Intramolecular Charge Transfer Absorption Band Research Articles

Exploring solvatochromism: a comprehensive analysis of research data of the solvent -solute interactions of 4-nitro-2-cyano-azo benzene-meta toluidine

This study investigates the solvatochromic behavior of a new D1 disperse dye, focusing on the 4-nitro-2-cyano-azo-Benzene-metaToluidine type. Using UV-visible spectroscopy, we analyze the dye’s performance in single solvents and binary mixtures. Our analysis includes the evaluation of solvent polarity parameters and dye structure parameters, with emphasis on the longest wavelength intramolecular charge transfer absorption band. We identify nonlinear and linear patterns in the electronic transition energies plots with respect to solvent composition. Statistical analysis considers correlation coefficients, root mean squared error, mean absolute percentage error, and other parameters, providing insights into data accuracy and precision. This experimental and statistical study explores the absorption spectrum, wavelength characteristics, absorption energy, and polarity of a novel azo dye across various solvent and solute environments. These findings contribute to a comprehensive understanding of the dye’s photophysical and photochemical properties, potentially enabling applications in optical sensors and advanced materials.Graphical abstract

Nitrogen-bridged star-shaped fused-ring electron acceptors for organic solar cells

Two kinds of nitrogen-bridged star-shaped fused-ring electron acceptors based on benzo[1,2-b:3,4-b’-5,6-b’’]tri(4-H-dithieno[3,2-b:2’,3’-d]pyrrole) (BTDTP) core with linear and branched alkyl side chains on bridging nitrogen atoms are developed. Both electron acceptors exhibit strong intramolecular charge transfer absorption bands at 500–800 nm (molar extinction coefficient of 3.0 × 105 M −1 cm−1) with narrow optical bandgaps around 1.58 eV, but reveal different molecular packing and morphology. Compared to acceptor with linear side chains, the acceptor bearing branched side chains exhibits ordered face-on orientation with tight π-π stacking, as well as more favorable phase separation morphology and balanced charge transport when blended with polymer donor PM6. Organic solar cell device based on acceptors bearing branched side chains achieves a power conversion efficiency (PCE) of 9.95% with a fill factor of 74.98% and a short-circuit current density of 14.90 mA cm−2, which is much superior to the device using acceptors bearing linear side chains (a PCE of 6.74%).

Synthesis, Structure, and Significant Energy Gap Modulation of Symmetrical Silafluorene-Cored Tetracyanobutadiene and Tetracyanoquinodimethane Derivatives.

A series of symmetrical tetracyanobutadiene and tetracyanoquinodimethane derivatives with a D-A-D'-A-D structural configuration and silafluorene core (D') were designed and readily synthesized via a [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction. We found that the photophysical properties and HOMO and LUMO energy levels and gaps of the silafluorene derivatives could be profoundly remolded through CA-RE reactions and modulated by varying the peripheral donor units from phenyl, m-dimethoxyphenyl, and N,N-dimethylaniline to triphenylamine groups. After CA-RE reactions, the HOMO-LUMO gaps of 1a-1j are in the range of 1.75-2.78 eV, with significant decreases of 0.52-1.46 eV compared to those of the parent silafluorene compounds 2a-2j. The intriguing crystal structures of 1f and 1j were analyzed and elucidated to show their unique potential porosity. The stability, electrochemical, and computational studies were systematically performed to unveil the reshaped electron-donating and -withdrawing nature in one molecular system. 1h-1j with peripherally strong amino donors exhibit an intense and broad intramolecular charge transfer absorption band in the near-infrared region from 550 to 900 nm. The molecular design and synthesis reported here broaden the types and fields of D-A molecular systems for potential applications in organic optoelectronic devices.

Heavy-Atom-Free Bay-Substituted Perylene Diimide Donor-Acceptor Photosensitizers.

Perylene diimide (PDI) dyes are extensively investigated because of their favorable photophysical characteristics for a wide range of organic material applications. Fine-tuning of the optoelectronic properties is readily achieved by functionalization of the electron-deficient PDI scaffold. Here, we present four new donor-acceptor type dyads, wherein the electron donor units - benzo[1,2-b : 4,5-b']dithiophene, 9,9-dimethyl-9,10-dihydroacridine, dithieno[3,2-b : 2',3'-d]pyrrole, and triphenylamine-are attached to the bay-positions of the PDI acceptor. Intersystem crossing occurs for these systems upon photoexcitation, without the aid of heavy atoms, resulting in singlet oxygen quantum yields up to 80 % in toluene solution. Furthermore, this feature is retained when the system is directly irradiated with energy corresponding to the intramolecular charge-transfer absorption band (at 639 nm). Geometrical optimization and (time-dependent) density functional theory calculations afford more insights into the requirements for intersystem crossing such as spin-orbit coupling, dihedral angles, the involvement of charge-transfer states, and energy level alignment.

Novel 1,5-naphthyridine-chromophores with D-A-D architecture: Synthesis, synthesis, luminescence and electrochemical properties

A series of symmetrical 1,5-naphthyridine compounds with donor-acceptor-donor (D-A-D) architecture and different chromophores were synthesized and characterized. Their thermal, optical and electrochemical properties were investigated systematically. These compounds show robust thermal property with high phase transition temperatures (above 247 °C). In addition, all these compounds exhibit intense absorption bands in UV and visible region, which arise from the intramolecular charge transfer (ICT) transition between the donor and acceptor segments. The electron-donating chromophores on the central naphthyridine cause significant bathochromic shifts of the low energy ICT absorption bands. Meanwhile, all compounds are emissive in solution at room temperature (λem = 450–520 nm). When the electron-donating ability of the attached chromophores increases, the fluorescent quantum yields of these compounds increase. The calculated ground-state geometries further demonstrate the ICT transition for these molecules from HOMO to LUMO. Their luminescent and electrochemical properties could be used for understanding the structure-property relationship of naphthyridine compounds and developing optical functional materials.

An Azo Dye Based D‐π‐A Chromogenic Probe for Selective Naked‐Eye Detection of Hg2+ Ion: Application in Logic Gate Operation

AbstractThe current work describes the selective colorimetric detection of metal ions using a simple azo dye (L1) containing donor‐π‐acceptor framework. In this chromogenic probe, salicylaldehyde is used as donor and nitrobenzene group as acceptor unit. L1 is found to show selective recognition of mercuric ion both visually and spectrophotometrically with no interference from environmentally relevant metal ions in DMSO‐water mixture. It exhibits reddish‐pink colour in DMSO‐water medium as a result of intramolecular charge transfer (ICT) from the electron donating phenolic group to electron withdrawing nitrobenzene group. It selectively binds with Hg2+ even in presence of other interfering metal ions and form a 1 : 1 L1‐Hg2+ adduct. It is evident from a change in colour along with a decrease of ICT absorption band and hypsochromic shift of π‐π* band. The binding of the chemosensor and mercuric ion through the salicylaldehyde unit is proved from 1H‐NMR data and DFT calculations. Using UV‐Vis spectroscopic technique the detection limit and binding constant values are calculated to be 6 μM and 3.3 x 103 M−1 respectively. Hg2+ probing process displays reversibility upon addition of fluoride ion. The on‐off‐on colorimetric change on sequential addition of Hg2+ and F− mimics an IMPLICATION type logic gate.

Nonfullerene Acceptor with "Donor-Acceptor Combined π-Bridge" for Organic Photovoltaics with Large Open-Circuit Voltage.

In this work, a kind of "donor-acceptor (D-A) combined π-bridge" based on the regioselective reactivity of monofluoro-substituted benzothiadiazole (FBT) to link a thiophene ring has been designed to construct a new A-π-D-π-A-type small molecular acceptor (IDT-FBTR) with indacenodithiophene (IDT) as a central core (D) and 3-octyl-2-(1,1-dicyanomethylene)rhodanine as an electron-withdrawing terminal group (A). Because of the strong intramolecular push-pull electron effect, the IDT-FBTR shows a strong and broad intramolecular charge-transfer absorption band in the range of 500-750 nm. Especially, as an electron-deficient FBT unit (A') and an electron-rich thiophene ring (D') in "D-A combined π-bridge" exert an "offset effect" to regulate the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy levels of the molecule, a relatively high LUMO energy level can be maintained for IDT-FBTR that is helpful to enhance the open-circuit voltage ( Voc) for highly efficient organic solar cells (OSCs). Therefore, the optimized OSC device based on IDT-FBTR as the acceptor and PTB7-Th as the donor shows a much high Voc of 1.02 V with a relatively low Eloss of 0.56 eV and a best power conversion efficiency of 9.14%.

Rapid and Selective Detection of Cyanide Anion by Enhanced Fluorescent Emission and Colorimetric Color Changes at Micromole Levels in Aqueous Medium

One main source of cyanide (CN−) exposure for mammals is through the plant consumption; thus, the sensitive and selective cyanide detection in plant tissue is a significant and urgent work. Here, a simple sensor N′‐(2,4‐dihydroxybenzylidene)naphtha[2,1‐b]furan‐2‐carbohydrazide (Q1‐3) was designed and synthesized for selective and sensitive dual‐channel detection of cyanide in aqueous medium (DMSO/H2O, 1:9, v/v). Acylhydrazone and phenolic hydroxyl groups on Q1‐3 are the recognition sites, and naphthofuran group is the signal report group. The intramolecular charge transfer between the benzene group and naphthofuran group was impeded because of the electron‐withdrawing groups (hydroxyl) on sensor Q1‐3. Interestingly, the sensor Q1‐3 exhibited an intramolecular charge transfer absorption band at 400 nm and emission band at 500 nm, respectively, directly realizing an “OFF–ON” response after the deprotonation process induced by cyanide anions in aqueous medium (DMSO/H2O, 1:9, v/v). Notably, this sensor was successfully applied to detect cyanide anions in food samples, which proves a very simple and selective platform for on‐site monitoring of cyanide in agriculture samples. In addition, the test strips and silica gel plates based on Q1‐3 were also fabricated, which could act as test kits and silica gel plates for convenient and efficient detection of cyanide anions.

Linear and Nonlinear Optical Properties of Tricyanopropylidene-Based Merocyanine Dyes: Synergistic Experimental and Theoretical Investigations.

New merocyanines dyes with tricyanopropylidene-based acceptor units connected to dihexylaminophenyl or dihexylaminothiophenyl donor moieties through polyenic bridges of different lengths have been designed. All derivatives exhibited a strong dipolar character and showed a typical intramolecular charge transfer (ICT) transition. NMR spectroscopy experiments combined with DFT calculations demonstrated that both the nature of the donor-acceptor pair and the length of the conjugated linker strongly impact the electronic structure of the dyes and induce alteration in the bond-length alternation (BLA) and marked shifts in the ICT absorption bands. Hyper-Rayleigh scattering experiments revealed an exponential increase in the second-harmonic generation response as the polyenic chain length was increased. Strikingly, the largest chromophores with the strongest donor-acceptor pair exhibited a very high first hyperpolarizabilty together with a cyanine-like electronic structure, which apparently contradicts the paradigm of optimal BLA predicted by the two-state model. Although it decreased as the polyenic chain length increased, all dyes also exhibited high thermal stability, which demonstrates their potential for applications in nonlinear optical devices.

Four photoelectroactive composite films based on [BW11O39M(H2O)]7− (M = Zn, Cu) and bipolar hemicyanines

Four composite films consisting of Zn(II) and Cu(II) substituted tungstoborates K7[BW11O39M(H2O)] (BW11M, M=Zn, Cu) and two bipolar hemicyanines of (E)-1,1′-(propane-1,3-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) bromide (H3Br2) and (E)-1,1′-(decane-1,10-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) bromide (H10Br2), were prepared by electrostatic layer-by-layer self-assembly technique. These films of (BW11M/Ha)n (M=Zn, Cu; a=3, 10) exhibited ultraviolet-visible characteristic absorption bands of BW11M and HaBr2 with their absorption intensities increasing linearly with increasing the layer number n, indicating that the composite films were successfully and uniformly deposited. With respect to the H3Br2 and H10Br2 aqueous solutions, the intramolecular charge transfer absorption bands of H3Br2 and H10Br2 in the films exhibited bathochromic shifts to different extents depending on the hemicyanines and BW11M in the films. These films could generate stable, cathodic photocurrents with photocurrent action spectra being consistent with corresponding absorption spectra of the hemicyanines in the films, when illuminated with 100mW/cm2 polychromatic light (730nm>λ>325nm). The effects of the alkyl chain length, BW11M, layer number of the (BW11M/Ha)n films, and applied bias potential and electron acceptor in the electrolyte solution on the photocurrent densities are discussed.

Investigation of Random Copolymer Analogues of a Semi-Random Conjugated Polymer Incorporating Thieno[3,4-b]pyrazine

Semi-random conjugated polymers based on 3-hexylthiophene have been extensively investigated within the past several years as an effective route to broadening absorption without losing desirable properties of poly(3-hexylthiophene) (P3HT). Here, we closely investigate the structural, optical, and electronic differences found in randomized analogues of poly(3-hexylthiophene–thiophene–2,3-dimethylthieno[3,4-b]pyrazine) (P3HTT-TP) semi-random polymers. Proton nuclear Overhauser effect spectroscopy is used to identify linkages within the conjugated backbone, and UV–vis, cyclic voltammetry, and grazing incidence X-ray diffraction are used to determine the influence of the subtle differences in monomer connectivities. Semi-random P3HTT-TP was found to have a stronger intramolecular charge transfer absorption band and higher thermal transitions compared to its randomized analogue. Additionally, the function of the thiophene unit in the semi-random polymers is observed and demonstrated to have key electronic effe...

Unprecedented intramolecular cyclization in strongly dipolar extended merocyanine dyes: A route to novel dyes with improved transparency, nonlinear optical properties and thermal stability

Novel magenta dyes were obtained via an unprecedented base-promoted intramolecular cyclization of strongly dipolar elongated merocyanine dyes bearing a phthalimide substituted tricyanopropylidene terminal segment. These shorter diarylpolyene derivatives retain a dipolar character and show a typical intramolecular charge transfer (ICT) transition. The cyclization noticeably modifies the electronic structure inducing both onset of bond length alternation and reduction of dipole moment as well as a marked hypsochromic and hypochromic shift of the ICT absorption band compared to their merocyanine precursors. Yet the new dyes show improved quadratic hyperpolarizability and thermal stability as compared to the merocyanine dyes having the same number of conjugated double bonds in the polyenic linker. As such these derivatives hold promise as new class of dyes for NLO materials and SHG probes.

Photodetachment spectroscopy of fluorenone radical anions microsolvated with methanol: rationalizing the anomalous solvatochromic behavior due to hydrogen bonding.

The attribution of the extraordinary blue shift for the intramolecular charge-transfer absorption band of fluorenone radical anion solvated in protic media was investigated by means of photodetachment spectroscopy of the gas-phase anions microsolvated with methanol, in conjunction with quantum chemical calculations based on density functional theory. Sequential shifts of the vertical detachment energy as a function of the cluster size are consistent with theoretical predictions, where up to two methanol molecules can directly attach to the carbonyl group. In the photodetachment excitation spectra as alternatives to the photoabsorption spectra, with increasing cluster size, a new absorption band grows in the higher-energy region, which coincides with the blue-shifted band in protic media. Spectral simulations using time-dependent density functional theory with the CAM-B3LYP functional reproduced the feature of the phenomenon. Analyses on the electronic configuration elucidated that the extraordinarily blue shifts originate from energy-level repulsion due to solvation-induced resonant coupling with another electronic state. The orbital transition for the counterpart state corresponds to the first absorption band of the neutral fluorenone molecule, which has small oscillator strength from the ground state. It was found that correction of long-range electron exchange correlation is important for the spectral simulation involving the electronic-state coupling.

Ion sensing by charge transfer absorption variations of benzocrown-bipyridinium conjugates with an alkyl chain.

Two benzocrown ether-bipyridinium conjugates, 1 and 2, each having a different length of alkyl chains with butyl and dodecyl groups, respectively, have been synthesized for the purpose of developing a new guest-responsive color-change chemosensor. Both 1 and 2 showed yellow colors with broad absorption bands around 400 nm in acetonitrile. These are associated with the intramolecular charge transfer (CT) absorption, in which the benzocrown ether and bipyridinium units act as the donor and acceptor, respectively. Upon addition of the guest; such as Na(+), they faded in color due to the blue shift in their intramolecular charge transfer absorption bands. These are associated with the formation of 1:1 host-guest inclusion complex. Analogues, 3 and 4, both being similar in structure to 1 and 2 with non-crown ether unit, also showed intramolecular CT absorptions around 400 nm, but did not change their absorption spectra upon addition of the guest because of the lack of guest-binding abilities. The guest-induced color change of 1 and 2 can be used for alkali and alkaline metal ion sensing. Both 1 and 2 could detect divalent cations such as Mg(2+) and Ca(2+) rather than univalent ones, Li(+), Na(+), K(+), Rb(+), and Cs(+). Although a marked difference between 1 and 2 was not observed in their guest sensing abilities, the remarkable recognition of 1 and 2 for Mg(2+) and Ca(2+) was found compared with that of 5, which has benzyl unit instead of alkyl chains of 1 and 2. The sensitivity values of 1 and 2 were roughly proportional to their binding constants, as shown by the binding constants with Li(+), Na(+), Mg(2+), and Ca(2+) with the values of 910, 260, 820, and 2300 M(-1) for 1 and 930, 290, 1270, and 2790 M(-1) for 2, while the binding constants of 5 were estimated to be 930, 440, 210, and 1200 M(-1) for Li(+), Na(+), Mg(2+), and Ca(2+), respectively. The limit concentration of detection of 2 for Ca(2+) was estimated to be 0.016 mM, which was the smallest value in this system.

Ion-responsive Intramolecular Charge-transfer Absorption Using a Pyridinium Benzocrown Ether Conjugate.

A pyridinium benzocrown ether conjugated compound, 1, and its analogue with a non-crown ether unit, 2, have been prepared. Both compounds showed similar absorption spectra with two absorption bands at around 260 and 330 nm in acetonitrile. The bands at the longer wavelength side are associated with intramolecular charge transfer (ICT) absorption, in which the dialkoxyphenyl unit in benzocrown ether and the pyridinium unit act as the donor and acceptor, respectively. The addition of a guest, such as Li(+) or Mg(2+), caused a blue shift in the ICT absorption band for 1, but not for 2. This is explained by the formation of a 1:1 host-guest inclusion complex of 1 with the guest. The guest-induced absorption variation of 1 can be used for alkali and alkaline metal ion sensing. Compound 1 could detect divalent cations, especially for Mg(2+), rather than univalent ones (Li(+), Na(+), K(+), Rb(+), and Cs(+)), although Li(+) was detected with high sensitivity among the alkali metal ions. Compound 3, which has a pyridyl unit at the para position on the pyridinium of 1, showed a similar trend to that of 1 with lower sensitivity than that of 1. The fact that the Mg(2+)/Li(+) sensitivity ratio of 1 and 3 was estimated to be 8.63 and 5.08, respectively, suggests a higher Mg(2+)-preference of 1 rather than 3, while the Ca(2+)/Na(+) ones were 4.98 and 4.85, respectively, when compared ions with similar ionic radii. The sensitivity values of 1 were roughly proportional to their binding constants, as shown by the binding constants with Li(+), Na(+), Mg(2+), and Ca(2+) with values of 2100, 910, 11500, and 2000 M(-1) for 1, respectively. The binding constants of 3 were estimated to be 1710, 650, 3000, and 1400 M(-1) for Li(+), Na(+), Mg(2+), and Ca(2+), respectively, but could not be obtained for alkaline metal ions. The limit concentration for the detection of 1 for Mg(2+) was estimated to be 0.0156 mM, which was the smallest value in this system.

Improved Photovoltaic Properties of Donor–Acceptor Copolymers by Introducing Quinoxalino[2,3-b′]porphyrin as a Light-Harvesting Unit

Donor–acceptor (D–A) copolymerization is an effective approach to construct low bandgap polymers with tunable electronic energy levels for the application as donor materials in polymer solar cells (PSCs). Usually, D–A copolymers possess an intramolecular charge transfer absorption band at long wavelength direction, so that the absorption of the polymers is broadened. However, absorption at short wavelength direction is also important and should be broadened and enhanced to increase the short-circuit current density (Jsc) of the PSCs. In this study, a series of low bandgap conjugated polymers, P(QP4-BT-DPP1), P(QP1-BT-DPP1), and P(QP1-BT-DPP4), based on two acceptor units quinoxalino[2,3-b′]porphyrin (QP) and diketopyrrolopyrrole (DPP) connected by oligothiophene donor units, were designed and synthesized by palladium-catalyzed Stille-coupling polymerization. As a complementary light-harvesting unit, QP was first introduced into the D–A conjugated polymers for improving the photovoltaic performance of PSCs...

Specific solvatochromism of D–π-A type pyridinium dyes bearing various counter anions in halogenated solvents

Donor–π-acceptor type pyridinium dyes OD1–OD4 bearing various counter anions (X−=Cl−, Br−, I−, or BPh4−) have been designed and developed to gain greater insight into the influences of the electronic structures of D–π-A type pyridinium dye on the specific solvatochromism in halogenated solvents: the intramolecular charge transfer absorption bands of the dyes OD1–OD4 in halogenated solvents show a large bathochromic shift compared with those in the non-halogenated solvents. This study revealed that the halogenated solvents can significantly enhance the intramolecular charge transfer characteristics of D–π-A type pyridinium dye with soft counter anion, leading to large bathochromic shift of absorption band in halogenated solvents, which is in good agreement with an increase in the energy of halogen–halide anion interaction for the type of the halogen atom of halogenated solvents.

Photoinduced intramolecular charge transfer process of betaine pyridinium: A theoretical spectroscopic study

Using Time-Dependent Density Functional Theory and taking into account bulk solvent effects, we investigate the absorption and emission spectra of a betaine pyridinium molecule, the 2-(1-pyridinio) benzimidazolate (SBPa). This molecule exhibits strong photoinduced intramolecular charge transfer (ICT). We have identified two different electronic states involved, respectively, in the strong bathochromic ICT absorption band (S 2) and in the moderate emission band (S 1). The ICT process is analyzed in terms of charge distribution and dipole moment evolutions upon photoexcitation. These results are compared with steady-state spectroscopic measurements.

Influences of protonation and hydrogen bonding on intramolecular charge transfer compounds possessing different spacers

This work investigated the influence of protonation and hydrogen bonding on intramolecular charge transfer (ICT) through different spacers. Three compounds, DS-NH 2 (with a conjugated double bond), TS-NH 2 (with a conjugated triple bond), and SS-NH 2 (with a flexible saturated bond), possessing the same donor group (aniline) and the same acceptor group (naphthalene) but with different linkages were synthesized for this purpose. The double bond and triple bond spacers provided a more efficient ICT pathway than a flexible saturated bond in the ground state, so an ICT absorption band was observed for compounds DS-NH 2 and TS-NH 2. Although SS-NH 2 did not exhibit any ICT absorption band, two kinds of intramolecular exciplex emissions were observed depending on the solvent polarity. The excited-state dipole moment of DS-NH 2 is less than that of TS-NH 2. The ICT absorption and emission bands are quenched by protonation in this system. The influence of hydrogen bonding for DS-NH 2 and TS-NH 2 only occurs in the ground state and disappears in the excited state. The intermolecular hydrogen-bond between SS-NH 2 and CF 3CH 2OH molecules block the reorientation of the amino group and prevent the occurrence of the ICT. Therefore, no exciplex emission was recorded for SS-NH 2 in the mixed (CH 2Cl 2:CF 3CH 2OH) solvents.

Visible Light Excitable Zn2+ Fluorescent Sensor Derived from an Intramolecular Charge Transfer Fluorophore and Its in Vitro and in Vivo Application

The UV- and sensor-induced interferences to living systems pose a barrier for in vivo Zn(2+) imaging. In this work, an intramolecular charge transfer (ICT) fluorophore of smaller aromatic plane, 4-amino-7-nitro-2,1,3-benzoxadiazole, was adopted to construct visible light excited fluorescent Zn(2+) sensor, NBD-TPEA. This sensor demonstrates a visible ICT absorption band, a large Stokes shift, and biocompatibility. It emits weakly (Phi = 0.003) without pH dependence at pH 7.1-10.1, and the lambda(ex) and lambda(em) are 469 (epsilon(469) = 2.1 x 10(4) M(-1) cm(-1)) and 550 nm, respectively. The NBD-TPEA displays distinct selective Zn(2+)-amplified fluorescence (Phi = 0.046, epsilon(469) = 1.4 x 10(4) M(-1) cm(-1)) with emission shift from 550 to 534 nm, which can be ascribed to the synergic Zn(2+) coordination by the outer bis(pyridin-2-ylmethyl)amine (BPA) and 4-amine. The Zn(2+) binding ratio of NBD-TPEA is 1:1. By comparison with its analogues NBD-BPA and NBD-PMA, which have no Zn(2+) affinity, the outer BPA in NBD-TPEA should be responsible for the Zn(2+)-induced photoinduced electron transfer blockage as well as for the enhanced Zn(2+) binding ability of 4-amine. Successful intracellular Zn(2+) imaging on living cells with NBD-TPEA staining exhibited a preferential accumulation at lysosome and Golgi with dual excitability at either 458 or 488 nm. The intact in vivo Zn(2+) fluorescence imaging on zebrafish embryo or larva stained with NBD-TPEA revealed two zygomorphic luminescent areas around its ventricle which could be related to the Zn(2+) storage for the zebrafish development. Moreover, high Zn(2+) concentration in the developing neuromasters of zebrafish can be visualized by confocal fluorescence imaging. This study demonstrates a novel strategy to construct visible light excited Zn(2+) fluorescent sensor based on ICT fluorophore other than xanthenone analogues. Current data show that NBD-TPEA staining can be a reliable approach for the intact in vivo Zn(2+) imaging of zebrafish larva as well as for the clarification of subcellular distribution of Zn(2+) in vitro.