Platinum Complexes of N,N′,N″,N‴-Diboronazophenines

Abstract

Azophenine, (α-CHNH)(CH-N═CH═N-CH), well known to be non-emissive, was rigidified by replacing two amine protons by two difluoroboranes (BF) and further functionalized at the para-positions of the phenyl groups by luminescent trans-ArC≡C-Pt(PR)-C≡C ([Pt]) arms [Ar = CH (R = Et), hexa(n-hexyl)truxene) (Tru; R = Bu)]. Two effects are reported. First, the linking of these [Pt] arms with the central azophenine (CH-N═CH(NH)═N-CH; Q) generates very low energy charge-transfer (CT) singlet and triplet excited states (([Pt]-to-Q)*) with absorption bands extending all the way to 800 nm. Second, the rigidification of azophenine by the incorporation of BF units renders the low-lying CT singlet state clearly emissive at 298 and 77 K in the near-IR region. DFT computations place the triplet emission in the 1200-1400 nm range, but no phosphorescence was detected. The photophysical properties are investigated, and circumstantial evidence for slow triplet energy transfers, Tru* → Q, is provided.

Planar, Stair‐Stepped, and Twisted: Modulating Structure and Photophysics in Pyrene‐ and Benzene‐Fused N‐Heterocyclic Boranes

“…The system, which indeed contains two BF 2 units, can be best described as az witterionic molecule with two positive charges delocalized over the benzene core and an egative chargel ocalizedo ne ach boron atom.T his interpretation is furthers upported by the bond lengths of C1ÀC2 [1.3968 12]a nd C1ÀC3' [1.5062 12] which suggest that the p-electrons are delocalized across the N1-C1-C2-C3-N2 atoms and not within the central 6-membered ring. This description is also consistent with reportedb is(boron difluoride) complex [(BF 2 ) 2 (m-4-EtAp)] (Ap = azophenine), [28] platinum N',N',N',N''-diboronazopheninec omplexes, [29] and the [(ttmgb)(BF 2 ) 2 ](BF 4 ) 2 (ttmgb = 1,2,3,4-tetrakis(tetramethylguanidinyl)benzene) salt. [30] Additionally,t he BÀFb ond lengths [1.3906 (12) and 1.3853 (12) ]a re slightly longert han the B1À F1 bond [1.335(4) ]i nt he pyrene complex 3.…”

Cross Conjugated Organometallic Polymers Exhibiting Ultrafast Excitation Energy Channeling: Drastic Effect of the Connectivity

“…This effect promotes mixing of the spin and electronic wavefunctions, thus rendering the singlet and triplet less pure and consequently the selection rules for the change in state multiplicity less rigorous. Moreover, a recent investigation on a related diboroazophenines (a rigidified quinone diimine by two N ‐BF 2 ‐ N cycles) flanked by four C 6 H 4 CCPt(PBu 3 ) 2 CCPh arms, was found fluorescent from their CT S 1 state ( 1 ( [Pt] → azophenine)*) with τ F values of 22.6 [298] and 96.8 ps [77 K]) . This similarity is interesting.…”