Crystal Structures, Degree of Charge Transfer, and Non-Linear Optical Characteristics of Intramolecular Charge-Transfer Compounds: Indoline-Substituted Tricyanoquinodimethanes

摘要

The substituent effect on the degree of intramolecular charge transfer (delta) and optical properties of donor-pi-acceptor compounds comprised of 1,3,3-trimethyl-2-methyleneindoline (I-t) and substituted 7,8,8 -tricyanoquinodimethane (=2-(4-cyanomethylene-2,5-cyclohexadienylidene)inalononitrile, 3CNQ-R, R = substituent groups) moieties were investigated (I-1-3CNQ-R). In the crystal structures, I-1-3CNQ-R molecules stacked on indoline and/or 3CNQ-R moieties in a head-to-tail manner to cancel their dipole moments and established segregated or mixed stack columnar motifs. The 3 values of I-1-3CNQ-R molecules in solid and solution states were estimated using the bond length ratio in the crystal structures, molecular orbital calculation, and the solvatochromic shift of intramolecular charge-transfer absorption, respectively, and showed significant and reasonable dependences on substituents of the 3CNQ moiety. Structural analysis revealed that molecular conformation and planarity affect the 8 values of I-1-3CNQ-R molecules. Molecular orbital calculations revealed that molecular (hyper)polarizabilities can be modulated by tuning delta. I-1-3CNQ-R exhibited a solvatochromic shift, and the ground state changed from neutral (delta <= 0.5) in less-polar solvents to ionic (delta >= 0.5) in polar solvents. Two-photon absorption properties of I1-3CNQ-R showed a significant substituent effect and indicated that delta is a fundamental parameter for modulating non-linear optical properties.