Premium
Reaching Optimal Light‐Induced Intramolecular Spin Alignment within Photomagnetic Molecular Device Prototypes
Author(s) -
Ciofini Ilaria,
Adamo Carlo,
Teki Yoshio,
Tuyèras Fabien,
Lainé Philippe P.
Publication year - 2008
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200801405
Subject(s) - intramolecular force , chemistry , ground state , dangling bond , anthracene , crystallography , stereochemistry , photochemistry , atomic physics , physics , organic chemistry , silicon
Abstract Ground‐state (GS) and excited‐state (ES) properties of novel photomagnetic molecular devices (PMMDs) are investigated by means of density functional theory. These organic PMMDs undergo a ferromagnetic alignment of their intramolecular spins in the lowest ES. They are comprised of: 1) an anthracene unit (An) as both the photosensitizer (P) and a transient spin carrier (SC) in the triplet ES ( 3 An*); 2) imino‐nitroxyl (IN) or oxoverdazyl (OV) stable radical(s) as the dangling SC(s); and 3) bridge(s) (B) connecting peripheral SC(s) to the An core at positions 9 and 10. Improving the efficiency of the PMMDs involves strengthening the ES intramolecular exchange coupling ( J ES ) between transient and persistent SCs, hence the choice of 2‐pyrimidinyl (pm) as B elements to replace the original p ‐phenylene (ph). Dissymmetry of the pm connectors leads to [SC‐B‐P‐B‐SC] regio‐isomers int . and ext., depending on whether the pyrimidinic nitrogen atoms point towards the An core or the peripheral SCs, respectively. For the int . regio‐isomers we show that the photoinduced spin alignment is significantly improved because the J ES / k B value is increased by a factor of more than two compared with the ph‐based analogue ( J ES / k B >+400 K). Most importantly, we show that the optimal J ES / k B value (≈+600 K) could be reached in the event of an unexpected saddle‐shaped structural distortion of the lowest ES. Accounting for this intriguing behavior requires dissection of the combined effects of 1) borderline intramolecular steric hindrance about key An–pm linkages, which translates into the flatness of the potential energy surface; 2) spin density disruption due to the presence of radicals; and 3) possibly intervening photochemistry, with An acting as a light‐triggered electron donor while pm, IN, and OV behave as electron acceptors. Finally, potentialities attached to the [(SC)‐pm‐An‐pm] int pattern are disclosed.