A characterization of graphs with rank 5

The rank of a graph G is defined to be the rank of its adjacency matrix. In this paper, we consider the following problem: what is the structure of a connected graph G with rank 5? or equivalently, what is the structure of a connected n-vertex graph G whose adjacency matrix has nullity n-5? In this paper, we completely characterize connected graphs G whose adjacency matrix has rank 5.