Rational design of bright near- and shortwave-infrared (NIR: 700-1000 SWIR: 1000-2000 nm) molecular and nanoscale emitters is a fundamental for applications ranging from deep tissue imaging to telecommunications to energy harvesting. currently all reported organic chromophores with energy gaps in the SWIR have extremely low quantum yields (Φ<sub>F</sub>≤ 0.03). To address this, we describe a fundamental relationship between narrow energy gaps and emission quantum yield in molecular chromophores of the polymethine dye family by evaluating the radiative and non-radiative rates of 21 polymethine NIR/SWIR emissive chromophores. Using often ignored energy gap laws, a semi-empirical model demonstrates that the precipitous decline of Φ<sub>F</sub> in the SWIR is consistent with the combination of decreased radiative rates due to shrinking singlet energy gaps and increased nonradiative deactivation via high frequency vibrations. We develop a simple model that enables comparison of quantum yields among NIR/SWIR chromophores independent of the differences of the molecular energy gaps. We use this to see if different synthetic modifications to the dyes cause improvements in other photophysical properties. We hypothesize design principles that could affect radiative and nonradiative pathways. we thus guide synthetic chemists on rationally approaching the design of higher quantum yield chromophores viable for shortwave infrared fluorescence imaging.

How to improve shortwave infrared fluorescence quantum yields? Lessons from energy gap laws

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.