New $pi$-conjugated multi-branched molecules were synthesized through the Homer-Emmons reaction using alkyl-substituted, 3,4-ethylenedioxythiophene-based, thiophenyl aldehydes and octaethyl benzene-l,2,4,5-tetrayltetrakis(methylene) tetraphosphonate as the core unit; these molecules have all been fully characterized. The two multi-branched conjugated molecules exhibited excellent solubility in common organic solvents and good self-film forming properties. The semiconducting properties of these multi-branched molecules were also evaluated in organic field-effect transistors (OFET). With octyltrichlorosilane (OTS) treatment of the surface of the $SiO_2$ gate insulator, two of the crystalline conjugated molecules, 7 and 8, exhibited carrier mobilities as high as $2.4({pm}0.5){ imes}10^{-3}$ and $1.3({pm}0.5){ imes}10^{-3}cm^2V^{-1}s^{-1}$, respectively. The mobility enhancement of OFET by light irradiation ($lambda$ = 436 nm) supported the promising photo-controlled switching behavior for the drain current of the device.