Impact of Host–Emitter Interactions on Light Amplification in Laser Dyes

Organic lasers hold great promise for enabling a new class of future optoelectronics. Consequently, the development of new organic semiconductors as gain media has recently been the subject of significant interest. The molecular design principle based on Einstein coefficients has been validated for achieving high gain, with para-phenylene-vinylene scaffolds recognized as one of the most crucial frameworks. In this study, we develop a stilbene tetramer derivative, QSBCz, which has significantly increased conjugation compared to the highly efficient laser material, BSBCz, resulting in a remarkably high radiative decay rate and a large gain cross-section. However, we find that the optical losses play a significant role in the light amplification of QSBCz. Indeed, a comprehensive understanding and suppression of detrimental optical loss pathways throughout the lasing process are essential, whereas the losses intrinsically associated with molecules have not been well considered. Although host–guest systems are helpful in preventing concentration quenching in aggregated states, this study reveals notable losses when using common host molecules such as 4,4′-bis(9H-carbazol-9-yl)biphenyl (CBP) and mCBP. In contrast, a BSBCz derivative is successfully employed as the host, leading to improved stimulated emission amplification. These findings indicate the importance of host–emitter interactions in lasing properties and highlight the necessity to optimize host materials for developing new laser dyes.