Abstract: Weak interactions of molecules with solvents and/or environments are of crucial importance in material science and biology, but rather difficult to investigate quantitatively. Circular dichroism (CD) spectra reflect sensitively the conformational structures of chiral molecules, their (weak) interactions with solvents and/or proteins, etc. The SAC-CI method gives their CD spectra very reliably. From this fact, the SAC-CI method is a useful tool to investigate the conformational geometries of chiral molecules, their interactions with environments, etc by comparing their experimental and SAC-CI theoretical CD spectra. We initiated a systematic molecular technology, called ChiraSac (Chirality + SAC-CI) project (see Figure 1) by using the SAC-CI code and other highly reliable and useful codes on GAUSSIAN suit of programs. We have already applied this project successfully to several topics of chiral spectroscopy and photobiology . We will present here conformational dependence of Hydroxyphenylacetic Acid and similarities and differences between RNA and DNA, etc, as some recent applications of ChiraSac to chiral spectroscopy and photobiology.