Two different kinds of configurations of 1,4-bis[2-(4-pyridyl)ethenyl]-benzene(trans-bpeb and cis-bpeb) were achieved,and a bpeb dimer was synthesized in dimethyl sulfoxide(DMSO).Compared with the previous work that synthesized the bpeb dimer or polymer in crystal with a template agent needed,the reaction occurred in a solution phase in the present method.A hand-held ultraviolet lamp(365 nm) with the power of 12 W and the Watt density of 0.35 mW/cm2 can realize the photodimerization of bpeb,instead of the high-power mercury lamp in most previous studies.Unlike other 2+2 cycloaddition in liquid state using catalysts even noble metals,no catalysts were required here,which is cost-saving.Only the trans-pbeb can start the cycloaddition and the formation of the close J-aggregations of trans-pbeb in DMSO is a precondition for explaining the 2+2 photodimerization.The productivity for the 2+2 cycloaddition product was achieved as 55.6％.