Unraveling the Role of Triplet–Triplet Annihilation and Photodegradation in Difluoroboron‐Based Organic Laser Gain Materials

TL;DR

This study explores how light emission in certain organic laser materials is caused by specific energy transfer processes and how these materials degrade under light exposure.

Contribution

The study reveals that amplified spontaneous emission in difluoroboron-based materials originates from aggregated singlet states, not phosphorescence, and identifies triplet–triplet annihilation as the key mechanism.

Findings

Emission in difluoroboron-based materials is primarily from singlet states via triplet–triplet annihilation-driven delayed fluorescence.

Amplified spontaneous emission arises from aggregated singlet states rather than triplet states.

Photodegradation introduces new fluorescence and phosphorescence bands, complicating the material's photophysics.

Abstract

In this study, we investigate the triplet exciton dynamics of a series of difluoroboron‐based organic gain molecules. We synthesized three previously reported molecules from the difluoroboron family and examined their photophysical properties using time‐resolved emission spectroscopy and high‐level theoretical calculations. Our results reveal that emission from these materials arises predominantly from the singlet manifold via prompt and triplet–triplet annihilation (TTA)‐driven delayed fluorescence, rather than from phosphorescence, challenging the earlier assumptions of amplified spontaneous emission (ASE) originating from the triplet manifold. In highly concentrated solutions, the emission shows strong resemblance to that of the crystalline phase, confirming its origin from aggregate singlet states rather than monomeric pathways. Further, the materials are prone to photodegradation, which gives rise to new high‐energy fluorescence and phosphorescence bands adding to the complexity of the photophysics of this family of materials.

Amplified spontaneous emission (ASE) in difluoroboron‐based gain molecules is shown to originate from aggregated singlet states (S1), contradicting its previously assumed phosphorescent origin. Additionally, the delayed emission arises from a triplet–triplet annihilation upconversion (TTA‐UC) mechanism rather than a thermally activated (TADF) process, with rapid photodegradation further complicating the excited‐state dynamics and emphasizing the need for improved molecular design.

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