Final Report Summary - LIGHT INDUCED SWITCH (Nanoporous materials and supramolecular clusters for light induced electronic switches)
The aim of the project entitled 'light induced switch' was to design and investigated the properties of new materials and supramolecular clusters which have inbuilt light initiated switches, in the form of iron(II) spin crossover (SCO) centers, for use as optical switches and storage devices, molecular sensors, chemical detectors, drug delivery, data storage, displays and other electronic devices. Along all the results, three mains results have been already published, as described here after:
- We have for instance investigated the photomagnetic properties of dinuclear material [FeII2(ddpp)2(NCS)4]*4(CH2Cl2) (ddpp = 2,5-di(2',2''-di-pyridylamino)-pyridine) (1*4(CH2Cl2)) and its partially desolvated analogue (1*1(CH2Cl2)), which undergo two- and one-step spin crossover (SCO) transitions, respectively. The chloroform clathrate 1*4(CHCl3) undergoes a relatively abrupt one-step SCO in which the two equivalent Fe(II) sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1*4(CHCl3) to form 1*3(CHCl3) and 1*(CHCl3) occurs via a single-crystal-to-single-crystal processes (monoclinic C2/c to P21/n to P21/n) in which the single Fe(II) site splits into two inequivalent sites within the dinuclear molecule of each phase. Both 1*3(CHCl3) and 1*1(CHCl3) undergo one-step spin transitions, with the former having a significantly higher SCO temperature than 1*4(CHCl3) and the latter, and each has a broader SCO transition than 1*4(CHCl3), attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials via reversibly resolvating the partially desolvated material with chloroform to produce the original one-step SCO, or with dichloromethane to produce a two-step SCO reminiscent of that seen for as-synthesized 1*4(CH2Cl2). Furthermore, we investigate the light-induced excited spin state trapping (LIESST) effect on 1*4(CH2Cl2) and 1*(CH2Cl2) and observe partial LIESST activity for the former and no LIESST activity for the latter.
- We have also investigated the consequence on light- and thermally-induced spin crossover (SCO) properties with particle size reduction from the macroscopic to microscale to nanoscale domains. Three samples with distinct particle sizes of the SCO coordination polymer [Fe(NCS)2(bpe)2] (bpe = 1,2-bis(4'-pyridyl)ethane) have been prepared via water-in-oil reverse micelle methods. Comparison of the magnetic properties with particle size reduction of these and the original macroscale slow grown crystals revealed that the spin transition becomes more gradual, more incomplete and concomitantly the transition temperature (T½) decreases - much like what is observed in metal dilution studies Importantly, here, in the first photo-induced magnetic studies on a nanoparticle SCO system, we see that even on the nanoscale photo-conversion of the low spin species to a metastable high spin state is possible. Furthermore, particle size reduction appears to have little effect on the temperature at which the stored photomagnetic information is erased. These results highlight that light-induced SCO properties are governed by direct metal coordination environment (i.e. on the molecular scale), whereas, thermal induced magnetic properties rely more on crystal packing and ligand field effects.
- Finally, we have participated to the physical study of new molecular clusters. Along that we have offered a straight-forward strategy for the in-situ ligand synthesis of a novel cyanide-bridged cyclo-metallomacrocycle [Fe4(CN)4L4](CN)2(SeCN)2 which has been structurally characterised by X-ray crystallography. Magnetic measurements indicate the presence of both high and low spin Fe(II) centres, while the electrochemical data are consistent with weak electronic coupling between the adjacent metal ions. Further studies are underway to elaborate the metal ions that are amenable to this synthetic strategy.
- We have for instance investigated the photomagnetic properties of dinuclear material [FeII2(ddpp)2(NCS)4]*4(CH2Cl2) (ddpp = 2,5-di(2',2''-di-pyridylamino)-pyridine) (1*4(CH2Cl2)) and its partially desolvated analogue (1*1(CH2Cl2)), which undergo two- and one-step spin crossover (SCO) transitions, respectively. The chloroform clathrate 1*4(CHCl3) undergoes a relatively abrupt one-step SCO in which the two equivalent Fe(II) sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1*4(CHCl3) to form 1*3(CHCl3) and 1*(CHCl3) occurs via a single-crystal-to-single-crystal processes (monoclinic C2/c to P21/n to P21/n) in which the single Fe(II) site splits into two inequivalent sites within the dinuclear molecule of each phase. Both 1*3(CHCl3) and 1*1(CHCl3) undergo one-step spin transitions, with the former having a significantly higher SCO temperature than 1*4(CHCl3) and the latter, and each has a broader SCO transition than 1*4(CHCl3), attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials via reversibly resolvating the partially desolvated material with chloroform to produce the original one-step SCO, or with dichloromethane to produce a two-step SCO reminiscent of that seen for as-synthesized 1*4(CH2Cl2). Furthermore, we investigate the light-induced excited spin state trapping (LIESST) effect on 1*4(CH2Cl2) and 1*(CH2Cl2) and observe partial LIESST activity for the former and no LIESST activity for the latter.
- We have also investigated the consequence on light- and thermally-induced spin crossover (SCO) properties with particle size reduction from the macroscopic to microscale to nanoscale domains. Three samples with distinct particle sizes of the SCO coordination polymer [Fe(NCS)2(bpe)2] (bpe = 1,2-bis(4'-pyridyl)ethane) have been prepared via water-in-oil reverse micelle methods. Comparison of the magnetic properties with particle size reduction of these and the original macroscale slow grown crystals revealed that the spin transition becomes more gradual, more incomplete and concomitantly the transition temperature (T½) decreases - much like what is observed in metal dilution studies Importantly, here, in the first photo-induced magnetic studies on a nanoparticle SCO system, we see that even on the nanoscale photo-conversion of the low spin species to a metastable high spin state is possible. Furthermore, particle size reduction appears to have little effect on the temperature at which the stored photomagnetic information is erased. These results highlight that light-induced SCO properties are governed by direct metal coordination environment (i.e. on the molecular scale), whereas, thermal induced magnetic properties rely more on crystal packing and ligand field effects.
- Finally, we have participated to the physical study of new molecular clusters. Along that we have offered a straight-forward strategy for the in-situ ligand synthesis of a novel cyanide-bridged cyclo-metallomacrocycle [Fe4(CN)4L4](CN)2(SeCN)2 which has been structurally characterised by X-ray crystallography. Magnetic measurements indicate the presence of both high and low spin Fe(II) centres, while the electrochemical data are consistent with weak electronic coupling between the adjacent metal ions. Further studies are underway to elaborate the metal ions that are amenable to this synthetic strategy.