Molecular structure and electronic properties of porphyrin-oligothiophene-perylene using quantum chemical calculation

Abstract

A new series of compounds consisting of porphyrin (Por) molecule linked to perylene (Per) unit via a thiophenic bridge are designed, namely, Por-Per, Por-Thio-Per, Por-2Thio-Per, and Por-3Thio-Per by varying the number of thiophene ring from 0 to 3, respectively. Structural and electronic properties of those compounds were studied using quantum calculation approach. The method used was validated and found that the B3LYP/6-31G(d) is the optimal one compromising between the accuracy and the computer time required. With optimal structure of Por-Thio-Per, the effect of mono- and bi-substituents R on C3 and R on C4 of thiophene ring was studied. It was shown that significant changes of the torsion angle between the molecular planes of the Por and Per rings were found only for the two bi-substituted derivatives, R = R = OCH3 and NH2, and one mono-substituted derivative, R = H and R = NH2. Noticeable decreases of the HOMO-LUMO energy gap were found only when the mono-substituents are the electron donor groups. In addition, The significant change of the HOMO-LUMO energy gap was also observed as the function of number of thiophene ring. The UV-visible spectra of all proposed compounds cover a broader range, 370-730 nm and characteristics of the Por and Per molecules, which indicate by the absorptions spectra at 372 and 473 nm, remain unchanged.