Two novel acceptor-donor-acceptor (A-D-A) small molecules BSeT1 and BSeT2 containing dimesitylborane as an electron acceptor and selenopheno[3,2-b] thiophene and selenopheno[2,3-b] thiophene as electron donors linked through a thiophene pi-conjugated spacer were synthesized and characterized. Their photophysical and electrochemical properties were investigated. In particular, BSeT1 demonstrated that the presence of a conjugated selenopheno[3,2-b] thiophene causes a bathochromic shift of the absorption bands with respect to a cross conjugated selenopheno[2,3-b] thiophene in BSeT2. The fluorescence spectra of BSeT1 exhibited yellow emission at 516 and 543 nm, while BSeT2 showed blue emission peak of 468 nm. Also, the emission quantum efficiency of BSeT1 was determined to be up to 11% in THF. These compounds demonstrated red-shift emissions in their solid states compared to those in organic solvents. The optimized geometries of BSeT1 and BSeT2 were achieved by density functional theory (DFT) to examine their electronic structures, frontier molecular orbital (FMO) energy levels and electronic excitations. The comparisons illustrated that the theoretical data are well in alignment with the corresponding experimental results. In addition, the structure-property relationships of BSeT1 and BSeT2 were assessed.