Self-assembled binary multichromophore dendrimers with enhanced electro-optic coefficients and alignment stability

• Published in: Materials chemistry frontiers 2020-01, Vol.4 (1), p.168-175
• Main Authors: Xu, Huajun, Liu, Jianpeng, Liu, Jun, Yu, Canwen, Zhai, Zhaofen, Qin, Gangzhi, Liu, Fenggang
• Format: Article
• Language: English
• Subjects: Alignment; Chromophores; Coefficients; Crosslinking; Dendrimers; Dendritic structure; Deoxidizing; Dipole interactions; Mach-Zehnder interferometers; Modulators; Phase separation; Photonics; Refractivity; Room temperature; Self-assembly; Stability
• ISSN: 2052-1537; 2052-1537
• DOI: 10.1039/c9qm00508k

Novel binary self-assembled electro-optic (EO) dendrimers were developed to maximize the acentric order of chromophores with large hyperpolarizabilities and strong dipole-dipole interactions. To achieve high EO coefficient, a multichromophore dendritic structure and supramolecular self-assembly strategy through π-π stacking of fluoroaromatics and aromatics were adopted to minimize dipole-dipole interaction of the chromophores at high loading density. In these dendrimers, three tetraene chromophores were substituted with an aromatic dendron (HD) or a fluoroaromatic dendron (FD) on the donor ends as the peripheral groups. The neat dendrimer films show excellent film-forming ability and a higher refractive index ( n = 1.81 for FDSD and n = 1.86 for HDSD at 1310 nm) compared with guest-host EO polymers ( n 1.6, 1310 nm). Higher n is beneficial for reducing the driving voltage for Mach-Zehnder modulators. By doping a secondary chromophore (HJD, 25 wt%) into neat dendrimers and blending two dendrimers together with 1 : 1 ratio (wt), three kinds of binary EO materials were prepared to afford better EO performance and larger index of refraction without phase separation. Due to supramolecular self-assembly through FD-HD π-π interactions, the poled binary film of 1 : 1 HDSD : FDSD exhibited a very large EO coefficient value up to 289 pm V −1 together with a large refractive index ( n = 2.01) at 1310 nm, which represents a very high n 3 r 33 figure-of-merit of 2347 pm V −1 at 1310 nm. Meanwhile, a non-covalently crosslinked network was formed by the HD-FD π-π interactions which afforded an improved long-term alignment stability. After annealing at room temperature for 1000 h, about 97% of the initial r 33 values could be still maintained for the poled films of 1 : 1 HDSD : FDSD. The high poling efficiency and temporal EO stability combined with refractive index make them promising candidates for application in photonic devices. Self-assembled binary multichromophore dendrimers HDSD-FDSD have been developed to increase the poling efficiency, refractive Index and stability of the EO materials.