Oligofluorenes as Polymeric Model Compounds for Providing Insight into the Triplets of Ketone and Ketylimine Derivatives

详细信息    查看全文

• 作者：Patricia Robert ; Andr茅anne Bolduc ; W. G. Skene
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：September 20, 2012
• 年：2012
• 卷：116
• 期：37
• 页码：9305-9314
• 全文大小：453K
• 年卷期：v.116,no.37(September 20, 2012)
• ISSN：1520-5215

文摘

A series of oligofluorenes ranging between one and three repeating units were prepared as structurally well-defined representative models of polyfluorenes. The photophysics of the oligofluorene models were investigated both by laser flash photolysis and steady-state fluorescence. The effects of the ketone and ketylimine functional groups in the 9-position on the photophysical properties, notably the triplet quantum yield (桅_TT) by intersystem crossing and the absolute fluorescence quantum yields (桅_fl), were investigated. The singlet depletion method was used to determine both the 桅_TT and molar absorption coefficients of the observed triplets (蔚_TT). Meanwhile, the absolute 桅_fl were determined using an integrating sphere. It was found that both the ketone and ketylimine substituents and the degree of oligomerization contributed to quenching the oligofluorene fluorescence. For example, the 桅_fl was quenched 5-fold with the ketylimine and ketone substituents for the bifluorenyl derivatives compared to their corresponding 9,9-dihexyl bifluorenyl counterparts. Meanwhile, the 桅_fl quenching increased 14 times with the trifluorenyl ketone and ketylimine derivatives. Measured 桅_TT values ranged between 22 and 43% for the difluorenyl derivatives with 蔚_TT on the order of 13鈥?00 cm^鈥? M^鈥?. The 桅_TT decreased to <10% concomitant with doubling of the 蔚_TT when the degree of oligomerization was increased to 3. A new fluorescence emission at 545 nm formed at low temperatures for the ketone and ketylimine oligofluorene derivatives. The emission intensity was dependent on the temperature, and it disappeared at room temperature.