Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission
Low-Temperature Luminescence in Organic Helicenes: Singlet versus Triplet State Circularly Polarized Emission
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DOI：
10.1021/acs.jpclett.2c03831
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发表时间：
2023-01-26
影响因子：
5.7
通讯作者：
Crassous, Jeanne
中科院分区：
文献类型：
--
作者：
Dhbaibi, Kais;Morgante, Pierpaolo;Crassous, Jeanne
报道了在低温（77 K）下对具有受电子（-CN、-py、-NO2）或供电子（TMS、NMe2、NH2）部分的基于螺旋烯的 pi 共轭发射体的光物理和手性光学性质的实验测量。样品在 2-MeTHF 冷冻溶液中表现出强圆偏振磷光，发光不对称因子达到 1.6 x 10-2，最活跃的分子硝基化合物的寿命超过 0.46 s。理论研究表明，虽然单重态（S1）和三重态（T1）激发态发射主要来自螺旋烯核，但自旋允许和自旋禁止发射的旋转强度具有相反的符号。对自旋轨道耦合矩阵元素的进一步分析表明，S1 和 T1 之间没有强烈混合，这证明了旋转强度的不同符号是合理的。在硝基化合物的情况下，磷光发射的增强是由于有效的系间窜越。
The experimental measurement of the photophysical and chiroptical properties of helicene-based pi-conjugated emitters with electron-accepting (-CN, -py, -NO2) or donating (TMS, NMe2, NH2) moieties is reported at low temperature (77 K). The samples exhibit strong circularly polarized phosphorescence in frozen solution of 2-MeTHF, with a luminescence dissymmetry factor reaching 1.6 x 10-2 and a lifetime of over 0.46 s for the most active molecule, the nitro compound. The theoretical investigation shows that although the singlet (S1) and triplet (T1) excited-state emissions mainly arise from the helicene core, the rotatory strengths of the spin-allowed versus spin-forbidden emission have opposite signs. Further analysis of the spin-orbit coupling matrix elements shows that there is no strong mixing between S1 and T1, justifying the different signs of the rotatory strengths. In the case of the nitro compound, the enhanced phosphorescence emission is due to an efficient intersystem crossing.