Degree-Based Topological Descriptors and Physicochemical Structure–Property Trends in Oligothiophene Derivatives
Mohammed Alsharafi *
Department of Mathematics, Faculty of Arts and Science, Yildiz Technical University, Istanbul 34220, Turkey and Department of Mathematics, Faculty of Science, Sana’a University, Sana’a, Yemen.
Yusuf Zeren
Department of Mathematics, Faculty of Arts and Science, Yildiz Technical University, Istanbul 34220, Turkey and Department of Statistics, Istanbul Ticaret University, Istanbul, Turkiye.
Abdu Alameri
Department of Biomedical Engineering, Faculty of Engineering, University of Science and Technology, Yemen.
*Author to whom correspondence should be addressed.
Abstract
This study presents a graph-theoretical and descriptive structure–property analysis of the linear \(\alpha\)-linked oligothiophenes
bithiophene, terthiophene, quaterthiophene, sexithiophene, and octithiophene. From the common edge partition of their
hydrogen-suppressed molecular graphs, explicit closed forms are derived for fourteen degree-based descriptors: the first and second Zagreb, forgotten, Yemen, first and second hyper-Zagreb, three redefined Zagreb, Randi´c, Sombor, Yemen–Sombor, geometric–arithmetic, and atom–bond connectivity indices. Numerical values are obtained for all five molecules. Ten physicochemical endpoints reported in PubChem—polar surface area, molecular weight, complexity, XLogP3-AA, heavy-atom count, boiling point, enthalpy of vaporization, flash point, molar refractivity, and molar volume—are analyzed using descriptive linear regression. Every considered index is an affine function of oligomer length; therefore, the fourteen univariate regressions have identical fitted values and goodness-of-fit statistics for a fixed endpoint, although their slopes and intercepts differ. To avoid redundant reporting, the main text provides a compact endpoint-level summary and one representative index model, while all 140 descriptor–endpoint equations are supplied in the supplementary material. The models describe trends within this five-member homologous series and are not presented as externally validated predictive QSPR models.
Keywords: Oligothiophenes, degree-based topological indices, PubChem, structure–property relationship, linear regression, descriptor collinearity