Chemistry builds up from the idea that molecular structure determines the chemical and physical properties of matter. This principle guides the modern design of molecules for medicine, agriculture, and energy applications. However, chemical design principles have mostly remained elusive for emerging quantum technologies that exploit the fleeting but transformative properties of quantum coherence responsible for the wave-like interference of microscopic particles. Specifically, currently, it is not understood how chemical structure should be modified to rationally modulate quantum coherence and its loss. To leverage Chemistry's ability to build complex molecular architectures for the development of nextgeneration quantum technologies, there is a critical need to identify methods to tune quantum coherences in molecules and better protect them from quantum noise (or decoherence) that arises due to uncontrollable interactions of the molecular degrees of freedom of interest with its quantum environment. Protecting and manipulating molecular coherences is also necessary to unshackle chemical processes from the constraints of thermal Boltzmann statistics, as needed to enhance molecular function through coherence, develop novel routes for the quantum control of chemical dynamics, and the design of optical spectroscopies with enhanced resolution capabilities. In particular, electronic coherences generated by photoexcitation with ultrafast laser pulses in singlemolecules and molecular arrays have received widespread attention. These coherences dictate the photoexcited dynamics of molecules and, as such, play a pivotal role in our elementary description of photochemistry, photophysics, charge and energy transport, and in our understanding of vital processes such as photosynthesis and vision. These coherences decay on ultrafast (femtosecond) timescales due to the interaction of the electronic degrees of freedom with intramolecular vibrational modes and solvent. Despite considerable experimental and theoretical efforts to study electronic decoherence in molecules , its basic chemical principles are still not understood. For instance, how does electronic coherences in, say, the DNA base thymine decohere in water? How do the different vibrations in the molecule and solvent contribute to the overall coherence loss and which one is dominant? How do chemical functionalization and isomerism influence the different contributions to the overall decoherence? Addressing these basic questions requires a general strategy to connect chemical structure of both molecule and solvent to quantum decoherence phenomena.