Encapsulation of P-carotene inside single-waited carbon nanotubes (SWCNTs) greatly improves the stability of P-carotene. The Figure shows a schematic illustration of beta-carotene inside a SWCNT. The surrounding tube wall protects P-carotene from reacting with radical species and suppresses its isomerization. This protection counters the degradation of pi-conjugated molecules, which is a bottleneck impeding their application in photonic devices.