Make sure the ethanol you are using is anhydrous and keep things covered with aluminum foil or watch glass to avoid water. Try adding enough hot ethanol (might take quite a bit) to fully dissolve the resinous material, and allow the solution to cool to room temp. If no crystals form, then slowly add anhydrous diethyl ether until the solution just turns cloudy, cover the cloudy solution and let it stand overnight. You could refrigerate this solution overnight in an explosion proof refrigerator if you have one available. Alternatively you might need water of hydration to get crystals to form so if the above method does not work try the same thing using 95% ethanol.  

Thanks!  The next step is reacting with sodium borohydride to reduce the imines.  Do you think recrystallization is absolutely necessary before proceeding with the sodium borohydride?  I'm hoping that adding the terephthalaldehyde very slowly in the first step gave me mostly the cyclic product.  Do this think this is a safe assumption?

Imines can be unstable but the corresponding amines much more stable so reducing them with NaBH4 might be the way to go. The problem is you already know the imine you want is a solid which has the potential to be crystallized. The amines may not be as easy to get to crystalline especially as a free base, you may have to form a salt to get crystals. Some amine salts namely the hydrochlorides are notorious for being hygroscopic and are not easily handled. 

If you have an abundance of cheap starting materials I suggest you try reducing the imine to the amine and seeing if you can come up with a clean enough material for further research work. Taking this step even on a small scale should give you the authentic amine you can use as a reference material for later reactions.

Adding the terephthaldehyde slowly to the diethylenetriamine solution is a great idea as it should favor the disubstitution of the terephthaldehyde; but only dilution will favor cyclization over polymerization. I have used a syringe pump and an all plastic syringe with a long stainless steel needle to add things slowly to a reaction; the syringe pump allows for precise control of the time it takes for the addition.

I skipped recrystallization and went right to the NaBH4, then extraction with dichloromethane.  Then drying,  then salt formation with HBr in Methanol.  Got a nice white powder.   Last time I got to this step the NMR looked good,  but I was scared by the tendency of the first product to turn sticky when heated in ethanol.   This time I avoided hearing it and hoped the purity wouldn't suffer by not recrystallizing.  I think I can use column chromatography for purification, or just go for elemental analysis as is and see what I have. 

Be careful with the elemental (and NMR) analysis results, a higher order cyclic structure or polymer might look like the cyclic product you are trying to isolate in both techniques. I suggest you get a mass spectrum, even a low resolution one, to at least confirm you have isolated a compound with the correct molecular weight. If this is indeed an HBr salt you should also be able to see the Br- ion in the negative ion mode.

Thanks!   Nearly all my research has been cell biology, instrumental analysis,  and animal work,  so this is quite an undertaking.   I think I'm going to use Stanford's analytical service at this point to see what I have.   They have a structure elucidation service and of course mass spec.   My small University has some of the necessary equipment,  but it seems no one is available to run the samples or orient me to the instruments.   I've used electrospray before, but this new instrument in the chem Department is not something I want to touch without training.  If you were interested in collaborating that'd be great.   I'm actually trying to further refine the fluorescein quencher that's been published before.   Today I reacted with copper nitrate to form the chelate,  hoping I had the right starting material.   I'm going to test it's quenching ability tomorrow,  and then go from there.   The big problem I'm seeing is that the structure without copper is supposed to be soluble in methanol,  but I'm finding that I can only get it to dissolve in water, and no other solvents at all. 

Before you spend a lot of time and money, I suggest using a cheap and simple analytical technique like TLC.  Try to develop a solvent system that differentiates between the starting materials and product(s) and at least confirm the starting materials are no longer present. Reduce some of the terephthaldehyde with NaBH4 and confirm that this compound is also absent. I suggest running a silica gel TLC plate in methanol with 0.1% formic acid and developing the plate with iodine fumes as the first try. If there are TLC conditions reported in the literature then use those conditions. You might find that your preparation is not as pure as you thought it was, besides TLC provides a useful starting point for column chromatography purification (like Flash chromatography). If TLC isn't readily available, investigate the compounds purity by using an alternative method like HPLC. Keep in mind you precipitated out a powder which may not have purified anything like an actual recrystallization would.

I definitely have access to TLC in the lab.  I'll do exactly what you mention, and report back here.   I'll have a few students working on this throughout the summer,  and I wanted to make some headway first so we have at least something to start with. 

Regarding the starting materials: both of them are soluble in acetonitrile, and that is what they are both dissolved in when I add the solution of terephthalaldehyde slowly to the DETA.  I can immediately see a precipitate forming when the drops mix with the DETA solution.  After overnight mixing there's a lot of yellowish/white precipitate, and that should be the correct product.  I'm confident that it isn't the starting material because it is insoluble.  I then wash with more acetonitrile and ether, before adding sodium borohydride for reduction of the double bonds.  I'm not sure why I need to make the salt, and in fact, I'm starting to think the salt is only being made in the one article as that is the finished product.  However, I need to use the product for the addition of copper, so I'm thinking the salt is a futile step in my case, but I'm not sure.  I also have no idea if using the salt has any bearing on the reaction of copper.  I know this much, the salt isn't soluble in anything but water, and I'm supposed to be reacting the copper with the product in methanol.  That is a sign that using the salt is not helping me.  Would you say I'm correct in assuming the starting materials should be gone after the wash step?

All the free starting materials should be removed by the wash step. However the terephthaldehyde may bind to the secondary amine of DETA forming a less stable imine, and the wash step may not remove these adducts from the product but they can be removed by crystallization. What salt of copper are you adding?

I'm using copper (II) nitrate