a, Geometrical configuration of the donor and acceptor transition dipoles in a dimer. R is the vector joining the centers of the dipoles. b, κ2 values calculated for the dimer configurations presented in (c). c, Top: STM image (V = − 2.5 V, I = 10 pA). Scale bar 1 nm. Bottom: ball-and-stick models of the PdPc–ZnPc donor–acceptor pair with the respective dipoles indicated. d,e, Plasmon-corrected STML spectra (V = − 2.5 V, I = 300 pA, acquisition time t = 300 s) recorded at the positions marked by a black dot (d) and grey star (e) in (c). The main emission lines of each molecule are highlighted in color in the spectra. These data are also presented in Fig. 2a,d of the main manuscript.