Schematic representation of the polarization resolved HRS measurement. The incident beam is propagating along the Z axis and is polarized along the X axis. The SH-scattered light is measured along the Y axis with the polarization along the X and the Z axes.
Tropylium cation and π donors chosen for this study.
Normalized second harmonic intensity, I2ω/Iω 2 as a function of concentration of the TRO-MES complex.
The centre of mass of the cationic complex consisting of the substituted benzene (R is either CH3 or H) donor and the tropylium acceptor pair at the origin of the reference frame. The centre of mass of the BF4 − counterion is placed at a distance of 6.5 Å along the x axis. The angle θ describes the rotation of BF4 − about the z axis whereas ϕ describes the same about the y axis.
Trigonal arrangement in solution with 3 C-BF4 − moieties that is used for calculating the NLO coefficients of the cation-π complex. C stands for the complex between tropylium cation and the substituted methyl benzene.
Experimental β HRS values, wavelength of maximum absorption (λ max), and molar extinction coefficient (ɛ) at λ max for the cation-π complexes in acetonitrile.a
Measured linear and circular depolarization ratios for the cation-π complexes in acetonitrile.
Selected structural parameters of the CT complexes in their ground state optimized geometries. The distances are between an atom in the donor molecule and an atom in the acceptor molecule in the MP2/6-31g* (CP) optimized geometry. The last column gives the angle between the molecular planes of the donor and the acceptor moieties.
Vertical singlet excitation energies (in some cases lowest two energies) of all the CT complexes and their oscillator strengths (in parenthesis) are shown. Calculated tumbling averaged first hyperpolarizability ||β|| and the linear and circular depolarization ratios are also given in the table.
Calculated linear and nonlinear optical properties of the three cation-π-BF4 − complexes, arranged in a C3 symmetric fashion (Fig. 5). The oscillator strengths corresponding to excitation energies are given in parentheses next to the gaps. All the calculations are performed in acetonitrile using the SCRF model within a correction vector (CV) approach. D and D′ are the linear and circular depolarization ratios, respectively. Angles θ and ϕ are defined in Fig. 4.
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