Uejima Motoyuki, Sato Tohru, Yokoyama Daisuke, Tanaka Kazuyoshi, Park Jong-Wook
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
Phys Chem Chem Phys. 2014 Jul 21;16(27):14244-56. doi: 10.1039/c4cp01428f. Epub 2014 Jun 10.
A theoretical design principle for enhancement of the quantum yield of light-emitting molecules is desired. For the establishment of the principle, we focused on the S1 states of blue-emitting anthracene derivatives: 2-methyl-9,10-di(2'-naphthyl)anthracene (MADN), 4,9,10-bis(3',5'-diphenylphenyl)anthracene (MAM), 9-(3',5'-diphenylphenyl)-10-(3'',5''-diphenylbiphenyl-4''-yl) anthracene (MAT), and 9,10-bis(3''',5'''-diphenylbiphenyl-4'-yl) anthracene (TAT) [Kim et al., J. Mater. Chem., 2008, 18, 3376]. The vibronic coupling constants and transition dipole moments were calculated and analyzed by using the concepts of vibronic coupling density (VCD) and transition dipole moment density (TDMD), respectively. It is found that the driving force of the internal conversions and vibrational relaxations originate mainly from the anthracenylene group. On the other hand, fluorescence enhancement results from the large torsional distortion of the side groups in the S1 state. The torsional distortion is caused by the diagonal vibronic coupling for the lowest-frequency mode in the Franck-Condon (FC) S1 state, which originates from a small portion of the electron density difference on the side groups. These findings lead to the following design principles for anthracene derivatives with a high quantum yield: (1) reduction in the electron density difference and overlap density between the S0 and S1 states in the anthracenylene group to suppress vibrational relaxation and radiationless transitions, respectively; (2) increase in the overlap density in the side group to enhance the fluorescence.
需要一种提高发光分子量子产率的理论设计原则。为了确立这一原则，我们聚焦于蓝色发光蒽衍生物的S1态：2-甲基-9,10-二(2'-萘基)蒽(MADN)、4,9,10-双(3',5'-二苯基苯基)蒽(MAM)、9-(3',5'-二苯基苯基)-10-(3'',5''-二苯基联苯-4''-基)蒽(MAT)和9,10-双(3''',5'''-二苯基联苯-4'-基)蒽(TAT)[Kim等人，《材料化学杂志》，2008年，18卷，3376页]。分别利用振动耦合密度(VCD)和跃迁偶极矩密度(TDMD)的概念计算并分析了振动耦合常数和跃迁偶极矩。发现内转换和振动弛豫的驱动力主要源于蒽烯基。另一方面，荧光增强源于S1态侧基的大扭转畸变。这种扭转畸变是由弗兰克-康登(FC) S1态中最低频率模式的对角振动耦合引起的，它源于侧基上一小部分电子密度差。这些发现引出了以下关于具有高量子产率的蒽衍生物的设计原则：(1)降低蒽烯基中S0和S1态之间的电子密度差和重叠密度，分别抑制振动弛豫和无辐射跃迁；(2)增加侧基中的重叠密度以增强荧光。
