Synthesis and spectral characterization of photoswitchable oligo(p-phenylenevinylene)–spiropyran dyad

Abstract

In view of designing a new class of photoswitchable fluorescence probes and operating them in solution as well as on solid substrates, we have envisioned the possibility of attaching photochromic spiropyran (SP) to the highly efficient fluorophore oligo(p-phenylenevinylene) (OPV). A new dyad, SP–OPV–SP (10), was synthesized and characterised both in solution as well as in a film on a solid substrate, where two SP units as photochromic acceptors are attached to the two ends of OPV, a fluorescent donor. External stimulations (ultraviolet light, visible light and acid) generate reversible changes in the structure, resulting in changes in the absorption spectrum and fluorescence emission spectrum of dyad 10 due to the presence of the two spiropyran units. Photoinduced (ultraviolet light) isomerization of the spiropyran causes a 60% decrease in the emission intensity of OPV in the photostationary state in a solution of 60 μM concentration. In the solid state, ultraviolet irradiation causes a ∼98% reduction in the fluorescence intensity of OPV. The photogenerated isomer is somewhat more stable in solid state than in solution. The fluorescence intensity of dyad 10 is modulated by reversible conversion among the three states of the photochromic spiropyran units and the fluorescence resonance energy transfer (FRET) between the MC form of SP and the OPV unit. In any case, these investigations demonstrate that the design of dyad 10 is viable for the realization of photoswitchable molecular assemblies and can evolve as efficient fluorescent probes for potential applications in molecular device design, such as an integrated logic gate with multiple inputs and a single output.