Donor strength of commonly used conjugated building blocks in organic electronics were investigated with density functional theory. The donor molecules were coupled to thiophene-incorporated acceptor groups, and electronic structure calculations were performed for the energies of frontier orbitals, total charge on donors, and particle probability distribution. A novel approach is also developed to analyze the large set of data on frontier orbitals. The electron donating ability of a donor was determined by comparing the highest occupied molecular orbital energies of the calculated structures. The effect of selected acceptor group and chosen functional method were also investigated to accurately determine the donor strength of each conjugated building block. Ethylenedioxythiophene, propylenedioxythiophene, and triphenylamine derivatives were found to be best donors among the conjugated units investigated. Such a comparative analysis of donor strengths is believed to be useful for researchers in designing novel organic semiconductors for organic electronic applications.