Solvatochromism of Distyrylbenzene Pairs Bound Together by [2.2]Paracyclophane:  Evidence for a Polarizable “Through-Space” Delocalized State

Abstract

A series of compounds were designed and synthesized to examine how through-space and through-bond electron delocalization respond to solvent effects. The general strategy involves the study of "dimers" of the distyrylbenzene chromophore held in close proximity by the [2.2]paracyclophane core and a systematic dissection of the chromophore into components with through-space and through-bond electronic delocalization. Steady state and time-resolved fluorescence spectroscopy in a range of solvents reveals a red-shift in emission and an increase in the intrinsic fluorescence lifetime for the emitting state in polar solvents when donor substituents are absent. We propose that through-space delocalization across the [2.2]paracyclophane core is more polarizable in the excited state, relative to the through-bond (distyrylbenzene based) excited state. When strong donors are attached to the distyrylbenzene chromophore, the charge transfer character of the distyrylbenzene-based excited state dominates fluorescence properties.

Prediction of Excitation Energies for Conjugated Oligomers and Polymers from Time-Dependent Density Functional Theory

“…The total blueshift when going from LSDA to PBE0 (functional with 25% portion of the exact orbital exchange) is about 0.8 eV. Due to nearly non-polar structure of the molecule, we observe a fairly small solvatochromic shift [115] of about 50 meV. The calculated PBE0 value for the excitation energy in chloroform, 3.40 eV, agrees well with the experimental maximum (3.48 eV) of the lowest absorption peak.…”

Probing excited state electronic communications across diethynyl-[2.2]paracyclophane-containing conjugated organometallic polymers

“…The time-resolved spectra do not show obvious appearance of two distinct bands, which is inherent to the large bandwidth of the emission, but the position of these bands is very similar between the polymers and complexes (see below). The t e data for 2 and 3 are in line with those reported for trans-Pt(PEt 3 ) 2 (CRCAr) 2 15 (Ar = 2,4,6-Me 3 C 6 H 2 , t e = 85.2 AE 0.5 ms; 2,4,5-Me 3 C 6 H 2 , t e = 49.9 AE 0.5 ms, in 2-MeTHF/77 K) and Pt 2 (dppm) 2 (CRCPh) 2 (t e = 5.60 AE 0.10 ms, in 2-MeTHF/77 K). 16 The Pt 2 (dppm) 2 -(CRC(2,4,5-Me 3 C 6 H 2 )) 2 complex was also prepared.…”

“…7, 10 The emission spectrum of 1 shows a fluorescence (360, t F o 1 ns) and a phosphorescence (520 nm) at positions matching those of 6, implying that the nature of the excited state is the same (pp*). Also, the emission spectra of 2 and 3 are similar to those for trans-Pt(PEt 3 ) 2 (CRCPh) 2 15 and Pt 2 (dppm) 2 (CRCPh 2 ) 2 . 16 Based on the Stokes shifts (D) and emission lifetimes (t e ), these emissions are fluorescence at 370 nm (D = 800 cm À1 , t e o 1 ns) for 2, and phosphorescence at 505 nm (D = 8000 cm À1 , t e > 1 ms) for 2 and at 645 nm (8300 cm À1 , D > 1 ms) for 3.…”

From the Decks to the Bridges: Optoelectronics in [2.2]Paracyclophane Chemistry

“…[22][23] The related neutral pCps were also studied. The disubstituted pair was studied to investigate the effect of charge with direct comparison to pCp.…”