A series of stiff stilbene macrocycles have been studied to investigate the possible impact of the macrocycle ring size on their photodynamic properties. The results show that reducing the ring size counteracts the photoisomerization ability of the macrocycles. However, even the smallest macrocycle studied (stiff stilbene subunits linked by a six carbon chain) showed some degree of isomerization when irradiated. DFT calculations of the energy differences between the E- and Z-isomers show the same trend as the experimental results. Interestingly the DFT study highlights that the energy difference between the E- and Z-isomers of even the largest macrocycle (linked by a twelve carbon chain) is significantly higher than that of the stiff stilbene unit itself. In general, it is indicated that addition of even a flexible chain to the stiff stilbene unit may significantly affect its photochemical properties and increase the photostability of the resulting macrocycle.

中文翻译：

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环丁烯对硬苯乙烯二环大环化合物光致异构化性能的影响

已研究了一系列刚性二苯乙烯大环化合物，以研究大环环尺寸对其光动力性质的可能影响。结果表明，减小环的尺寸抵消了大环的光异构化能力。但是，即使是研究的最小的大环化合物（通过6个碳链连接的刚性二苯乙烯亚基）在辐照时也表现出一定程度的异构化。E和Z异构体之间的能量差的DFT计算显示出与实验结果相同的趋势。有趣的是，DFT研究强调了E-和Z之间的能量差即使是最大的大环（由十二个碳链连接）的α-异构体也比刚性二苯乙烯单元本身的α-异构体高得多。通常，表明即使向刚性二苯乙烯单元添加挠性链也可显着影响其光化学性质并增加所得大环化合物的光稳定性。