Abstract
Metal–bridged polcyclic aromatic complexes, exhibiting unusual optical effects such as near-infrared photoluminescence with particularly large Stokes shifts, long lifetimes and aggregation enhancement, have been established as unique “carbonloong chemistry”. Herein, the electronic structures, aromaticities, absorption spectra and third order nonlinear optical (NLO) responses of metal–bridged polcyclic aromatic complexes (M = Fe, Re, Os and Ir) are investigated using the density functional theory computations. It is found that the bridge–head metal can stabilize and influence rings, thus creating π–, σ– and metalla–aromaticity in an extended, π–conjugated framework. Interestingly, metal radius greatly influence the bond, aromaticity, liner and third order NLO properties, which reveals useful information to develop new applications of metal regulatory mechanism in NLO materials field. Significantly, the novel relationship between the aromaticity and third order NLO response has firstly been proposed, that the metal-bridged polycyclic complex with larger aromaticity will exhibit larger third order nonlinear optical response. It is our expectation that the novel link between aromaticity and NLO response could provide valuable information for scientists to develop the potential NLO materials on the basis of metal–bridged polycyclic complexes.
Highlights
Aromaticity is still one of the central and compelling topics that has long interested both experimentalists and theoreticians because of its fascinating and constantly growing diversity[1,2,3,4]
To elucidate the bonding and electronic structures of these unique pentadentate carbon chain chelates, the structure optimization was performed on B3LYP/def2-TZVPP
For metal–bridged polcyclic complex, the aromaticity was attributed to Craig–Möbius topology which favours 4n π–electron conjugation counts
Summary
Aromaticity is still one of the central and compelling topics that has long interested both experimentalists and theoreticians because of its fascinating and constantly growing diversity[1,2,3,4]. The seminal proof-of-concept work on Craig-Möbius aromaticity in planar metallacycles was reported by Mauksch and Tsogoeva[9]. It first presented the building principles for Craig-Möbius aromatics and with transition metals from group 8 (Fe, Ru, Os). Metal–bridged tricyclic aromatic complex (3*[Os]) was reported through the stabilization of two typically antiaromatic frameworks (cyclobutadiene and pentalene) by introducing a metal[28]. 6*[Os] was surrounded with the completion of a metal–bridged polycyclic aromatic system, in which all of the five coordinated carbons lie in the equatorial plane It is the largest planar Möbius aromatic system synthesized to date[30,31,32,33]. The particular aim of the present paper is to propose the novel relationship between the aromaticity and NLO response
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