Usually, Schiff Bases synthesis is perfect for a pair of good nucleophiles (amine group attached to a methylene chain) and a good electrophile (aromatic aldehydes). In your case, the 2-amino benzothiazole is a weak nucleophile and therefore the reaction is more likely with a good electrophile. I suggest you 3,5 or 3- substituted aromatic aldehydes such as 3-hydroxysalicylaldehyde or 3,5-dihalosalicylaldehyde. As a solvent, you should try either ethanol or DMF. Moreover, you can use catalytic amounts of p-toluenesulphonic acid.