Tuning the Photophysical Properties of Symmetric Squarylium Dyes: Investigation on the Halogen Modulation Effects

Abstract

As eries of symmetric squarylium dyes (SQDPA-X) with different halogen (X = F, Cl, Br,I )s ubstituents have been developed.T he photophysical properties could be facilely tuned by the halogen modulation effects. The strategyo fi ncorporating different halogen substitutions into AIE activel uminogens enables af acile approachf or exploring new intriguing organicf luorescent dyes.Organicf luorescent dyes have gained increasing interesto n account of their substantial applicationsi no rganic light-emitting diodes, [1] bioimaging, [2] dye-sensitized solarc ells, [3] nonlinear optical materials, [4] etc. It is known that most of the luminophores usually tolerate ap ronounced decreasing of their fluorescence in aggregated states, known as aggregation caused quenching (ACQ)e ffect. [5] In contrast, some particular chromophores are emissive in the aggregated states. This unconventional photophysical phenomenon is coined as aggregation-induced emission (AIE) by Ta ng and co-workers. [6] The comprehensivem echanism for the unique phenomenon was clarified to be the restriction of intramolecular rotations (RIR). [7] Mosto f AIE activel uminogens(AIEgens) possessp ropeller-like or flexible moieties such as diphenylamine, [8] triarylamine, [9] tetraphenylethylene, [10] and so forth. Currently,e xcept for the abovementioned applications, AIEgen-based stimuli-responsive fluorochromic materials [11] have also been developed. [12] Fluorochromicm aterials with reversiblec olor changet riggered by external stimuli are an important category of smart materials. [13] Up to now,s everalt ypes of fluorochromic materials have been developed such as photochromic, [14] electrochromic, [15] thermochromic, [16] mechanochromic, [17] solvatochromic, [18] and vapochromic [19] materials. Among them, mechano-chromic materials with reversiblef luorescence change by mechanical stress have made rapid progress. [20] Squaric acid is an electron-deficient motif with af our membered ring that can react with electron-donatingg roups to form ad onor-acceptor-donor (D-A-D) system. [21] Theoretical simulation suggests that the ground state and excited singlet state of squarylium dyes (SQDs) exhibit distinctive intramolecular charget ransfer (ICT) behavior. [22] To the besto fo ur knowledge,S QDs with both AIE and fluorochromic properties have not yet been explored. In this context, we herein reported a new series of symmetric SQDs derivatives (i.e.,S QDPA-F, SQDPA-Cl, SQDPA-Br,S QDPA-I) with typical AIE, mechanochromic and vapochromicp roperties by differenth alogen (X = F, Cl, Br,I )m odulation effects (Scheme 1). These SQDsw ere ambiguously characterizedb yU V/Vis absorption spectroscopy, powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), single crystal diffraction analysis and theoretical modelling.The SQDs weref acilelys ynthesizedb yt he condensation of squaric acid with diphenylamine derivatives in toluene and nbutyla lcohol at 110 8C( Scheme 1). [23] The photophysical properties of all SQDs was first investigated by UV/Vis spect...

Emission-Tunable Soft Porous Organic Crystal Based on Squaraine for Single-Crystal Analysis of Guest-Induced Gate-Opening Transformation

“…The intrinsic oxygen atoms in the skeleton of squaric acid can act as natural functional sites for framework construction and selective molecular recognition through hydrogen bonds (H bonds) or Lewis acid/base interactions with special guest species, without the need for postsynthetic modification . In addition, a variety of squaraines (SQs) dyes derived from squaric acid exhibit favorable photophysical properties with intense absorption and emission in the wide range from visible to near infrared, which are sensitive to the surrounding environment. , Recently, a new type of SQs have been reported to exhibit unique solid-state tunable luminescence properties, which can be modulated through control of molecular excited-state vibration and electron behavior . Some of these SQs could achieve temperature-/solvent vapor-triggered SCSC reversible structure transformation associating with tunable luminescence behavior, , implying their structural flexibility and structure-related luminescence.…”

Visible light-induced cationic photopolymerization by diphenyliodonium hexafluorophosphate and benzothiadiazole dyes

“…The synthetic route of Y-1 and Y-2 is shown in Scheme 1. The intermediates 1 and 2 are prepared according to literatures [34][35][36][37].…”

Effects of Halogenation on Quinoline‐Malononitrile‐based AIEgens: Photophysical Properties Investigation and Wash‐Free Imaging

“…On the other hand, halogenation is a feasible strategy to influence the photophysical properties of organic dyes, such as photostability, molecular packing, emission efficiency, and so on [38–48] . Some studies have also been conducted and reported to investigate the effects of halogen substitutions on AIEgens [49–55] .…”