I think it's Mirabilis jalapa/Four O'clock.

I'm pretty sure davidrt28 is correct after googling it. I thought it might be rattlebox, but after looking at pics of yellow baptisia online, I'm 99% sure that's it. My plants are very thin because they were completely choked by phlox and weeds which had overtaken almost the entire bed. The thinness threw me, but I imagine now what they can look like if they actually get sun.

Well, firstly, and more important than a name for them is if you want to save them they need to come out of whatever they are planted in at the moment. What is the soil you've used, it looks like ordinary garden soil maybe? They are definitely succulents and that being the case I use a free draining gritty mix made up of equal amounts of small gravel, perlite, bark chips and very gritty cactus mix (some may not advise this last ingredient as some C&S mixes are very peaty, so be careful here with what you use, if you can't get a good one, lessen the amount of it). It needs to be damp, that's all, don't water until you see signs of growth. Cut of any brown/dead/decaying end of their stem and let them dry for a day or so, it won't harm them, then plant in your new mix. A name may well come in soon, but they will not do well in that soil I'm certain. Hope this helps. Gill UK

Is this a Vinca? Blue to Purple pinwheel flowers in spring? Mojo and Illumination have variegated leaves. Here is a link that might be useful: