokes shifts and minimal spectral overlap, suggesting potential for advanced optical materials.