The practical realization of smart optical filters, i.e. devices which change their optical transmission in a suitable way to keep a working state for a general light sensitive element, can involve the use of conjugated molecules whose light absorption properties are light-intensity dependent (nonlinear optical effect). The verification of optical limiting displayed by some particular conjugated molecules, e.g. phthalocyanines, is quite noteworthy and can be successfully exploited for the realization of such smart optical devices. In the present contribution the analysis of the relevant molecular feature of a phthalocyanine are analyzed with the aim of determining useful correlations between optical limiting performance and phthalocyanine chemical structure. In particular, the electronic nature of the substituent is considered as a key factor for the explanation of some observed optical limiting trends.