Abstarct: In the first part of this research, molecular structures, vibrational frequencies and the chemical shifts of HNMR for series of chloro- derivaties of salicylideneaniline (Cl-SAN) were investigated using DFT calculations and then the result were compared with the analogous parameters of SAN. The effect of Cl atom on the intramolecular hydrogen bonding (IMHB) strength was studied by the natural bond orbital (NBO) analysis and quantum theory of atoms in molecules (QTAIM). The nature of H-bond was investigated using QTAIM parameters. It is shown, that the interaction of N‧‧‧H bond for these compounds is partially covalent in nature and so these compounds are classified on the system with medium H-bond. Comparison of the related parameters to H-BOND of these compounds showed, 11-Cl-SAN, which chloro was placed in ortho position respect to C=N group, has a strongest H-bond.m In the second part of this research, excited state reaction coordinate and the energy profiles of SAN and 11-Cl-SAN were studied at the CC2 level of theory using Turbomole package. The OH-form of the 11-Cl-SAN absorbs at 357 nm compared to 339 nm of SAN at the S0-S1 transition. So Cl- substitution in the redshift of this transition and although this shift is not so large, the Cl- substitution (11-Cl-SAN) is an effective idea for tuning the photophysical nature of 11-Cl-SAN and its similar system.