Abstract
Two new triarylborane-based o,o'-substituted 2,2'-bithienyls, BT-BNMe (2) and BT-BNBn (2) , which contain BMes(2) and NMe(2)/NBn(2) groups at the 3,3'-positions, have been synthesized. Similar to the o,o'-substituted biphenyl analogues, BP-BNMe (2) and BP-BNBn (2) , which contain BMes(2) and NMe(2)/NBn(2) groups at the 2,2'-positions, the steric effect of the amino group has significant influence on the conformation of the 2,2'-bithienyl skeleton. The boryl and amino groups are located at the same side of 2,2'-bithienyls axis with a short B···N distance (3.63 Å) for the NMe(2)-substituted BT-BNMe (2) . On the contrary, the two substituents are arranged on the two different sides of the 2,2'-bithienyls axis for BT-BNBn (2) , which is modified with bulky NBn(2). Despite the remarkable differences in the steric structure, the two 2,2'-bithienyls display fluorescence at close wavelengths, which is in sharp contrast to the much red-shifted fluorescence of BP-BNMe (2) than BP-BNBn (2) . The theoretical calculations demonstrated that the two 2,2'-bithienyls have close highest occupied molecular orbital-lowest unoccupied molecular orbital gaps in the excited state, which firmly support the experimental results. Thus, the parent main chain framework can exhibit great impact on the charge-transfer emission of o,o'-substituted biaryls.