We designed and synthesized a series of new electro-optic quinolinium crystals with modifying sulfonated anions for THz applications. Compared previously reported HMQ-T (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 4-methylbenzenesulfonate) crystals exhibiting about 3 times higher THz generation efficiency than benchmark polyene crystals, newly designed HMQ-TMS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium 2,4,6-trimethylbenzenesulfonate) crystals possess completely optimal molecular packing for electro-optic applications and exhibit 20% larger nonlinear optical responses. By enhancing solubility with 3.4 times higher than HMQ-T crystals, bulk HMQ-TMS crystals with a size of up to 18 ？e 15 ？e 8 mm3 are easily grown by slow cooling method. While thin thickness with small size of HMQ-T crystals limited the beam path-length and aperture size, respectively for THz wave generation, thick thickness with large size of HMQ-TMS crystals allowed longer beam path-length and larger aperture size. We have demonstrated THz generation with HMQ-TMS crystals by optical rectification using 200 fs pulses at pump wavelength of 836 nm.
