The Design of an Optical Switch Based on Dinuclear Ruthenium Pentaammine Dicyanamide Complexes

A novel photochromic polymer (SP-PS) with a polystyrene (PS) backbone linked to spiropyran (SP) by alkyl chain was synthesized (4% yield). Ultraviolet irradiation of SP-PS induces photoisomerization from SP to merocyanin (MC); back-reaction occurs thermally or by visible irradiation. SP-PS was characterized by 1H-NMR spectroscopy, differential scanning calorimetry and gel permeation chromatography. The Tg and Mn were determined to be 118.41 °C and 63,980 g/mol ± 1.731% (Đ=1.24), respectively. Φ365 nm for SP-MC photoisomerization was 0.80 after 5 s (toluene). When SP-PS is combined with [{Ru(NH3)5}2(μ-dicyd)][BPh4]4, (dicyd2- = dicyanamido benzene dianion), a near-infrared photoswitchable material results. Interaction between MC and [{Ru(NH3)5}2(μ-dicyd)][BPh4]4 was observed through comparison of MC-SP photoisomerization rates. Thin films of [{Ru(NH3)5}2(μ-dicyd)][BPh4]4 in polystyrene displayed unique photochemistry; 30 s of 523 nm irradiation by light-emitting diode reduced ligand-to-metal charge transfer band absorbance by 70% with 82% recovery after 46h. The mechanism of this effect remains to be determined.