Linear and Nonlinear Optical Properties of a Macrocyclic Trichromophore Bundle with Parallel-Aligned Dipole Moments

Abstract

A macrocyclic trichromophore bundle 1 with parallel-aligned dipole moments has been synthesized to study the influence of aggregation and orientation of a nonlinear optical (NLO) chromophore on its optical properties. The linear and nonlinear optical properties of 1 and a single chromophore standard 2 have been studied by UV-vis absorption, fluorescence, solvatochromic spectrometry, and hyper-Rayleigh scattering (HRS). Reduced first-order hyperpolarizability beta, hypsochromic shift, enhanced solvatochromic shifts, and fluorescence quenching for individual chromophores were observed when 1 was compared with 2. Analysis of the data showed that the transition dipole moment changes only slightly when the chromophores are parallel aligned in the bundle architecture. However, the apparent hyperpolarizability of the individual chromophores decreased significantly by about 20%. The reduction in beta for the individual chromophores in 1 is largely due to the hypsochromic shift, i.e., excitation energy increase of the interband (charge-transfer) energy gap and the reduced difference between the ground-state and excited-state dipole moments. The hypsochromic shift and fluorescence quenching are consistent with exciton theory. Possible reasons for the enhanced solvatochromic shift are discussed.

Two-photon resonant hyperpolarizability of an H-shaped molecule studied by wavelength-tunable hyper-Rayleigh scattering

“…35 Considering the second-order optical properties, there is a significant increase in β value per chromophore for S2 relative to S1. 49 In these two cases the distances between the D-π -A units in a molecule were much larger than that of S2 in this work. Kelley calculated both Hand J-dimer's hyperpolarizabilities with enhanced and reduced values relative to that of the monomer, respectively.…”

2,2′‐Bipyridine‐Based Dendritic Structured Compounds for Second Harmonic Generation

“…Therefore, two principal synthetic alternatives are possible: one introduces a covalently bound cap (Figure 1, left), and another implements coordination sites within a dendron providing a conformational rigidity upon coordination of a metal ion (Figure 1, right). Both ways have turned out to be preparative challenges 6,10. In this study we describe the introduction of 2,2′‐bipyridine (bpy) as coordination sites into the dipolar branches, which are prone to form helical structures upon coordination,11 and we characterize the linear and nonlinear optical properties of a dipolar single strand and the corresponding triple‐stranded dendritic structure.…”

“…Both ways have turned out to be preparative challenges. [6,10] In this study we describe the introduction of 2,2'-bipyridine (bpy) as coordination sites into the dipolar branches, which are prone to form helical structures upon coordination, [11] and we characterize the linear and nonlinear optical properties of a dipolar single strand and the corresponding triple-stranded dendritic structure. This is done by experimental measurements and time-dependent density functional theory (TDDFT) calculations using different functionals under consideration of solvent effects by applying two solvation models.…”

Unexpected High Second‐Order Nonlinear Optical Activity of Metal Complexes with Three‐Branched Hexadentate 2,2′‐Bipyridine Ligands

“…A helical and close alignment of electron‐donor–electron‐acceptor entities with a large π‐conjugated backbone is of particular interest, since they can provide interchromophore dipolar interaction resulting in cooperative effects, provoking an increase in the NLO properties …”