The mysterious blue emission around 440 nm in carbonyl‐based aliphatic clusteroluminogens

Abstract

Nonconjugated and nonaromatic heteroatoms-based structures are discovered with visible emission at clustering state, namely clusteroluminogens (CLgens).Such kind of luminescence is termed clusteroluminescence (CL) which could not be explained by the traditional molecular photophysical theories constructed upon through-bond conjugation, so investigation on CL has great theoretical significance. In this perspective, we summarize a general feature for C═O bond-based CLgens that a magic blue emission around 440 nm widely exists in different systems such as natural protein, polyamide, polyester, and polyketone. Comprehensive analysis of the reported works suggests that the (n, π*) transition of carbonyl group most likely generates the 440 nm CL. This perspective aims to draw researchers' attention to the common features and general photophysical theories of CL, and shine new light on aggregate photophysics.

Aliphatic Polyesters with White-Light Clusteroluminescence

“…The maximum PL peak is at 460 nm which is the typical n−π* transition peak of isolated C�O groups according to our previous results. 46,47 Meanwhile, the PL spectra of P1∼P6 both in DCM and solid state (Figures 2B and S69−S70) show a clear excitation-dependent emission (EDE) effect with the transformation from dominant shortwavelength emission (∼460 nm) to negligible long-wavelength emission (∼530 nm). Concentration-dependent PL spectra and excitation-spectra of P2 in DCM were measured and show a similar clusterization-triggered emission (CTE) effect that PL intensity is enhanced with concentration (c) increasing from 10 −5 M to 10 −1 M (Figures 2C and S71).…”

Hydrogen-Bonding-Induced Clusteroluminescence and UCST-Type Thermoresponsiveness of Nonconjugated Copolymers

“…Because the carboxylic acid group of AAc is a strong hydrogen donor while the amide group of NVCL can act as hydrogen acceptor, their copolymers can form stable intrachain and interchain H-bonds. The rigidity of the polymer chains is thus improved, which facilitates the n−π* transition of the carbonyl groups and provides a characteristic emission around 440 nm. − …”

“…Meanwhile, the absorbance peak at ∼270 nm and PL peak at ∼440 nm also ascend with the concentration (Figures b,c and S3a,b). These facts suggest that π–π* and n−π* interactions between the heteroatoms on the copolymers are enhanced with higher density of polymer–polymer H-bonds at higher concentration. , We also investigated the effect of nonsolvent on the fluorescence of polymer solutions (Figure S5). With the addition of dibutyl ether (DBE), the nonsolvent, into the DMF solution of the copolymer, the fluorescence intensity of the polymer mixed solution first increased until the volume fraction of DBE reached 25% and then decreased suddenly.…”

Long-lived room temperature phosphorescence from amorphous non-traditional intrinsic clusteroluminescence polymers

“…Based on the above results, the mechanism leading to EDE is proposed as shown in Scheme 1. When the concentration is lower than CCC, no cluster is formed, and the TSI-n-p of the adjacent carbonyl units similar to the single-molecular state is dominant, 49 showing the EIE phenomenon. At high concentrations, in addition to the TSI-n-p of adjacent carbonyl units, there exist diverse clusters with different conjugation degrees owing to the carbonyl clusters 43,44 and the interactions of phenyl groups.…”