1000-Fold Enhancement of Luminescence Lifetimes via Energy-Transfer Equilibration with the T₁ State of Zn(TPP)

Abstract

The new zinc porphyrin/tungsten alkylidyne dyad Zn(TPP)-C[triple bond]CC(6)H(4)C[triple bond]W(dppe)(2)Cl (1) possesses novel photophysical properties that arise from a tunable excited-state triplet-triplet equilibrium between the porphyrin and tungsten alkylidyne units. Dyad 1 exhibits (3)(d(xy) <-- pi*(WCR)) phosphorescence with a lifetime that is 20 times longer than that of the parent chromophore W(CC(6)H(4)CCPh)(dppe)(2)Cl (2). The triplet-triplet equilibrium can be tuned by the addition of ligands to the Zn center, resulting in phosphorescence lifetimes for 1(L) that are up to 1300 times longer than that of 2. The "lifetime reservoir" effect exhibited by 1(L) is approximately 1 order of magnitude larger than previously reported examples of the phenomenon.

Photoinduced Charge Separation in Zinc–Porphyrin/Tungsten–Alkylidyne Dyads: Generation of Reactive Porphyrin and Metallo Radical States

“…Properties and kinetics of the S 1 product states : The decay of the S 1 states of ZnTPP( 1 ) and ZnTP Cl P( 1 ) results in formation of the ground state and three excited states: the porphyrin‐centered T 1 state, the 3 [dπ*] state of subunit 1 , and the [ZnPor − ][ 1 + ] charge‐separated state. The T 1 state lies highest in energy (Figure 7); therefore, it could decay to the 3 [dπ*] state through triplet–triplet energy transfer, as observed previously for a covalently linked zinc–porphyrin/tungsten–alkylidyne analogue of ZnPor( 1 ),30 and/or by charge separation to the [ZnPor − ][ 1 + ] state, as well as by internal conversion to the ground state. However, the T 1 states of the dyads are not observed to decay during the time frame of the transient‐absorption experiment (Δ t =3 ns, Figures 4 and 5), and the spectra are complicated by the presence of the T 1 bands of free ZnPor.…”

“…Toluene (Burdick & Jackson, high-purity grade) was stored over NaK (1:2) alloy, from which it was transferred under vacuum. The compounds [WCl(C-4,4'-C 6 H 4 CCC 5 H 4 N)-A C H T U N G T R E N N U N G (dppe) 2 ] (1), [12] [WCl(C-4-C 6 H 4 CCPh)A C H T U N G T R E N N U N G (dppe) 2 ] (2), [30] and [5,10,15,20-tetra(p-chlorophenyl)porphyrinato]zinc (ZnTP Cl P) [22] were prepared according to standard methods. [5,10,15,20- Fluorescence lifetime measurements: Fluorescence lifetimes were measured with a ChronosBH time-domain fluorometer (ISS, Inc.) using timecorrelated single photon counting methods.…”

Harnessing Reversible Electronic Energy Transfer: From Molecular Dyads to Molecular Machines

“…Az inc tetraphenylporphyrin, Zn(TPP),b earing an adjacent tungsten alkylidyne moiety (20)w as shown to undergo REET resulting in a > 1000-fold luminescence lifetime augmentation in specific cases. [28] The enhanced lifetimeo ft he dyad (20 times that of the parent) can be accounted for by at hermale quilibrium between the emissive 3 (d xy ! p*) state of the tungsten fragment and the longer-lived (t = 1.25 ms), nonemissive T 1 state of the porphyrin moietyw hich is in close proximity (DE = ca.…”

“…Te mperature-dependent transienta bsorption spectroscopy permitted energy gap determination( 1740 cm À1 )b etween the MMLCT and PNI triplet states alongw ith the time constants associated with the interconversion betweene xcited states, which decayed to the ground state with at ime constant of 65 ms. Zhao and Zhang reported another example where at riplet equilibrium was proposed between aP ta nd ar ylene dye. [36] Ar ange of spirobifluorene bridged heteroleptic mono-and trinuclearc omplexes comprising Pt II ,O s II and Ir III metalsw ere described (26)(27)(28). [37] Here, the luminescence of the tetrad consisting of spirobifluorene-bridgedP t, Ir and Os complexes were studied by comparison with the reference complexes bearing two identical luminophores (Ir or Os) at the periphery.T he 3 M Pt LCT and 3 LC states of the Pt and spiro ligand undergo fast energy transfer into the 3 M Ir LCT or the 3 M Os LCT state in the Pt-M 2 (M = Ir or Os) arrays, while 3 LC and 3 M Pt LCT states serve as energy reservoirs for the quasi-isoenergetic metal excited states, resulting in ae xtended excited state lifetimei nt he arrays.…”

Prolonging the Emissive Lifetimes of Copper(I) Complexes with 3MLCT and 3(π–π*) State Equilibria – A Fluorene Moiety as an “Energy Reservoir”

“…This strategy was first reported by Ford and Rodgers and has been demonstrated in Ru II and Ir III diimine complexes but has rarely been reported for Cu I complexes , . In addition, it is worth noting that the reported chromophores are mostly centered on pyrene, anthracene, and naphthalimide, whereas the exploration of energy reservoirs suitable for use with other organic chromophores remains very limited , …”