Optimizing the molecular structure of 1,1,7,7-tetramethyl julolidine fused furan based chromophores by introducing a heterocycle ring to achieve high electro-optic activity

Abstract

Developing new organic chromophores with a large electro-optic coefficient (r₃₃) is highly desirable for fabricating electro-optic (EO) materials. Building on the fact that the 1,1,7,7-tetramethyl julolidine fused furan ring is a good electron donor and lengthening the π-bridge of a chromophore with a five-membered heterocycle ring could lead to the improvement of r₃₃. Here we design and synthesize two new chromophores C1 and C2 by using a 1,1,7,7-tetramethyl julolidine fused furan ring as the electron donor and 2-(3-cyano-4,5,5-trimethyl-5H-furan-2-ylidene)-malonitrile (TCF) as the acceptor, but with two different π-bridges (furan-vinylene and thiophene-vinylene accordingly). When doping C1 or C2 into PMMA with a loading density of 20 wt%, the poled films containing C1 or C2 exhibited an r₃₃ value of 75 pm V⁻¹ and 94 pm V⁻¹, respectively. When compared with chromophore C3 (an ene unit as the π-bridge, r₃₃ = 52 pm V⁻¹), an enhanced r₃₃ of C1 and C2 was achieved due to the introduction of a heterocycle ring into the π-bridge. This work uncovers the influence of the heterocycle ring on the julolidine fused furan based chromophore's physical and chemical properties and demonstrates that the new chromophores are a promising candidate for EO material application.