Fig. 1: Set-up, triplet decay under resonant driving and ESR-AFM spectra.

a, Sketch of the experimental set-up. Individual pentacene molecules were adsorbed on a Au(111) microstrip on a mica disc, covered by a NaCl film (>20 monolayers), preventing electron tunnelling between microstrip and molecule. A time-dependent gate voltage V_G was applied to the strip to repeatedly bring the molecule in the neutral triplet excited state T₁ (represented by the two arrows) by two subsequent tunnelling events between molecule and conductive tip. During an experimentally controlled dwell time t_D, the neutral molecule can decay to the singlet ground state. An RF current I_RF was run through the microstrip to generate an RF magnetic field. After t_D, the final state of the molecule was read out as described in Methods. b, Decay of the T₁ state as measured without RF (red) and with a broadband (see Methods) RF pulse (black). T₁ is zero-field-split into three states T_X, T_Y and T_Z having different lifetimes (inset), such that the RF pulse driving the T_X–T_Z transition changes the resulting overall decay. Solid lines represent fits to triple-exponential decays. Each data point corresponds to 1,920 pump–probe cycles and the error bars were derived from the s.d.; see ref. ¹⁵. c,d, ESR-AFM spectra of the T_X–T_Z and T_X–T_Y transitions of a pentacene-h₁₄, respectively. The RF was swept at a constant t_D = 100.2 μs. The AFM signal Δf was normalized to Δf_norm as described in Methods. It can be calibrated against the triplet population¹⁵ at t_D; see right axes. The error bars were derived from the s.d. of seven and 38 measurements, respectively.