Photorefractive Performance of Hyperstructured Cyclotriphosphazene Molecular Glasses containing Carbazole Moieties

Abstract

Two hyperstructured photorefractive (PR) molecular glasses (M1 and M2) with a cyclotriphosphazene core are synthesized via nucleophilic substitution and an azo‐coupling reaction. These molecules exhibit excellent solubility in common organic solvents and maintain a complete amorphous state in spite of their high glass‐transition temperature. The nonlinear optical effects, two‐beam coupling and four‐wave mixing, respectively, are used to prove the PR performance in the optically transparent films of M1 and M2 doped with 30 % N‐ethyl‐carbazole. With no external electric field, a gain coefficient of 102 cm–1 and diffraction efficiency of 24 % are obtained in the composite made from M1, and an even higher gain coefficient of 214 cm–1 and diffraction efficiency of 31 % are obtained in the composite made from M2 owing to its higher chromophore loading.

Photorefractive hyper-structured molecular glasses constructed by calix[4]resorcinarene core and carbazole-based methine nonlinear optical chromophore

“…Compared with the cyclotriphosphazene-based HSMGs with D.I. values of 16.7% or 33.3%, [10] the NLO 5) did indicate that the Cz-CSN contents of resultant HSGMs increased with the fed Cz-CSN-OH increase, which will be discussed later. As non-crystalline materials are required for achieving good performance for PR devices, and low molecular organic compounds are easily to crystallize in solid state, a major challenge in developing molecular glass PR materials is how to make the low molecular weight organics form a stable amorphous phase at room temperature.…”

“…In the TBC experiment, the initial power of two writing beams (beam 1 and beam 2) was 8 and 16 mW, respectively. The TBC coupling gain coefficient (Γ, cm -1 ) was estimated by the following expression [10,44] :…”

“…[7,8] However, with the increasing of NLO chromophore doping concentration, the unfavorable antiparallel packing of chromophores resulting from the strong interchromophore dipole-dipole interactions gradually appeared, leading to a decreased PR effect. [9] Recently, some nonlinear molecules such as hyper-structured molecules (HSMs), [10] star-shaped molecules, [11] dendritic molecules, [12] etc. with three-dimensional (3D) branched structure for reducing the detrimental dipole-dipole interactions, have been designed and synthesized for trying to solve this problem.…”

“…[14] Previously in our lab, using cyclotriphosphazene as the core, carbazole as CT units, and carbazole-azo-nitrobenzene as NLO chromophores, two PR HSMGs (Chart S2, ESI †) were synthesized by post-functionalization method, and the synthesized HSMG showed good PR performance. [10] As the small size of cyclotriphosphazene core has high steric hindrance, only one or two NLO chromophores were incorporated into the core. In theory, the NLO effect is proportional to the effective chromophore concentration.…”

Organic Photorefractive Materials and Applications

“…A similar approach to organic glasses is the utilization of covalently bond structures of a monomeric hole-conductor moiety and chromophore as building block for LMW-organic glasses. Examples include ECYENPA ( 71 ), [ 157 ] DRDCTA ( 70 ) [ 193 ] and Cz-C6-DCST ( 72 ), [ 194 ] a hyperstructured cyclotriphosphazene molecular glass, [ 195 ] amongst others. High gain coeffi cients of Γ = 415 cm − 1 were achieved in a glassy material made of a mixture of two DCDHF ( 69 )-based glasses sensitized by 1 wt.% TNFM at 830 nm NIR illumination, [ 192 ] which is clearly due to the benefi t of high chromophore content provided by the glass approach.…”