SYNTHESIS AND PHOTOPROPERTIES OF A QUENCHER, NA[CR(1,3-DIAMINOPROPANE)(CN)(4)], AND REINVESTIGATION OF CR(1,3-DIAMINOPROPANE)(3)(3+) PHOTOPRODUCT QUENCHING

The photochemical, photophysical, and general properties of the compou nd Na[Cr(tn)(CN)(4)] (tn = 1,3-diaminopropane) suggest that it has con siderable potential as a new and useful quencher. It does not absorb o ver most of the visible spectrum, and it is reasonably stable both to thermo- and photosubstitution processes. Only at a pH of 2 or less doe s acid-catalyzed loss of cyanide become significant; the first-order r ate constant at pH 2 and 20 degrees C was 4 x 10(-5) s(-1), for a half -life of 5 h. There was a quantum yield of 0.040 +/- 0.006 for photoaq uation on irradiation at 406 nm. In dmso or dmf room-temperature solut ions, the compound emits at 748 nm; in these solvents this emission ca n be used as a probe for energy transfer to the quencher. At the same time, its low charge reduces the danger of precipitation of quenching partner cations as double salts or the formation of ion pairs. The eff iciency of this quencher was explored through a comparison of its quen ching of Cr(tn)(3)(3+) with that by hydroxide; the quenching rate cons tants at 20 degrees C were (6 +/- 2) x 10(8) and 6 x 10(10) M(-1) s(-1 ), respectively. This quenching study confirmed an earlier report of d ifferent photoproduct isomer ratios for the quenched and unquenched ph otochemistry of Cr(tn)(3)(3+) but did not show the wavelength effect r eported earlier.