Study On Photophysical Properties Of A New Type Of Linear And Star-shaped Oligomers

Organic photoelectric materials have many characteristics, such as all kinds ofcompounds, structural diversity, simple production process, easy film, photoelectricstable performance, low cost and so on. Now they have been widely used in organiclight-emitting diode (OLED), organic solar cells, organic field-effect transistors andother fields. Fluorene has high light stability and thermal stability. It also has highfluorescence quantum efficiency in solid state. Because its structure is easy to bemodified, we can increase the solubility and enhance the chemical reaction activity.Therefore the research based on fluorene monodisperse oligomers of luminescentmaterial aroused people’s great interest. In this thesis, we make the synthesis offluorene monodisperse functional oligomer as a starting point, and make linearoligofluorene An-OFVn (n=1,2,3,4) and star-shaped oligofluorene Tr-OFVn(n=1,2,3,4) as the research object. By conducting the linear and nonlinear optical teston them, we intent to study their photophysical properties and influenced factors.Some results have been obtained and outlined below:1. A series of linear oligofluorene An-OFVn (n=1,2,3,4): By using steady-stateabsorption, steady transmission, time correlated single photon counting (TCSPC),two-photon fluorescence and femtosecond Z-scan technique, we can study the linearand nonlinear optical properties of the samples. By using density functional theory(DFT), we can analyse the electron transfer mechanism. We found that the absorptionbands red-shifted with increasing the number of fluorenevinylene units because of theenlargement of the conjugation. Meanwhile, the strong emission at ca.615nmassigned to the electronic transition of the excimer for An-OFV1can be detected.However, when the number of fluorene units in the arms reached four, the emission intensity of the excimer would be decreased significantly, suggesting that theformation of excimer can be suppressed with increasing the number offluorene-vinylene units linked in the9,10-positions of anthracene. The strategy of therestraint of the excimer formation will be helpful for the fabrication of novel organicphotoelectric materials with high fluorescence efficiency.2. A series of star-shaped oligofluorene Tr-OFVn (n=1,2,3,4): We study fluorescentlifetime by transient absorption and study nonlinear characteristics using two-photonfluorescence and opening Z-scan technique. We found that the one-photon absorptionand single-photon-induced emission bands red-shifted with increasing the number offluorene-vinylene units because of the enlargement of the conjugation. It wasinteresting that the conjugated oligomers without strong donor and acceptor unitsexhibited two-photon absorption properties. The two-photo absorption cross sectionvalues increased obviously with prolonging the arms. We deduced that the branchedstar-shaped configration favored for the high TPA cross sections of Tr-OFVn. Itprovided a new strategy to design functional materials with a large two-photonabsorption cross section.