Another promising way to store solar energy for electricity and heat production is a so called ‘molecular solar thermal system’ (MOST). With this approach a molecule is converted by photoisomerization into a higher-energy isomer. Photoisomerization is a process in which one (cis-trans) isomer is converted into another by light( solar energy). This isomer is capable of storing the solar energy until the energy is released by a heat trigger or catalyst (than the isomer is converted into its original isomer). A promising candidate for such a MOST are Norbornadienes (NBD). This is because there is a high energy difference between the NBD and the quadricyclane (QC) photoisomer. This energy difference is approximately 96 kJ/mol. It is also known that for such systems, the donor-acceptor substitutions provide an effective means for redshifting the longest-wavelength absorption. This improves the solar spectrum match.