Abstract
Four knot-isomers of Mobius cyclacene are composed of 15 nitrogen-substituted benzo rings. They are non-Mobius cyclacenes without a knot (0), Mobius cyclacenes with a knot (1), non-Mobius cyclacenes with two knots (2), and Mobius cyclacenes with three knots (3). Their structures and nonlinear optical properties are systematically studied. The order of first hyperpolarizability (beta(0)) is 4693 (0) < 10 484 (2) < 25 419 (3) < 60 846 au (1). The beta(0) values of the knot-isomers with knot(s) are larger than that of the knot-isomer without a knot. It shows that the beta(0) value can be dramatically increased (13 times) by twisting the knot(s) to the cyclacene, Two noticeable relationships between the number of knots and the first hyperpolarizability have been observed: (i) the beta(0) values of one surface Mobius cyclacene (1 and 3) with an odd number of knots are larger than that of two-surface non-Mobius cyclacenes (0 and 2) with an even number of knots. (ii) For the one-surface Mobius cyclacenes, the beta(0) value for 1 with one knot is larger than that for 3 with three knots. On the other hand, the largest component of beta(0) is alternated for the four knot-isomers, The largest components are beta(z) for the 0 and beta(y) for the 1 and 2. The largest component turns back to the beta(z) for the 3.