Fluorescence properties of 36 specially chosen aromatic compounds are experimentally studied at a temperature of 293 K. The compounds are arranged in pairs so that even numbered compounds, because of symmetrical substitutions, are designated a higher symmetry group than those of odd numbered compounds. The pairs are, however, family-related in n-structure. The quantum yield of fluorescence 7, and decay times zf, of deaerated and nondeaerated cyclohexane solutions are measured. The oscillator strength fe, the fluorescence rate constants Kf, natural lifetimes z0 T and intersystem crossing rate constants/(st, are calculated. Investigations showed that transition from a lower to higher symmetry, but family-related in n-structure molecule depending on the nature of the S ~ excited state, has different effects on parameters such as ?, zf, fe, Kr and Kst. If the S 1 excited state has the nature of the Sp(~La) state, then the value of Voo decreases. This is accompanied by an increase in the values of ~, and Zr. Parameters f~ and Kf may change unpredictably. However, if the development of n-structure occurs in the direction of polarization of the So ~ S t transition, the values of J~ and consequently Kf are also found to increase. If the S ~ excited state has the nature of the S,(1Lb) state then generally, y, fe and Kf are found to decrease, with "t'f increasing. Furthermore, the /(st value in most cases of symmetrical substitution, decreases, sometimes very significantly, though the energy gap between S ~ and T~ states becomes less. For example, the transition from 9-phenylanthracene ((72 symmetry group)to 9,10-diphenylanthracene (D2 symmetry group) is accompanied by a decrease in the value of Kst, by a factor of 18. This phenomenon is qualitatively treated using the first-order spin-orbit coupling theory and simulation of singlet and triplet levels.