Toro Carlo, De Boni Leonardo, Yao Sheng, Ritchie James P, Masunov Artëm E, Belfield Kevin D, Hernandez Florencio E
Department of Chemistry, University of Central Florida, P.O. Box 162366, Orlando, Florida 32816-2366, USA.
J Chem Phys. 2009 Jun 7;130(21):214504. doi: 10.1063/1.3147011.
The photophysical properties of a symmetric squaryllium dye, namely, 2,4-bis[4-(N,N-dibutylamino)-2-hydroxyphenyl] squaraine (SQ), in its monomer form in acetone solution, have been thoroughly studied by means of one-photon absorption (1PA) and two-photon absorption (2PA), excitation anisotropy, fluorescence emission, fluorescence quantum yield, and excited state absorption. The results show that there is a strong one-photon allowed absorption band in the near IR region associated with intramolecular charge transfer. Higher one-photon allowed and forbidden singlet excited states were also revealed by absorption and excitation anisotropy. A relatively high fluorescence quantum yield (0.44) was measured for this dye. The nonlinear optical characterization of SQ in solution confirms the ability of squaraine dyes to be used as good two-photon absorbers. Additionally, it was found that this dye presents both saturable and reverse saturable absorption effects. Density functional theory calculations of the 1PA and 2PA electronic spectra of SQ were carried out to support the experimental data. A detailed analysis of the symmetry and energy of the orbitals involved in the lowest five electronic transitions is presented and discussed in relation to the behavior observed experimentally.
一种对称方酸染料，即2,4-双[4-(N,N-二丁基氨基)-2-羟基苯基]方酸菁（SQ），在丙酮溶液中以单体形式存在时的光物理性质，已通过单光子吸收（1PA）和双光子吸收（2PA）、激发各向异性、荧光发射、荧光量子产率以及激发态吸收等手段进行了深入研究。结果表明，在近红外区域存在一个与分子内电荷转移相关的强单光子允许吸收带。通过吸收和激发各向异性还揭示了更高的单光子允许和禁戒单重激发态。测得该染料的荧光量子产率相对较高（0.44）。溶液中SQ的非线性光学表征证实了方酸菁染料作为良好双光子吸收剂的能力。此外，发现该染料呈现出饱和吸收和反饱和吸收效应。对方酸菁1PA和2PA电子光谱进行了密度泛函理论计算，以支持实验数据。给出并讨论了与最低五个电子跃迁相关的轨道对称性和能量的详细分析，以及与实验观察到的行为的关系。
