Molecular solids whose cooperative electronic properties are based purely on pi-electrons from carbon atoms offer a fertile ground in the search for exotic states of matter, including unconventional superconductivity and quantum magnetism. The binary caesium salt of phenanthrene, Cs(C14H10) is a Heisenberg antiferromagnet with a candidate gapped spin-liquid state emerging from the highly-frustrated Delta-chain magnetic topology of coupled alternating-exchange spiral tubes of S=½ (C14H10)•- radical anions. The absence of long-range magnetic order down to 1.8 K (T/J~0.02) renders the compound an excellent candidate of a spin-½ quantum spin liquid arising purely from carbon pi-electrons. With this proposal we want to address the nature of the magnetic state down to mK temperatures using the ZF/LF muSR techniqueand search for the emergence or not of long-range antiferromagnetic order.