diy, the smaller-leaved rhodos such as Purple Gem can take more sun than the larger-leaved ones. I know of someone who has their PG in full southern sun (in my zone), and it looks great - flowers even better. I'd wait and see how your rhodo reacts to more sun. Make sure it gets plenty of water (but not waterlogged) until it settles in. You should know next year whether or not it's going to do OK.

One more thing - I can't understand why the Purple Gems would not do well with eastern exposure. Maybe it was the soil, or the moisture conditions, and not the amount of sun?

They were definitely sun-burnt when facing east (one of them in particular). It might be because they were also against the side of our house, which is white, so the light was also reflective which probably intensified it.

Usually sunburn is a winter problem and is on old leaves. If the sunburn is on new leaves, then it may be a nutrient problem.

Wind and cold damage is indicated when the edges of the leaves become distorted and turn brown. This occurs frequently in plants that may be in a colder climate than recommended or in a location with severe exposure. Provide protection from winter winds and winter sun. Note, boron poisoning or fertilizer burn will create the same symptoms except uniformly over the plant rather than just on areas exposed to the sun and wind.

Large leaved rhododendrons are susceptible to sunscald if the plants do not receive enough moisture before the soil freezes. The leaves curl in cold winter weather, exposing the central part of the leaf but not the edges, resulting in the area near the main vein becomes desiccated and turns brown. To prevent this, water plants thoroughly before the first hard frost, protect from drying winds, apply mulch, and locate in partial shade.

Yellowing of leaves surfaces, often with brownish burned areas, occurring on leaves that are more exposed to sun, is caused by more sun exposure than the plant is able to tolerate. Some varieties need shade, while all plants that have been protected from direct sun will be tender until hardened off by gradual exposure to sun light. Possible solutions are to give the plant more shade or move it to a more protected site.

Uniformly yellowish-green leaves is often just the need for more nitrogen. This will be more noticeable in the full sun. Some less sun tolerant varieties will always be light green in full sun.

Here is a link that might be useful: How to grow rhododendrons.

Update: It's been one week since the big pine tree was removed. We have had very hot sunny weather every day since. The rhodies' spot now gets sunlight (no shade)all day, direct sunlight in the afternoon. In the past week, half of the rhodie's leaves have yellowed! Obviously, they are getting scorched and are very unhappy in this location, despite plenty of watering. Should I move them to a shady spot NOW or wait till fall? If I move them it would be their second move of the season. The long-term forecast calls for sunny days in the upper 80s for the rest of the week.

All plants that have been protected from direct sun will be tender until hardened off by gradual exposure to sun light. What you are seeing is the shock of getting full exposure when they are not conditioned to it. This year will be a mess, but future years should be OK. You get the same effect if you severely prune a rhododendron that is in sun. The leaves that were in the shade of other leaves are now fully exposed and will sun scorch easily. They should be OK next year.