Move aside pentacene: Diazapentacene doped para-terphenyl as a zero-field room-temperature maser with strong coupling for cavity quantum electrodynamics

Masers, the microwave analogue of lasers, promise to deliver ultra-low noise amplification of microwave signals for use in medical MRI imaging and deep-space communication. Research on masers in modern times was rekindled thanks to the discovery of gain media that were operable at room-temperature, eschewing bulky cryogenics that hindered their use. However, besides the two known materials of pentacene doped in para-terphenyl and negatively-charged nitrogen-vacancy defects in diamond, there has been scarce progress in the search for completely new room-temperature gain media. Here we show the discovery of 6,13-diazapentacene doped in para-terphenyl as a maser gain medium that can operate at room-temperature and without an external magnetic field. A measured maser pulse power of -10 dBm shows it is on par with pentacene-doped para-terphenyl in absolute power, while possessing compelling advantages against its pentacene predecessor in that it has a faster amplification startup time, can be excited with longer wavelength light at 620 nm and enjoys greater chemical stability from added nitrogen groups. Furthermore, we show that the maser bursts allow 6,13-diazapentacene-doped para-terphenyl to reach the strong coupling regime for cavity quantum electrodynamics, where it has a high cooperativity of 182. We study the optical and microwave spin dynamics of 6,13-diazapentacene-doped para-terphenyl in order to evaluate its behavior as a maser gain medium, where it features fast intersystem crossing and an advantageously higher triplet quantum yield. Our results pave the way for the future discovery of other similar maser materials and help point to such materials as promising candidates for the study of cavity quantum electrodynamic effects at room-temperature.