Highly accurate quantum chemical calculations were used in a comparative study of the pi-conjugation length and CH/N heterosubstitution effects on the structure and a number of properties of tris(o-phenylenedioxy) cyclotrisphosphazene (TPP) derivatives to identify the role of each of them in the modulation of the host...guest complex stability and available space for the adsorbate within TPP-like organic zeolite (OZ). From the BH&HLYP/6-31G(d,p) structures it was found that extending the side fragment with a phenyl ring and substituting CH/N preserve the "paddle wheel" molecular shape, a key factor in the tunnel formation on which the organic zeolite use of TPP is based on. Compared to the unsubstituted molecules, the side fragment is shortened for CH/N heterosubstitution, which may decrease the diameter of the tunnel. In addition, through accurate ionization potential (IP) calculations (at the HF/6-311 + G(d) level) the electron-donor (E-D) capacity was found to be more significantly enhanced by a lateral than a linear extension with phenyl ring, while it decreased upon CH/N heterosubstitution, which can affect the stability of some related host...guest complexes in the same order. Finally, as recently reported for TPP, the current results based on PBE0/6-31G(d,p) show that upon release of an electron the structural stability may not be altered by a CH/N mono- or disubstitution. From these features it was concluded that if the crystal requirement can be attained clathrates of good tolerance toward guest molecules in a wide range of Lewis acidity with variable E-D strength and available space for adsorbates may be reasonably awaited by exploiting these two approaches.