Developed in the 1930s, quantum mechanics remains at the heart of physical chemistry both as a working principle and as a quantitative theory. We are currently investigating two areas: (i) energy transfer and conversion in photosynthesis and (ii) quantum-classical correspondence. To achieve high efficiency in collecting and converting solar energy, photosynthetic systems take advantage of the interplay of quantum coherence, protein environments, and self-assembling structures. Understanding these natural processes in plants and bacteria provides key insights into the design of efficient and robust artificial light-harvesting systems. Employing classical trajectories for the optimal control of energy flow and the characterization of spectroscopic signatures of quantum coherence provides an intuitive means to develop these insights further. Related problems of interest include electron transfer, heat conduction in nano-wires, and vibrational energy transfer in dissipative ABA molecules.