The trans-to-cis isomerization reduces the distance between the two Ca atoms by almost one third of its initial value (see Fig. ). Thus, we expect to observe a response to the isomerization in the OCCs optical properties. Table shows the change in the excitation energy upon isomerization. In contrast to pAB, bpAB shows a much more appreciable change in the excitation energy. CaO-azobenzene can be produced by reacting the precursor ligand 4-hydroxyazobenzene (trans form purchased from Sigma Aldrich) with metastable Ca atoms generated from laser ablation in a cryogenic buffer gas cell, as previously discussed in the context of the production of CaOC 6 H 4 molecules and their functionalized derivatives . However, initial experiments have revealed that the yellow powder of 4-hydroxyazobenzene undergoes a color change to black at ∼ 100 • C, well below its melting point of 155 • C. This suggests the thermal decomposition of azobenzene 140 , making it unlikely to generate sufficient precursor vapors for the reaction. To address this issue, the precursor can be functionalized with electronwithdrawing groups, such as fluorine atoms, to enhance its thermal stability 140 . Alternatively, a solid-phase method 79 can be adopted. A mixture of CaH 2 and precursor powder (1:1 molar ratio), with polyethylene glycol or silver powder as a binder, can be thoroughly mixed and ground before being pressed into a pellet for direct laser ablation. Preliminary results with the Sr-equivalent have shown two peaks in the excitation spectra. Further experiments of using CaH 2 and precursor to produce CaO-azobenzene will be performed. In addition, the precursor ligand only exists in the trans isomeric form, enabling photoswitching to the cis isomer upon laser illumination. Specifically, the precursor 4-hydroxybenzene has been reported to undergo photoswitching at ∼ 360 nm (3.44 eV) . A 360 nm UV LED or pulsed Nd:YAG laser at 355 nm (3.49 eV) can be employed to initiate the photoswitching process of CaO-azobenzene. To measure the branching ratios of the X → A and X → B transitions of these molecules, dispersed laser-induced fluorescence (DLIF) spectroscopy can be taken either with a pulsed dye laser used in the previous works , or with a continuous-wave (CW) dye laser which is currently under installation in our lab. The narrow line-width and the broad scanning range of the CW dye laser allow us to significantly suppress the background noise and enable us to obtain high-resolution spectra of these azobenzene molecules.