Oligothiophene dendrimers as new building blocks for optical applications

Thiophene branched structures have been proposed as candidates for photon harvesting and electron-hole transporting materials in novel organic light emitting diodes and solar energy conversion devices. To understand the photoinduced processes in a novel thiophene dendrimer system, the excited state dynamics and nonlinear optical properties of 3D oligothiophene dendrimers have been investigated. The key point of this contribution is that we have found that with these thiophene dendrimer systems, the excitation is delocalized over a large number of thiophene units in the dendrimer and there is an ultrafast energy transfer (200-300 fs) to the longest branch of dendrimer, which can be utilized for future optical devices. In terms of nonlinear optics, it was found that a super-linear increase of two-photon absorption cross-section is observed with an increase in thiophene dendrimer generation that can be explained by the increased excitation delocalization. Generation dependent torsional energy redistribution has also been observed, which planarizes the final emissive state on a picosecond time scale.