Design,Synthesis And Properties Of Novel Double-donor Organic Second-order Nonlinear Optical Chromophores

Organic second-order nonlinear optical(NLO)material have attracted much attentions over the past two decades because of their potential advantages,such as ultrafast response,broad bandwidth,low driving voltage,tunable structures and large electro-optic coefficients(?33).These materials have potential applications in high speed EO modulators,optical sensors and telecommunications etc.The second-order NLO chromophores were the most important part of the electro-optic material.Hyperpolarizability(?)has been used to characterize the microscopic NLO activities of the chromophore.However,the challenges in preparing excellent electro-optic(EO)materials are not only to develop NLO chromophores with large ? value but also to effectively translate the microscopic ? value into macroscopic electro-optic activities.To efficiently translate the high microscopic nonlinearity of chromophore to macroscopic EO activity of materials,isolation group,shape engineering concept had emerged for the design of chromophores.In this paper,two identical electron donors(N,N-diethylaniline groups)and electron acceptors(2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile)were introduced into different active sites of ?-conjugated bridged thiophene to design and synthesize a series of novel double-donor Y-type chromophores Y0,Y1 and Y2.Thermal stability results show that all chromophores have good thermal stability.From the results of UV-vis analysis,it can be known that the introduction of two electron donors at the C2 and C5 position of thiophene and at the C2 and C3 position of thiophene can effectively increase the intramolecular charge transfer,but the introduction of two electron donors at the C2 and C4 position of thiophene significantly suppressed the ICT properties of the chromophore.From the electro-optical activity test,it can be seen that the chromophores YO(?33=25 pm V-1)which electron donors are introduced into C2 and C5 position of thiophene,electron acceptors are introduced into C3 position,and the chromophore Y1(?33=56.2 pm V-1)which electron donors are introduced into C2 and C3 position of thiophene,the electron acceptor at the C5 position.That can not only improve the microscopic nonlinearity of the chromophore,but also effectively weaken the strong dipole-dipole interaction between the chromophores,so that the organic EO material has greater macroscopic EO activity.However,the chromophore ?2(?33=5.8 pm V-1)which electron donors at the C2 and C4 position of thiophene and the electron acceptor at the C5 position could significantly weakened the macroscopic EO activity of the material.Then,a series of novel chromophores J1,JS and JO were synthesized by introducing a novel electron donor,1-oxajulonidine(J).Thermal stability results show that all chromophores have good thermal stability.The UV-vis analysis results show that the new electron donor 1-oxajulonidine has higher electron donating ability than 4-diethylaminobenzene and 4-anisole.And the introduction of auxiliary donors(thiophene and furan)can further increase the intramolecular charge transfer of chromophore molecules.And then chromophore JS(?max=662 nm,?33=15.3 pm V-1)JO(?max=669 nm,?33=13.5 pm V-1)with a new electron donor(J)has a higher EO coefficient than FTC(?max=676 nm,?33=12 pm V-1).It is indicated that introducing an electron donor with stronger electron donating ability and adjusting the conjugated bridge of the chromophore is an effective method to optimize the macroscopic EO activity of the material and improve the nonlinear/transparency contradiction.Finally,a series of novel double-donor Y-type chromophores Y3-Y8 by introducing two electron donors with different electron-donating abilitiy in C2 and C3 position of thiophene were designed and synthesized.Thermal stability results show that all chromophores have good thermal stability.UV-vis analysis showed that the chromophore that introduced a stronger electron donor into the C2 site of thiophene had stronger intramolecular charge transfer properties.And through theoretical calculations and cyclic voltammetry,it can be seen that the chromophore that introduces a stronger electron donor into the C2 site of thiophene has a smaller energy gap and a larger first-order hyperpolarizability,which indicates that the introduction The stronger electron donor and the introduction of the strong electron donor into the C2 site of thiophene make the chromophore have stronger nonlinear properties.