The State Key Laboratory of Molecular Reaction Dynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China.
J Phys Chem B. 2010 Sep 16;114(36):11737-45. doi: 10.1021/jp104868j.
We report a series of stiff dendrimers (referred to as T1, T2, T3, and T4) that have both gigantic two-photon absorption (TPA) cross sections up to 25,000 GM and strong two-photon excited fluorescence (TPEF) with fluorescence quantum yield of ∼0.5. The large TPA cross sections and high quantum yields of these dendrimers are directly related to their geometrical structures, where the polycyclic aromatic pyrene is chosen as the chromophoric core because of its planar and highly π-conjugated structure, fluorene moieties as dendrons extend the conjugation length through the planar structure, and carbazole moieties are modified at three-, six-, and nine-positions as electron donor. All of these groups are linked with acetylene linkage for effective π-electron delocalization, leading to large TPA cross section and high fluorescence quantum yield. The spectral properties of all dendrimers are investigated by one- and two-photon excitations. Furthermore, steady-state fluorescence excitation anisotropy and quantum chemical calculation are also employed to determine the structure-related mechanism of these dendrimers with gigantic TPA cross sections and high TPEF efficiency. We then show that the improvement of branched chains in the T-series dendrimers enhances the light-harvesting ability. The core emission spectra, fluorescence quantum yield, and fluorescence lifetime are almost invariable by directly exciting the dendrons. These results will provide a guideline for the design of useful two-photon materials with structural motifs that can enhance the TPA cross-section and fluorescence quantum yield of a molecule without causing a red shift of the one- and two-photon excitation wavelengths for specific applications.
我们报道了一系列僵硬的树枝状大分子（分别称为 T1、T2、T3 和 T4），它们具有高达 25000 GM 的巨大双光子吸收（TPA）截面和强双光子激发荧光（TPEF），荧光量子产率约为 0.5。这些树枝状大分子的大 TPA 截面和高量子产率与它们的几何结构直接相关，其中多环芳烃芘因其平面和高度π共轭结构而被选为发色团核心，芴部分作为树枝状大分子通过平面结构扩展共轭长度，咔唑部分则在三、六和九位置被修饰为电子供体。所有这些基团都通过乙炔键连接，以实现有效的π电子离域，从而导致大的 TPA 截面和高的荧光量子产率。所有树枝状大分子的光谱性质都通过单光子和双光子激发进行了研究。此外，稳态荧光激发各向异性和量子化学计算也被用于确定这些具有巨大 TPA 截面和高 TPEF 效率的树枝状大分子的结构相关机制。然后我们表明，T 系列树枝状大分子中支链的改进增强了光捕获能力。通过直接激发树枝状大分子，核心发射光谱、荧光量子产率和荧光寿命几乎不变。这些结果将为设计具有结构基序的有用双光子材料提供指导，这些结构基序可以在不引起单光子和双光子激发波长红移的情况下增强分子的 TPA 截面和荧光量子产率，从而满足特定应用的需求。
