One interface, two signals: excited-state lifetime shortening and electrochemical enhancement in GO-rhodamine B composites

Electrochemical exfoliation of graphite rods is performed in a controlled environment to obtain graphene oxide (GO) suspensions. Graphite serves as the anode in an electrochemical cell containing H₂SO₄, NaOH and Na₂S₂O₄ electrolytes; the exfoliated material is collected, rinsed with deionised water and examined by Fourier-transform infrared spectroscopy, which confirms the oxygen functionalities characteristic of GO. GO-rhodamine B (RhB) composites at different GO:RhB mass ratios were characterised by steady-state photolumi­nescence (PL), time-resolved photoluminescence (TRPL) and cyclic voltammetry (CV). Under 520 nm excitation, where GO absorbs strongly and RhB is excited only on the short-wavelength shoulder of its S₀→S₁ band, bare GO shows strong visible PL from radiative recombination at oxygen-defect states. Progressive addition of RhB quenches this GO-centred emission and shifts the residual emission from 580 nm to 607-613 nm. TRPL shows that the emission lifetime shortens systematically with RhB loading, giving an apparent excited-state deactivation rate constant of up to 2.9×10⁸ s⁻¹ and demonstrating that the GO excited state is dynamically deactivated by RhB. The steady-state quenching exceeds the lifetime quenching, indicating an additional static (ground-state-association) component consistent with π-π adsorption of RhB on GO. CV of composite-modified electrodes shows substantially higher currents than the RhB-modified electrode; the 1:1 sample also shows a new quasi-reversible couple, with a cathodic peak at about +0.39 V (about -25 mA) and an anodic peak at about +0.72 V (about 40 mA). The separation of ΔEp ≈ 0.33 V is large for a scan at 30 mV s-1, indicating slow electron transfers typical of an adsorbed species on conducting GO. A single band-alignment framework in which GO-to-RhB excited-state transfer (photoinduced electron transfer and/or Förster energy transfer) and GO-mediated electrode coupling arise from the same interfacial π-orbital overlap is proposed and shown to be consistent with all three datasets; the electron-versus-energy-transfer distinction is identified as requiring transient absorption spectroscopy. This work addresses an under-explored regime, distinct from the predominant literature in which GO quenches RhB fluorescence under RhB-centred excitation.