Near-IR emissive chlorin-bacteriochlorin energy-transfer dyads with a common donor and acceptors with tunable emission wavelength

Simultaneous multicolor imaging of lymph node chains using hydroporphyrin-doped near-infrared-emitting polymer dots

Aim: Evaluation of lymphatic drainage can be challenging to differentiate between separate drainage basins because only one 'color' is typically employed in sentinel node studies. This study aimed to test the feasibility of multicolor in vivo lymphangiography using newly developed organic polymer dots. Materials & methods: Biocompatible, purely organic, hydroporphyrin-doped near-infrared-emitting polymer dots were developed and evaluated for in vivo multicolor imaging in mouse lymph nodes. Results & conclusion: The authors demonstrated successful multicolor in vivo fluorescence lymphangiography using polymer dots, each tuned to a different emission spectrum. This allows minimally invasive visualization of at least four separate lymphatic drainage basins using fluorescent nanoparticles, which have the potential for clinical translation.

Synthesis of bacteriochlorins bearing diverse β-substituents

Eleven bacteriochlorins have been prepared for surface attachment, bioconjugation, water-solubilization, vibrational studies, and elaboration into multichromophore arrays.

Spacer Cation Alloying in Ruddlesden-Popper Perovskites for Efficient Red Light-Emitting Diodes with Precisely Tunable Wavelengths

Perovskite light-emitting diodes (PeLEDs) have recently shown significant progress with external quantum efficiencies (EQEs) exceeding 20%. However, PeLEDs with pure-red (620-660 nm) light emission, an essential part for full-color displays, remain a great challenge. Herein, a general approach of spacer cation alloying is employed in Ruddlesden-Popper perovskites (RPPs) for efficient red PeLEDs with precisely tunable wavelengths. By simply tuning the alloying ratio of dual spacer cations, the thickness distribution of quantum wells in the RPP films can be precisely modulated without deteriorating their charge-transport ability and energy funneling processes. Consequently, efficient PeLEDs with tunable emissions between pure red (626 nm) and deep red (671 nm) are achieved with peak EQEs up to 11.5%, representing the highest values among RPP-based pure-red PeLEDs. This work opens a new route for color tuning, which will spur future developments of pure-red or even pure-blue PeLEDs with high performance.

Aggregation-induced emission (AIE)-guided dynamic assembly for disease imaging and therapy

The phenomenon of aggregation-induced emission (AIE) is inseparable from molecular aggregation and self-assembly. Therefore, the combination of AIE and supramolecular self-assembly is well-matched. AIE-guided dynamic assembly (AGDA) could effectively respond to the endogenous stimuli (such as pH, enzymes, redox molecules) and exogenous stimuli (temperature, light, ultrasound) in the disease microenvironment, so as to achieve specific imaging and diagnosis of the disease lesions. Moreover, AGDA also dynamically adjust the intramolecular motions of AIE molecules, thereby adjusting the energy dissipation pathways and realizing the switch between photodynamic therapy and photothermal therapy for superior therapeutic effects. In this review, we aim to give an overview of the constructing strategies, stimuli-responsive imaging, regulation of intramolecular motion of AGDA in recent years, which is expected to grasp the research status and striving directions of AGDA for imaging and therapy.

Weakly conjugated bacteriochlorin-bacteriochlorin dyad: Synthesis and photophysical properties

Dyads containing two near-infrared absorbing and emitting bacteriochlorins with distinct spectral properties have been prepared and characterized by absorption, emission, and transient-absorption spectroscopies. The dyads exhibit ultrafast ([Formula: see text]3 ps) energy transfer from the bacteriochlorin with the higher-energy S1 state to the bacteriochlorin emitting at the longer wavelength. The dyads exhibit strong fluorescence and relatively long excited state lifetimes ([Formula: see text]4 ns) in both non-polar and polar solvents, which indicates negligible photoinduced electron transfer between the two bacteriochlorins in the dyads. These dyads are thus attractive for the development of light-harvesting arrays and fluorophores for in vivo bioimaging.

Solvent-dependent energy and charge transfer dynamics in hydroporphyrin-BODIPY arrays

Arrays of hydroporphyrins with boron complexes of dipyrromethene (BODIPY) are a promising platform for biomedical imaging or solar energy conversion, but their photophysical properties have been relatively unexplored. In this paper, we use time-resolved fluorescence, femtosecond transient absorption spectroscopy, and density-functional-theory calculations to elucidate solvent-dependent energy and electron-transfer processes in a series of chlorin- and bacteriochlorin-BODIPY arrays. Excitation of the BODIPY moiety results in ultrafast energy transfer to the hydroporphyrin moiety, regardless of the solvent. In toluene, energy is most likely transferred via the through-space Förster mechanism from the S₁ state of BODIPY to the S₂ state of hydroporphyrin. In DMF, substantially faster energy transfer is observed, which implies a contribution of the through-bond Dexter mechanism. In toluene, excited hydroporphyrin components show bright fluorescence, with quantum yield and fluorescence lifetime comparable to those of the benchmark monomer, whereas in DMF, moderate to significant reduction of both quantum yield and fluorescence lifetime are observed. We attribute this quenching to photoinduced charge transfer from hydroporphyrin to BODIPY. No direct spectral signature of the charge-separated state is observed, which suggests that either (1) the charge-separated state decays very quickly to the ground state or (2) virtual charge-separated states, close in energy to S₁ of hydroporphyrin, promote ultrafast internal conversion.

Synthesis of Hangman Chlorins

Two complementary rational synthetic routes have been developed in order to synthesize hangman chlorins, which differ with regard to the order of the installation (pre- and post-formation of the chlorin macrocycle) and position of the xanthene backbone about the chlorin periphery. The versatility of the synthetic method is demonstrated with the preparation of ten new hangman chlorins bearing a xanthene backbone and a pendant carboxylic acid. Cyclic voltammograms of hangman chlorins exhibit a hangman effect derived from intermolecular proton transfer. This hangman effect is manifested in catalytic hydrogen evolution production.

Synthesis of Porphyrin and Bacteriochlorin Glycoconjugates through CuAAC Reaction Tuning

Rapid and reproducible access to a series of unique porphyrin and bacteriochlorin glycoconjugates, including meso-glycosylated porphyrins and bacteriochlorins, and beta-glycosylated porphyrins, via copper catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) is reported for the first time. The work presented highlights the system-dependent reaction conditions required for glycosylation to porphyrins and bacteriochlorins based on the unique electronic properties of each ring system. Attenuated reaction conditions were used to synthesize fifteen new glycosylated porphyrin and bacteriochlorin analogs in 74 - 99% yield, and were extended to solid support to produce the first oligo(amidoamine)-based porphyrin glycoconjugate. These compounds hold significant potential as next generation water soluble catalysts and photodynamic therapy/photodynamic inactivation (PDT/PDI) agents.

Annulated bacteriochlorins for near-infrared photophysical studies

Bacteriochlorins with phenaleno or benzo annulation absorb at 913 or 1033 nm and exhibit excited-state lifetimes of 150 or 7 ps, suggesting applications in photoacoustic imaging.

Structure and conformation of photosynthetic pigments and related compounds. 15. Conformational analysis of chlorophyll derivatives – implications for hydroporphyrinsin vivo

Controlling the function of chlorophylls depends in part on their 3D conformation. The NSD program presents a powerful tool to identify the distortion modes in phytochlorins.

Activatable Near-Infrared Fluorescence Imaging Using PEGylated Bacteriochlorin-Based Chlorin and BODIPY-Dyads as Probes for Detecting Cancer

Near infrared (NIR) fluorescent probes are attractive tools for biomedical in vivo imaging due to the relatively deeper tissue penetration and lower background autofluorescence. Activatable probes are turned on only after binding to their target, further improving target to background ratios. However, the number of available activatable NIR probes is limited. In this study, we introduce two types of activatable NIR fluorophores derived from bacteriochlorin: chlorin-bacteriochlorin energy-transfer dyads and boron-dipyrromethene (BODIPY)-bacteriochlorin energy-transfer dyads. These fluorophores are characterized by multiple narrow excitation bands with relatively strong emission in the NIR. Targeted bacteriochlorin-based antibody or peptide probes have been previously limited by aggregation after conjugation. Polyethylene glycol (PEG) chains were added to improve the hydrophilicity without altering pharmacokinetics of the targeting moieties. These PEGylated bacteriochlorin-based activatable fluorophores have potential as targeted activatable, multicolor NIR fluorescent probes for in vivo applications.

BODIPY-Bacteriochlorin Energy Transfer Arrays: Toward Near-IR Emitters with Broadly Tunable, Multiple Absorption Bands

A series of energy transfer arrays, comprising a near-IR absorbing and emitting bacteriochlorin, and BODIPY derivatives with different absorption bands in the visible region (503-668 nm) have been synthesized. Absorption band of BODIPY was tuned by installation of 0, 1, or 2 styryl substituents [2-(2,4,6-trimethoxyphenyl)ethenyl], which leads to derivatives with absorption maxima at 503, 587, and 668 nm, respectively. Efficient energy transfer (>0.90) is observed for each dyad, which is manifested by nearly exclusive emission from bacteriochlorin moiety upon BODIPY excitation. Fluorescence quantum yield of each dyad in nonpolar solvent (toluene) is comparable with that observed for corresponding bacteriochlorin monomer, and is significantly reduced in solvent of high dielectric constants (DMF), most likely by photoinduced electron transfer. Given the availability of diverse BODIPY derivatives, with absorption between 500-700 nm, BODIPY-bacteriochlorin arrays should allow for construction of near-IR emitting agents with multiple and broadly tunable absorption bands. Solvent-dielectric constant dependence of Φf in dyads gives an opportunity to construct environmentally sensitive fluorophores and probes.

Characterization of Hydroporphyrins Covalently Attached to Si(100)

Attachment of synthetic analogs of natural tetrapyrroles to electroactive surfaces enables physicochemical interrogation and may provide material for use in catalysis, diagnostics, and energy conversion. Six synthetic zinc chlorins and one free base bacteriochlorin, tailored analogs of chlorophyll and bacteriochlorophyll, respectively, have been attached to Si(100) via a high-temperature (400°C) baking method. The hydroporphyrins bear diverse functional groups that enable surface attachment (vinyl, acetyl, triisopropylsilylethynyl, pentafluorophenyl, and hydroxymethylphenyl) and a geminal dimethyl group in each reduced ring for stabilization toward adventitious dehydrogenation. The films were examined by cyclic voltammetry, FTIR spectroscopy, X-ray photoelectron spectroscopy, and ellipsometry. Monofunctionalized and difunctionalized hydroporphyrins gave monolayer and multilayer films, respectively, indicating robustness of the hydroporphyrin molecules, but in each case the film was more heterogeneous than observed with comparable porphyrins. The data suggest that some amount of unattached molecules remain intercalated with surface-attached molecules. Additional molecular designs will need to be examined to develop a deep understanding of the structure-activity relationship for formation of homogeneous monolayers and multilayers of synthetic hydroporphyrins.

Amphiphilic BODIPY-Hydroporphyrin Energy Transfer Arrays with Broadly Tunable Absorption and Deep Red/Near-Infrared Emission in Aqueous Micelles

BODIPY-hydroporphyrin energy transfer arrays allow for development of a family of fluorophores featuring a common excitation band at 500 nm, tunable excitation band in the deep red/near-infrared window, and tunable emission. Their biomedical applications are contingent upon retaining their optical properties in an aqueous environment. Amphiphilic arrays containing PEG-substituted BODIPY and chlorins or bacteriochlorins were prepared and their optical and fluorescence properties were determined in organic solvents and aqueous surfactants. The first series of arrays contains BODIPYs with PEG substituents attached to the boron, whereas in the second series, PEG substituents are attached to the aryl at the meso positions of BODIPY. For both series of arrays, excitation of BODIPY at 500 nm results in efficient energy transfer to and bright emission of hydroporphyrin in the deep-red (640-660 nm) or near-infrared (740-760 nm) spectral windows. In aqueous solution of nonionic surfactants (Triton X-100 and Tween 20) arrays from the second series exhibit significant quenching of fluorescence, whereas properties of arrays from the first series are comparable to those observed in polar organic solvents. Reported arrays possess large effective Stokes shift (115-260 nm), multiple excitation wavelengths, and narrow, tunable deep-red/near-IR fluorescence in aqueous surfactants, and are promising candidates for a variety of biomedical-related applications.

Synthesis and Spectral Properties of meso-Arylbacteriochlorins, Including Insights into Essential Motifs of their Hydrodipyrrin Precursors

Synthetic bacteriochlorins-analogues of bacteriochlorophylls, Nature's near-infrared absorbers-are attractive for diverse photochemical studies. meso-Arylbacteriochlorins have been prepared by the self-condensation of a dihydrodipyrrin-carbinol or dihydrodipyrrin-acetal following an Eastern-Western (E-W) or Northern-Southern (N-S) joining process. The bacteriochlorins bear a gem-dimethyl group in each pyrroline ring to ensure stability toward oxidation. The two routes differ in the location of the gem-dimethyl group at the respective 3- or 2-position in the dihydrodipyrrin, and the method of synthesis of the dihydrodipyrrin. Treatment of a known 3,3-dimethyldihydrodipyrrin-1-carboxaldehyde with an aryl Grignard reagent afforded the dihydrodipyrrin-1-(aryl)carbinol, and upon subsequent acetylation, the corresponding dihydrodipyrrin-1-methyl acetate (dihydrodipyrrin-acetate). Self-condensation of the dihydrodipyrrin-acetate gave a meso-diarylbacteriochlorin (E-W route). A 2,2-dimethyl-5-aryldihydrodipyrrin-1-(aryl)carbinol underwent self-condensation to give a trans-A₂B₂-type meso-tetraarylbacteriochlorin (N-S route). In each case, the aromatization process entails a 2e^-/2H⁺ (aerobic) dehydrogenative oxidation following the dihydrodipyrrin self-condensation. Comparison of a tetrahydrodipyrrin-acetal (0%) versus a dihydrodipyrrin-acetal (41%) in bacteriochlorin formation and results with various 1-substituted dihydrodipyrrins revealed the importance of resonance stabilization of the reactive hydrodipyrrin intermediate. Altogether 10 new dihydrodipyrrins and five new bacteriochlorins have been prepared. The bacteriochlorins exhibit characteristic bacteriochlorophyll-like absorption spectra, including a Q_y band in the region 726-743 nm.

Synthesis and photophysical characterization of bacteriochlorins equipped with integral swallowtail substituents

The two pyrroline units of bacteriochlorins can now bear gem-dialkyl or diaryl groups (L), which project above and below the macrocycle plane, whereas dimethyl groups generally have been accessible previously.

Synthesis, photophysics and electronic structure of oxobacteriochlorins

Synthetic oxobacteriochlorins exhibit strong absorption in the deep-red window flanked by chlorins to the red and bacteriochlorins to the near-infrared.

Bioconjugatable, PEGylated Hydroporphyrins for Photochemistry and Photomedicine. Narrow-Band, Near-Infrared-Emitting Bacteriochlorins

Synthetic bacteriochlorins absorb in the near-infrared (NIR) region and are versatile analogues of natural bacteriochlorophylls. The utilization of these chromophores in energy sciences and photomedicine requires the ability to tailor their physicochemical properties, including the incorporation of units to impart water solubility. Herein, we report the synthesis, from two common bacteriochlorin building blocks, of five wavelength-tunable, bioconjugatable and water-soluble bacteriochlorins along with two non-bioconjugatable benchmarks. Each bacteriochlorin bears short polyethylene glycol (PEG) units as the water-solubilizing motif. The PEG groups are located at the 3,5-positions of aryl groups at the pyrrolic β-positions to suppress aggregation in aqueous media. A handle containing a single carboxylic acid is incorporated to allow bioconjugation. The seven water-soluble bacteriochlorins in water display Q_y absorption into the NIR range (679-819 nm), sharp emission (21-36 nm full-width-at-half-maximum) and modest fluorescence quantum yield (0.017-0.13). Each bacteriochlorin is neutral (non-ionic) yet soluble in organic (e.g., CH₂Cl₂, DMF) and aqueous solutions. Water solubility was assessed using absorption spectroscopy by changing the concentration ∼1000-fold (190-690 µM to 0.19-0.69 µM) with a reciprocal change in pathlength (0.1-10 cm). All bacteriochlorins showed excellent solubility in water, except for a bacteriochlorin-imide that gave slight aggregation at higher concentrations. One bacteriochlorin was conjugated to a mouse polyclonal IgG antibody for use in flow cytometry with compensation beads for proof-of-principle. The antibody conjugate of B2-NHS displayed a sharp signal upon ultraviolet laser excitation (355 nm) with NIR emission measured with a 730/45 nm bandpass filter. Overall, the study gives access to a set of water-soluble bacteriochlorins with desirable photophysical properties for use in multiple fields.

Bioconjugatable, PEGylated Hydroporphyrins for Photochemistry and Photomedicine. Narrow-Band, Red-Emitting Chlorins

Chromophores that absorb and emit in the red spectral region (600-700 nm), are water soluble, and bear a bioconjugatable tether are relatively rare yet would fulfill many applications in photochemistry and photomedicine. Here, three molecular designs have been developed wherein stable synthetic chlorins - analogues of chlorophylls - have been tailored with PEG groups for use in aqueous solution. The designs differ with regard to order of the installation (pre/post-formation of the chlorin macrocycle) and position of the PEG groups. Six PEGylated synthetic chlorins (three free bases, three zinc chelates) have been prepared, of which four are equipped with a bioconjugatable (carboxylic acid) tether. The most effective design for aqueous solubilization entails facial encumbrance where PEG groups project above and below the plane of the hydrophobic disk-like chlorin macrocycle. The chlorins possess strong absorption at ~400 nm (B band) and in the red region (Q_y band); regardless of wavelength of excitation, emission occurs in the red region. Excitation in the ~400 nm region thus provides an effective Stokes shift of >200 nm. The four bioconjugatable water-soluble chlorins exhibit Q_y absorption/emission in water at 613/614, 636/638, 698/700 and 706/710 nm. The spectral properties are essentially unchanged in DMF and water for the facially encumbered chlorins, which also exhibit narrow Q_y absorption and emission bands (full-width-at-half maximum of each <25 nm). The water-solubility was assessed by absorption spectroscopy over the concentration range ~0.4 μM - 0.4 mM. One chlorin was conjugated to a mouse polyclonal IgG antibody for use in flow cytometry with compensation beads for proof-of-principle. The conjugate displayed a sharp signal when excited by a violet laser (405 nm) with emission in the 620-660 nm range. Taken together, the designs described herein augur well for development of a set of spectrally distinct chlorins with relatively sharp bands in the red region.

Synthesis and photophysical characteristics of 2,3,12,13-tetraalkylbacteriochlorins

Tetraalkylbacteriochlorins, available upon acid-mediated self-condensation of α-ester stabilized dihydrodipyrrin-carboxaldehydes, provide valuable models of the naturally occurring bacteriochlorophylls.

Elaboration of an unexplored substitution site in synthetic bacteriochlorins

The ability to introduce substituents at designated sites about the perimeter of synthetic bacteriochlorins – analogs of bacteriochlorophylls of bacterial photosynthesis – remains a subject of ongoing study. Here, the self-condensation of a dihydrodipyrrin-dioxolane affords a 5-[2-(trimethylsiloxy)ethoxy]bacteriochlorin. Like a 5-methoxybacteriochlorin, the latter undergoes regioselective bromination at the 15-position, directed by the distal 5-alkoxy group. On the other hand, attempted bromination of a bacteriochlorin bearing a 5-(2-hydroxyethoxy) group resulted in intramolecular ether formation with the adjacent β-pyrroline position to give an annulated dioxepine ring (confirmed by single-crystal X-ray structural analysis). The hydroxyethoxy group at the 5-position can be derivatized by acylation. In addition, the installation of auxochromes (methoxycarbonyl, phenylethynyl) at the β-pyrrole rings causes a substantial bathochromic shift of the long-wavelength absorption band (812 nm) and companion fluorescence emission band (821 nm). Taken together, the modification of the 5-substituent complements existing methods for installing a single substituent on the bacteriochlorin macrocycle.

Progress Towards Synthetic Chlorins with Graded Polarity, Conjugatable Substituents, and Wavelength Tunability

Advances in chlorin synthetic chemistry now enable the de novo preparation of diverse chlorin-containing molecular architectures. Five distinct molecular designs have been explored here, including hydrophobic bioconjugatable (oxo)chlorins; a hydrophilic bioconjugatable chlorin; a trans-ethynyl/iodochlorin building block; a set of chlorins bearing electron-rich (methoxy, dimethylamino, methylthio) groups at the 3-position; and a set of ten 3,13-disubstituted chlorins chiefly bearing groups with extended π-moieties. Altogether 23 new chlorins (17 targets, 6 intermediates) have been prepared. The challenge associated with molecular designs that encompass the combination of "hydrophilic, bioconjugatable and wavelength-tunable" chiefly resides in the nature of the hydrophilic unit.

Deep-red emissive BODIPY-chlorin arrays excitable with green and red wavelengths

We report here the synthesis and characterization of BODIPY-chlorin arrays containing a chlorin subunit, with tunable deep-red (641-685 nm) emission, and one or two BODIPY moieties, absorbing at 504 nm. Two types of arrays were examined: one where BODIPY moieties are attached through a phenylacetylene linker at the 13- or 3,13-positions of chlorin, and a second type where BODIPY is attached at the 10-position of chlorin through an amide linker. Each of the examined arrays exhibits an efficient (≥0.80) energy transfer from BODIPY to the chlorin moiety in both toluene and DMF and exhibits intense fluorescence of chlorin upon excitation of BODIPY at ∼500 nm. Therefore, the effective Stokes shift in such arrays is in the range of 140-180 nm. Dyads with BODIPY attached at the 10-position of chlorin exhibit a bright fluorescence in a range of solvents with different polarities (i.e., toluene, MeOH, DMF, and DMSO). In contrast to this, some of the arrays in which BODIPY is attached at the 3- or at both 3,13-positons of chlorin exhibit significant reduction of fluorescence in polar solvents. Overall, dyads where BODIPY is attached at the 10-position of chlorin exhibit ∼5-fold brighter fluorescence than corresponding chlorin monomers, upon excitation at 500 nm.

Effects of substituents on synthetic analogs of chlorophylls. Part 4: How formyl group location dictates the spectral properties of chlorophylls b, d and f

Photosynthetic organisms are adapted to light characteristics in their habitat in part via the spectral characteristics of the associated chlorophyll pigments, which differ in the position of a formyl group around the chlorin macrocycle (chlorophylls b, d, f) or no formyl group (chlorophyll a). To probe the origin of this spectral tuning, the photophysical and electronic structural properties of a new set of synthetic chlorins are reported. The zinc and free base chlorins have a formyl group at either the 2- or 3-position. The four compounds have fluorescence yields in the range 0.19-0.28 and singlet excited-state lifetimes of ca 4 ns for zinc chelates and ca 8 ns for the free base forms. The photophysical properties of the 2- and 3-formyl zinc chlorins are similar to those observed previously for 13-formyl or 3,13-diformyl chlorins, but differ markedly from those for 7-formyl analogs. Molecular-orbital characteristics obtained from density functional theory (DFT) calculations were used as input to spectral simulations employing the four-orbital model. The analysis has uncovered the key changes in electronic structure engendered by the presence/location of a formyl group at various macrocycle positions, which is relevant to understanding the distinct spectral properties of the natural chlorophylls a, b, d and f.

Synthetic bacteriochlorins bearing polar motifs (carboxylate, phosphonate, ammonium and a short PEG). Water-solubilization, bioconjugation, and photophysical properties

A bacteriochlorin scaffold has been derivatized for life sciences applications.

Near-infrared tunable bacteriochlorins equipped for bioorthogonal labeling

Nine new near-infrared absorbing (729–820 nm) synthetic bacteriochlorins are equipped with one of four reactive groups for bioorthogonal conjugation.

Activatable organic near-infrared fluorescent probes based on a bacteriochlorin platform: synthesis and multicolor in vivo imaging with a single excitation

Near infrared (NIR) fluorescent probes are ideal for in vivo imaging because they offer deeper tissue penetration and lower background autofluorescence. Although most fluorophores in this range are cyanine-based dyes, several new classes of fluorescent NIR probes have been developed. In this study, we developed organic bacteriochlorin derivatives, NMP4 and NMP5, which are excited with a single green light and emit different narrow, well-resolved bands in the NIR (peak of 739 and 770 nm for NMP4 and NMP5, respectively). When conjugated to galactosyl-human serum albumin (hGSA) or glucosyl-human serum albumin (glu-HSA), both targeting H-type lectins, including the β-d-galactose receptor expressing on ovarian cancer, these agents become targeted, activatable, single excitation, multicolor NIR fluorescence probes. After conjugation to either glu-HSA or hGSA, substantial quenching of fluorescence occurs that is reversed after cell binding and internalization. In vitro studies showed higher cancer cell uptake with NMP4 or NMP5 conjugated to hGSA compared to the same conjugates with glu-HSA. In vivo single excitation two-color imaging was performed after intraperitoneal injection of these agents into mice with disseminated ovarian cancer. Excited with a single green light, distinct NIR emission spectra from each fluorophore were detected and could be distinguished with spectral unmixing. In vivo results using a red fluorescence protein (RFP) labeled tumor model of disseminated ovarian cancer demonstrated high sensitivity and specificity for all probes. The success of single excitation, 2-color NIR fluorescence imaging with a new class of bacteriochlorin-based activatable fluorophores, NMP4 and NMP5, paves the way for further exploration of noncyanine dye-based NIR fluorophores.