Two diaryl porphyrin isomers have been analyzed using Raman and resonance Raman, electronic absorption,1HNMR spectroscopies coupled with density functional theory approaches. Despite similar nature, these isomers exhibit distinct experimental signatures, which in each case have be simulated by computational methods. Porphyrin saddling may explain the variations seen experimentally, where the degeneration of frontier molecular orbitals occurs. Optical interaction is observed from the aldehyde moiety with contribution to LUMO and LUMO+2 orbitals; and is confirmed by resonance Raman spectroscopy. Configuration interaction is modulated as a function of aldehyde position, resulting in 20% variation of the Q:B ratio from 0.144 to 0.114.