Phosphorus–Nitrogen\nCompounds: Part 76. Design\nand Syntheses of Dispiro- and Trispiro(N/N)cyclotriphosphazenes: Conformational\nand Structural Analyses, Chirality, Electrochemical, Dye-Sensitized\nSolar Cells, and Bioactivity Studies

The reactions of monospirocyclotriphosphazenes (<b>1</b> and <b>2</b>) with <i>N</i>-methyl-1,3-diaminopropane\ngave\nunsymmetrical <b>cis</b>-(<b>3</b> and <b>5</b>)\nand <b>trans</b>-(<b>4</b> and <b>6</b>) dispirocyclotriphosphazenes.\nTrans–cis–trans (<b>tct</b>) (<b>7</b> and <b>11</b>), cis–cis–cis (<b>ccc</b>) (<b>8</b> and <b>12</b>), trans–trans–cis (<b>ttc</b>) (<b>9</b> and <b>13</b>), and cis–trans–trans\n(<b>ctt</b>) (<b>14</b>) trispirocyclotriphosphazenes\nwere obtained from the reactions of <b>3</b> and <b>5</b> and <b>4</b> and <b>6</b> with <i>N</i>-methyl-1,3-diaminopropane. <i>cis</i>-Dispirocyclotriphosphazenes (<b>3</b> and <b>5</b>) exist as “pseudomesoracemates”, while <i>trans</i>-dispirocyclotriphosphazenes (<b>4</b> and <b>6</b>) are in “racemates”. The existences of <b>cis</b>-<b>3</b> and <b>trans</b>-<b>4</b> as\n“pseudomesoracemate” and “racemate” were\nconfirmed by <sup>31</sup>P NMR spectra recorded by the addition of\n“chiral solvating agent (<b>CSA</b>)”. X-ray crystallography\nproved that the absolute configurations of each enantiomer of <b>cis-5</b> and <b>trans-6</b> are SS′ and RS′.\nTrispirocyclotriphosphazenes <b>tct</b>, <b>ttc</b>, <b>ccc</b>, and <b>ctt</b> exist as racemates, pseudomesoracemate,\nand meso forms. Furthermore, Hirshfeld surface analysis of the crystal\nstructures of <b>cis</b>-<b>5</b> and <b>trans</b>-<b>6</b> revealed that the most significant contribution to\ncrystal packing comes from H···H (58.2 and 57.6%, respectively).\nAn oxidation–reduction wave was detected in the reversible\ncyclic voltammograms of the phosphazenes. The highest power conversion\nefficiency in dye-sensitized solar cell studies was obtained with <b>cis</b>-<b>5</b>. Additionally, <b>trans</b>-<b>6</b> exhibited the lowest minimal inhibitory concentration value\n(78.1 μM) against Candida tropicalis, and it was observed to cleave pBR322 plasmid DNA.