In:
Chemistry – A European Journal, Wiley, Vol. 25, No. 72 ( 2019-12-20), p. 16755-16764
Kurzfassung:
With the aim of generalizing the structure–properties relationship of bending heterocyclic molecules that undergo prominent photoinduced structural planarization (PISP), a series of new dihydrodibenzo[ ac ]phenazine derivatives in which one nitrogen atom is replaced by oxygen ( PNO ), sulfur ( PNS ), selenium ( PNSe ), or dimethylmethanediyl ( PNC ) was strategically designed and synthesized. Compounds PNO , PNS , and PNSe have significantly nonplanar geometries in the ground state, which undergo PISP to give a planarlike conformer and hence a large emission Stokes shift. A combination of femtosecond early relaxation dynamics and computational approaches established an R*→I* (intermediate)→P* sequential kinetic pattern for PNS and PNSe , whereas PNO undergoes R*→P* one‐step kinetics. The polarization ability of the substituted heteroatoms, which is in the order O 〈 S 〈 Se, correlates with their increase in π conjugation, and hence the Stokes shift of the emission is in the order PNO 〈 PNS 〈 PNSe . Compound PNSe with the largest PISP barrier was shown to be a highly sensitive viscosity probe. Further evidence for heteroatom‐harnessing PISP is given by PNC , in which the dimethylmethanediyl substituent lacks lone pair electrons for π extension, showing the normal emission of the bent structure. The results led to the conclusion that PISP is ubiquitous in dihydrodibenzo[ ac ]phenazines, for which the driving force is elongation of the π delocalization to gain stabilization in the excited state.
Materialart:
Online-Ressource
ISSN:
0947-6539
,
1521-3765
DOI:
10.1002/chem.201904900
Sprache:
Englisch
Verlag:
Wiley
Publikationsdatum:
2019
ZDB Id:
1478547-X
