Effects of Dendronization on the Linear and Third-Order Nonlinear Optical Properties of Bis(thiopyrylium) Polymethine Dyes in Solution and the Solid State

Abstract

Effects of the size and attachment position of benzyl aryl ether dendrons covalently attached to bis(thiopyrylium) penta- and heptamethines on the optical properties of these dyes in solution and in solid films have been investigated. In dilute solution the low-energy absorption bands of some of the dendronized species differ from those of the parent compounds in having much smaller transition dipole moments, this effect possibly due to differences in ion pairing, while at higher concentrations, dye–dye interactions lead to a decrease in the transition dipole moments of the nondendronized species, but not of the dendronized ones. Consequently, in the high concentration range, dendronized and nondendronized species exhibit similar values of the real part of the microscopic third-order polarizability at 1550 nm. Solid-state film absorption spectra suggest that the dendrons significantly disrupt the chromophore–chromophore interactions seen for the nondendronized species, reducing, but not eliminating, linear absorption losses in the near-IR, and suppressing absorption peaks that are hypsochromically shifted from the solution spectra maximum: centrally placed dendrons have a larger effect than terminal dendronization, so that the corresponding thin-film spectra more closely resemble those seen in solution with increasing generations of dendronization. Z-scan measurements at 1550 nm indicate that the third-order susceptibility of dendronized heptamethine guest–host films depend approximately linearly on doping ratio of dyes and are in reasonable agreement with values extrapolated from solution-derived third-order polarizabilities; in contrast, the susceptibilities of films highly doped with an undendronized analogue fall short of values expected from solution polarizabilities.

High‐Optical‐Quality Blends of Anionic Polymethine Salts and Polycarbonate with Enhanced Third‐Order Non‐linearities for Silicon‐Organic Hybrid Devices

“…By employing a linear number density extrapolation to predict χ (3) values from γ values (see Table S1), it was found that these extrapolated values were in reasonable agreement with the values determined from the blended films suggesting that the chromophores can retain their polymethine‐like characteristics after being processed into high number density solid films. This is encouraging particularly given the deleterious impacts that aggregation can have on the NLO response of polymethines in the solid‐state 8. As a result, these polymethine/APC blend films exhibit large third‐order susceptibilities11 that exceed those of organic materials previously used in SOH devices3, 4 and are approximately three times larger than the value for silicon 12.…”

“…However, there are several major challenges that need to be overcome in order to effectively translate the large γ into a large χ (3) . At high molecular number densities, the intrinsic optical properties of polymethine dyes can be deleteriously affected by intermolecular interactions resulting in, for example, aggregation8 and ion‐pairing effects,9 both of which can lead to an increase in absorptive optical loss (linear and non‐linear) at AOSP wavelengths. To mitigate the potential absorptive loss from these interactions, we have employed polymer guest‐host approach to develop processable films with high chromophore number density.…”

“…Third‐order macroscopic non‐linearities of composites containing AJBC 1722‐1725 were measured at 1550 nm using the femtosecond pulsed Z ‐scan method7, 8 and the results are summarized in Table 2. First, it should be noted that third‐order molecular polarizabilities, γ , were also determined in a similar manner for these molecules in solution (see Table S1).…”

Linear and Third‐Order Nonlinear Optical Properties of Chalcogenopyrylium‐Terminated Heptamethine Dyes with Rigid, Bulky Substituents

“…Cyanine‐like thio‐ and selenopyrylium‐terminated heptamethines have shown promising optical properties in the telecommunications region of 1.3–1.6 µm including: large magnitudes of the real part of the third‐order polarizability, |Re(γ)|; fast nonlinear response (<10 −13 s); and relatively low 1PA and 2PA losses. [4b,6] However, achieving suitable optical properties for cyanine‐type dyes in high‐number density solids is often challenging: the high linear polarizabilities of these molecules favor the formation of aggregates with unfavorable 1PA and 2PA properties, and polymethine–counterion interactions can also lead to significant perturbations of the geometric and electronic structure of the dye . To limit such dye–dye and dye–counterion interactions, substitution of thiopyrylium dyes with Fréchet‐type benzyl‐aryl ether dendrons has been investigated.…”

Large Optical Nonlinearity Induced by Singlet Fission in Pentacene Films

“…[1][2][3][4][5][6][7][8][9][10][11][12] Lately,o rganic-molecule-basedn onlinear optical (NLO) materials have attracted much attention. [8][9][10][11][12][13][14][15][16] In the last decade,alarge number of chromophores with efficient NLO response have been predicted and demonstrated by manipulating the length, [8] orbital, [11] degree of twisting, [10,13] and other degrees of freedom [7,12,14] in p-conjugated molecules.T he magnitude of nonlinear susceptibility (c (3) )i s strongly dependent on the nonlinear polarization induced by incident photons,w hich can be promoted by increasing the density of excited states involving an optical transition. [6,17] So far, most studies have focused on the regime where one incident photon only excites one electron.…”