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

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