Transition energy tuning from 3.3 to 1.4 eV in the system $M_x\left[\mathrm{Pt}{\left(\mathrm{CN}\right)}_4\right]·m{\mathrm{H}}_2\mathrm{O}$

The electronic transition energies of the $M_x\left[{\mathrm{Pt}}^{2+}{\left(\mathrm{CN}\right)}_4\right]·m{\mathrm{H}}_2\mathrm{O}$ compounds, crystallizing in columnar structures, depend strongly on the Pt-Pt distance $R$ in the direction of the columns. $R$ can be varied by substituting $M$ and/or by application of high pressure. Using three different compounds {${\mathrm{Na}}_2$[Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$]·3${\mathrm{H}}_2$O, Ca[Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$]·5${\mathrm{H}}_2$O, Mg[Pt${\mathrm{}\left(\mathrm{CN}\right)\mathrm{}}_4$]·7${\mathrm{H}}_2$O} and applying hydrostatic pressures up to 38 kbar it is possible to adjust the emission energy continuously from 3.3 to about 1.35 eV. The pressure-induced energy shift is unusually large with values between -320 and -140${\mathrm{cm}}^{-1\mathrm{}}$/kbar.