The study explores the decoupling of excitons from high-frequency vibrations in π-conjugated molecules, which are known to accelerate non-radiative losses and limit the performance of light-emitting diodes, fluorescent biomarkers, and photovoltaic devices. By combining broadband impulsive vibrational spectroscopy, first-principles modeling, and synthetic chemistry, the researchers uncover two design rules for decoupling excitons from high-frequency vibrations. First, when the exciton wavefunction has a substantial charge-transfer character with spatially disjoint electron and hole densities, high-frequency modes can be localized to either the donor or acceptor moiety, reducing their perturbation to the exciton energy and spatial distribution. Second, materials with participating molecular orbitals that have a symmetry-imposed non-bonding character can be selected, decoupling them from high-frequency vibrational modes that modulate π-bond order. The researchers exemplify these design rules by creating a series of spin radical systems that exhibit efficient near-infrared emission (680–800 nm) from charge-transfer excitons. These systems show substantial coupling to vibrational modes only below 250 cm⁻¹, frequencies that do not allow fast non-radiative decay, leading to a suppression of non-radiative decay rates by nearly two orders of magnitude compared to π-conjugated molecules with similar bandgaps. The results demonstrate that losses due to coupling to high-frequency modes need not be a fundamental property of these systems.The study explores the decoupling of excitons from high-frequency vibrations in π-conjugated molecules, which are known to accelerate non-radiative losses and limit the performance of light-emitting diodes, fluorescent biomarkers, and photovoltaic devices. By combining broadband impulsive vibrational spectroscopy, first-principles modeling, and synthetic chemistry, the researchers uncover two design rules for decoupling excitons from high-frequency vibrations. First, when the exciton wavefunction has a substantial charge-transfer character with spatially disjoint electron and hole densities, high-frequency modes can be localized to either the donor or acceptor moiety, reducing their perturbation to the exciton energy and spatial distribution. Second, materials with participating molecular orbitals that have a symmetry-imposed non-bonding character can be selected, decoupling them from high-frequency vibrational modes that modulate π-bond order. The researchers exemplify these design rules by creating a series of spin radical systems that exhibit efficient near-infrared emission (680–800 nm) from charge-transfer excitons. These systems show substantial coupling to vibrational modes only below 250 cm⁻¹, frequencies that do not allow fast non-radiative decay, leading to a suppression of non-radiative decay rates by nearly two orders of magnitude compared to π-conjugated molecules with similar bandgaps. The results demonstrate that losses due to coupling to high-frequency modes need not be a fundamental property of these systems.