Highly Efficient Organic THz Generator Pumped at Near‐Infrared: Quinolinium Single Crystals

Abstract

A novel highly efficient ionic electro‐optic quinolinium single crystals for THz wave applications is reported. Acentric quinolinium derivatives, HMQ‐T (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methylbenzenesulfonate) and HMQ‐MBS (2‐(4‐hydroxy‐3‐methoxystyryl)‐1‐methylquinolinium 4‐methoxybenzenesulfonate) exhibit high order parameters cos3θp = 0.92 and cos3θp = 1.0, respectively, as well as a large macroscopic optical nonlinearity, which is in the range of the benchmark stilbazolium DAST (N,N‐dimethylamino‐N’‐methylstilbazolium 4‐methylbenzenesulfonate) and phenolic polyene OH1 (2‐(3‐(4‐hydroxystyryl)‐5,5‐dimethylcyclohex‐2‐enylidene)malononitrile) crystals. As‐grown unpolished bulk HMQ‐T crystals with a side length of about 6 mm and thickness of 0.56 mm exhibit 3.1 times higher THz generation efficiency than 0.37 mm thick OH1 crystals and about 8.4 times higher than 1 mm thick inorganic standard ZnTe crystals at the near‐infrared fundamental wavelength of 836 nm. Therefore, HMQ crystals with high order parameter obviously have a very high potential for high power THz‐wave generation and its applications.

N-Methylquinolinium derivatives for photonic applications: Enhancement of electron-withdrawing character beyond that of the widely-used N-methylpyridinium

“…2a) were synthesized by a condensation of 4-(dimethylamino)benzaldehyde with the corresponding dimethylquinolinium 4-methylbenzenesulfonate (DMQ-T) intermediates in a similar manner as reported previously [33]. For comparison, the pyridinium-based DAST chromophore was synthesized by a condensation of 4-(dimethylamino)benzaldehyde with 1,4-dimethylpyridinium 4-methylbenzenesulfonate (DMP-T) in a similar manner as reported previously [27].…”

“…A mixture of 2-methylquinoline (50 mL, 0.351 mol) and methyl 4-methylbenzenesulfonate (54 mL, 0.351 mol) in 1,2-dimethoxyethane (300 mL) was stirred at 50 C. After stirring for 6 days, the precipitated powder was filtered and then dried in vacuum oven at 100 C for overnight [33]. …”

Organic styryl quinolinium crystal with aromatic anion bearing electron-rich vinyl group

“…HMQ (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium) cation forms strong Coulombic interactions with benzenesulfonate anions. In the previously reported HMQ-T (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate) crystal [17], the counter anion is 4-methylbenzenesulfonate. In HMQ-T crystals, the methyl group on 4-methylbenzenesulfonate plays a significant role in the formation of the anion layer in the crystalline state, as the hydrogen atom of the methyl group and the oxygen atom of the sulfonate group forms the second strongest hydrogen bond (eCeH/ À OSe) in the anion layer [17,32].…”

“…In the previously reported HMQ-T (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate) crystal [17], the counter anion is 4-methylbenzenesulfonate. In HMQ-T crystals, the methyl group on 4-methylbenzenesulfonate plays a significant role in the formation of the anion layer in the crystalline state, as the hydrogen atom of the methyl group and the oxygen atom of the sulfonate group forms the second strongest hydrogen bond (eCeH/ À OSe) in the anion layer [17,32]. Here, instead of having an aliphatic methyl group on the benzenesulfonate counter anion, a relatively large, electron-rich p-conjugated vinyl group was introduced to obtain HMQ-VBS, synthesized by a methathesization reaction between 2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium iodide and sodium 4-vinylbenzenesulfonate.…”

“…The crystal characteristics and physical properties of the HMQ-VBS crystals were investigated. For comparison, the previously reported analogous HMQ crystal with 4-methylbenzenesulfonate (HMQ-T) [17] were also characterized. HMQ-VBS and HMQ-T crystals have roughly similar features in terms of their molecular alignment, resulting in identical physical properties in the solution state but are significantly different in the crystalline state.…”