Substituent Effects on Photophysical Properties of N-Thienylcarbazoles

The electronic and photophysical properties of a series of N-thienylcarbazoles were first clarified and compared to one another.The characters of both ground and excited states of carbazole moiety are much more affected by a 2-thienyl group than a 3-thienyl group.Carbazole and thiophene are important heteroaromatic compounds from the aspects of constructing functional materials such as organic light-emitting materials, photoconductors, and so on. 1 For instance, these heterocycles have been used as building-blocks for hole-transport and light-emissive materials or host materials for triplet emitters in OLEDs. 2,3As one of the most fundamental compounds containing carbazole and thiophene, N-(2-thienyl)carbazole (2) has been prepared, 4 but its photophysical properties are unknown.2,5-Bis(N-carbazolyl)thiophene ( 3) is also known in the literature, 5 but its photophysical properties are not clarified, although those of 5,5'-bis(N-carbazolyl)-2,2'-bithiophene are disclosed. 6rprisingly, N-(3-thienyl)carbazole (1) has been unknown in the literature.Thus, we were prompted to investigate and compare the electronic and photophysical properties of 1-3 systematically.As a result, we have found that their photophysical properties remarkably depend on the substitution positions of thiophene.