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Abstract The thermal conductivity of many materials depends on temperature due to several factors, including variation of heat capacity with temperature, changes in vibrational dynamics with temperature, and change in volume with temperature. For proteins some, but not all, of these influences on the variation of thermal conductivity with temperature have been investigated in the past. In this study, we examine the influence of change in volume, and corresponding changes in vibrational dynamics, on the temperature dependence of the thermal conductivity. Using a measured value for the coefficient of thermal expansion and recently computed values for the Grüneisen parameter of proteins we find that the thermal conductivity increases with increasing temperature due to change in volume with temperature. We compare the impact of thermal expansion on the variation of the thermal conductivity with temperature found in this study with contributions of heat capacity and anharmonic coupling examined previously. Using values of thermal transport coefficients computed for proteins we also model heating of water in a protein solution following photoexcitation. 

Optically excited heme proteins release their energy into the hydration water in approximately 7 ps, subsequent to internal vibrational redistribution. Adapted from an image created by S.Duce. 

Elucidating the nature of intramolecular vibrational energy redistribution (IVR) can guide the design of molecular wires. The ability to steer these processes through a mechanistic understanding of IVR is assessed by utilizing two-dimensional infrared (2D IR) spectroscopy. 2D IR spectroscopy allows for the direct investigation of timescales of energy transfer within three aromatic molecular scaffolds: 4′-azido-[1,1′-biphenyl]-4-carbonitrile (PAB), 2′-azido-[1,1′-biphenyl]-4-carbonitrile (OAB), and 4′-(azidomethyl)-[1,1′-biphenyl]-4-carbonitrile (PAMB). Energy transfer pathways between azido (N3)- and cyano (CN)-vibrational reporters uncover the importance of Fermi resonances, anharmonic coupling, and specific structural components in directing energy flow. Among these systems, PAB exhibits the fastest energy transfer (22 ps), facilitated by its co-planar biphenyl structure, enabling strong π–π stacking interactions to optimize vibrational coupling. In contrast, OAB demonstrates a moderate IVR timescale (38 ps) due to an orthogonal molecular plane and steric hindrance, which disrupts coupling pathways. PAMB, with a para-methylene group, introduces a structural bottleneck that significantly impedes energy flow, slowing down the energy transfer to 84 ps. The observed IVR rates align with computational predictions, highlighting intermediate ring modes in PAB as efficient energy transfer bridges, a mechanism that is less pronounced in OAB and PAMB. This study demonstrates that IVR is dictated not only by anharmonic coupling strengths but also by the extended alignment of vibrational modes across molecular planes and their delocalization within aromatic scaffolds. By modulating structural features, such as steric constraints and π–π interactions, we provide a framework for tailoring energy flow in conjugated molecular systems. These findings offer new insights into IVR dynamics for applications in molecular electronics.