Influence of polar solvents on growth of potentially NLO active organic single crystals of N-benzyl-2-methyl-4-nitroaniline and their efficiency in terahertz generation

We report on the growth of N-benzyl-2-methyl-4-nitroaniline (BNA) crystals by a solution growth method using certain polar protic and aprotic solvents (single or mixed). It was observed that the morphology of the BNA crystals could be influenced by the solvents used and that the growth was, with certain exceptions, predominant along the crystallographic b axis. Attempts to grow large BNA crystals from these solvents showed that the majority of these polar solvent molecules tended to get adsorbed preferentially along the polar +c and/or -c axes/axis. The bulk and surface qualities of the grown crystals were observed to be influenced by the solvents employed to grow the BNA crystals and the results of THz measurements obtained for the crystals grown from selected solvents were also found to corroborate these observations. A systematic approach has shown that the BNA crystals grown from one of the polar aprotic solvents, which is presumably reported for the first time for this crystal, exhibited a relatively higher THz efficiency. It is further understood that this particular solvent created a favorable solute-solvent environment at the progressing crystal-solution interface which improved the overall quality of the BNA single crystals and resulted in the significant enhancement in the THz efficiencies.