Let
$$\lambda _2$$
be the second largest eigenvalue of the adjacency matrix of a connected graph. In 2021, Liu, Chen and Stanić determined all the connected
$$\{K_{1,3}, K_5 -e\}$$
-free graphs whose second largest eigenvalue
$$\lambda _2\leqslant 1$$
. In this paper, we completely identify all the connected
$$\{K_{2,3},K_4\}$$
-minor free graphs whose second largest eigenvalue does not exceed 1. That is, we characterize all the connected outerplanar graphs satisfying
$$\lambda _2\leqslant 1$...
