Restricted Photoinduced Conformational Change in the Cu(I) Complex for Sensing Mechanical Properties

Abstract

When designing photoresponsive materials, the impact of a polymer host matrix on the photophysical and photochemical properties of chromophores can be dramatic and advantageous for correlating macromolecular properties. Some compounds possess changes in their photophysical response with variation in the surrounding media (e.g., crystalline glass vs solution). This study demonstrates how changes in the excited state dynamics of [Cu(dmp) 2 ] + , where dmp = 2,9-dimethyl-1,10-phenanthroline, are used to quantitatively probe the viscosity of the surrounding polymer matrix. A correlation of both excited state lifetime and photoluminescence emission wavelength on viscosity was observed in different supramolecular materials containing [Cu(dmp) 2 ] + . These effects were attributed to restricted photoinduced structural distortion of the Cu(I) complex as the polymer matrix hardened. This photoluminescence sensor features a greater dynamic range for viscosity sensing (6 orders of magnitude) and displayed larger changes in lifetime response with respect to typical organometallic mechanosensitive probes.

Surface immobilized copper(i) diimine photosensitizers as molecular probes for elucidating the effects of confinement at interfaces for solar energy conversion

“…This trend is similar to that previously observed for Cu(I)(dmp) 2 dispersed into a polymer matrix where the 3 MLCT lifetime increased from 90 ns in CH 2 Cl 2 to 210 ns with increasing polymer viscosity. 35 We interpret our results in a similar fashion: as 3 is immobilized in increasingly smaller pores and in closer proximity to other immobilized Cu centres (as measured by EPR), the typical flattening distortion is restricted which increases the lifetime of the excited state.…”

Heteroleptic Copper(I) Complexes Prepared from Phenanthroline and Bis-Phosphine Ligands: Rationalization of the Photophysical and Electrochemical Properties

“…Copper(I) complexes equipped with a suitable ligand environment may exhibit long-lived excited states and strong luminescence, which makes them increasingly important for electroluminescent devices, 1,2 photoredox catalysis, 3,4 solar-tofuels conversion, 5−8 and sensing. 9,10 A great deal of work has been devoted to the study of homoleptic [Cu(NN) 2 ] + complexes (where NN denotes diimmine ligands, typically, substituted 1,10-phenanthrolines). 11,12 In most cases, these compounds are weak emitters both in solution and in the solid state, due to extensive excited state structural rearrangements 13 that can be traced by ultrafast absorption 14,15 and X-ray spectroscopy.…”

“…Copper­(I) complexes equipped with a suitable ligand environment may exhibit long-lived excited states and strong luminescence, which makes them increasingly important for electroluminescent devices, , photoredox catalysis, , solar-to-fuels conversion, − and sensing. , A great deal of work has been devoted to the study of homoleptic [Cu­(NN) 2 ] + complexes (where NN denotes diimmine ligands, typically, substituted 1,10-phenanthrolines). , In most cases, these compounds are weak emitters both in solution and in the solid state, due to extensive excited state structural rearrangements that can be traced by ultrafast absorption , and X-ray spectroscopy. , Upon light irradiation, the ground-state quasi-tetrahedral geometry undergoes flattening distortions that promote nonradiative deactivations. When phenanthroline ligands are equipped with multiple bulky substituents (as a matter of fact, very limited cases), strong luminescence may be detected also for [Cu­(NN) 2 ] + compounds. − …”

Enhancing the Visible-Light Absorption and Excited-State Properties of Cu(I) MLCT Excited States

“…A recent example takes advantage of this photoinduced structural distortion and its resulting photoluminescence to estimate the rheological properties of macromolecules. 17 Other research targeted the preparation of molecules that exaggerated this structural permutation by using 2,9-phenyl substituents to severely predistort the ground state toward the lowest MLCT excited-state configuration. 11,18−20 The former strategy produced molecules with substantial Stokes shifts that ultimately wasted most of the optical input energy by permitting too much excited-state distortion.…”

“…Initial molecular strategies intended to impede these transient structural rearrangements targeted homoleptic cuprous bis-(1,10-phenanthroline) (phen) complexes containing steric encumbering alkyl-bearing 2,9-substituents. , These ligand modifications aided in suppressing the pseudo-Jahn–Teller flattening distortion accompanying the formation of Cu­(II) following visible-light excitation. A recent example takes advantage of this photoinduced structural distortion and its resulting photoluminescence to estimate the rheological properties of macromolecules . Other research targeted the preparation of molecules that exaggerated this structural permutation by using 2,9-phenyl substituents to severely predistort the ground state toward the lowest MLCT excited-state configuration. ,− The former strategy produced molecules with substantial Stokes shifts that ultimately wasted most of the optical input energy by permitting too much excited-state distortion.…”