Hello Philip
IPv6 introduces various types of addresses including link local addresses. These are addresses that are automatically assigned to any IPv6 enabled interface. OSPF and other dynamic routing protocols, use these addresses as the source and destination of their hello packets and their exchange of routing information. For this reason, no global unicast address need be configured on any interface of a router participating in OSPF. In short, control plane traffic will use link local addresses for the exchange of control information, in this instance, OSPF messages.
Global unicast addresses on the other hand, are assigned to hosts that want to communicate on a network. These are the devices that actually send data on the network to be routed by the routers. These devices must have global unicast addresses. This is considered data plane traffic, that is, traffic sent by end devices with user data such as emails, web content, voice conversations, file transfers etc… Such traffic requires global unicast addressing, and it is the prefixes of these global unicast addresses that are being exchanged by the OSPF protocol.
So in order to be able to ping (data plane traffic) from the Gi0/1 interface of R1 to the loopback address of R2, R1 must have a global unicast address on the Gi0/1 interface.
You can find out more about link local and global unicast addresses here:
I hope this has been helpful!
Laz