Low Fluorescence Quantum Yield Research Articles

Modulation of fluorescent protein chromophore for photodynamic therapy and two-photon fluorescent imaging in living cells

The green fluorescent protein (GFP) chromophore has been widely applied as a biological marker or viscosity sensor. However, modulation of GFP chromophore for photodynamic therapy (PDT) has rarely been reported. Inspired by this, through the unique phenothiazine-anchored strategy, a near-infrared emission photosensitizer Lys-PtzFP was designed and synthesized to achieve this process. The maximum absorption wavelength of Lys-PtzFP was 460 nm and the corresponding molar extinction coefficient was 6.60 × 104 M−1 cm−1 in MeOH. The maximum emission wavelengths of Lys-PtzFP was at 725 nm. The photosensitizer Lys-PtzFP showed a high singlet oxygen quantum yield (ΦΔ = 0.42) and low fluorescence quantum yield (φF = 0.002) in MeOH. Besides, Lys-PtzFP possessed high specificity for lysosomes with negligible dark cytotoxicity (MTT assay >94.6%), good photostability and low half-maximal inhibitory concentration (IC50) of 0.93 μM. Finally, the intracellular photodynamic therapy experiments revealed that Lys-PtzFP can produce singlet oxygen in lysosomes and induce apoptosis under irradiation. In conclusion, Lys-PtzFP could be a promising photosensitizer for PDT and two-photon imaging applications. This type of photosensitizer can inspire the development of new photosensitizers for further explore highly efficient PDT.

Remarkable Increase of Fluorescence Quantum Efficiency by Cyano Substitution on an ESIPT Molecule 2-(2-Hydroxyphenyl)benzothiazole: A Highly Photoluminescent Liquid Crystal Dopant

Fluorescent molecules with excited-state intramolecular proton transfer (ESIPT) character allow the efficient solid-state luminescence with large Stokes shift that is important for various applications, such as organic electronics, photonics, and bio-imaging fields. However, the lower fluorescence quantum yields (ΦFL) in the solution or viscous media, due to their structural relaxations in the excited state to reach the S0/S1 conical intersection, shackle further applications of ESIPT-active luminophores. Here we report that the introduction of a cyano group (-CN) into the phenyl group of 2-(2-hydroxyphenyl)benzothiazole (HBT), a representative ESIPT compound, remarkably increase its fluorescence quantum yield (ΦFL) from 0.01 (without -CN) to 0.49 (with -CN) in CH2Cl2, without disturbing its high ΦFL (=0.52) in the solid state. The large increase of the solution-state ΦFL of the cyano-substituted HBT (CN-HBT) is remarkable, comparing with our previously reported ΦFL values of 0.05 (with 4-pentylphenyl), 0.07 (with 1-hexynyl), and 0.15 (with 4-pentylphenylethynyl). Of interest, the newly-synthesized compound, CN-HBT, is miscible in a conventional room-temperature nematic liquid crystal (LC), 4-pentyl-4′-cyano biphenyl (5CB), up to 1 wt% (~1 mol%), and exhibits a large ΦFL of 0.57 in the viscous LC medium. A similar ΦFL value of ΦFL = 0.53 was also recorded in another room-temperature LC, trans-4-(4-pentylcyclohexyl)benzonitrile (PCH5), with a doping ratio of 0.5 wt% (~0.5 mol%). These 5CB/CN-HBT and PCH5/CN-HBT mixtures serve as light-emitting room-temperature LCs, and show anisotropic fluorescence with the dichroic ratio of 3.1 upon polarized excitation, as well as electric field response of luminescence intensity changes.

Optical-Property-Enhancing Novel Near-Infrared Active Niosome Nanoformulation for Deep-Tissue Bioimaging.

Indocyanine green (ICG) is a clinically approved near-infrared (NIR) contrast agent used in medical diagnosis. However, ICG has not been used to its fullest for biomedical imaging applications due to its low fluorescence quantum yield, aqueous instability, concentration-dependent aggregation, and photo and thermal degradations, leading to quenching of its fluorescence emission. In the present study, a nanosized niosomal formulation, ICGNiosomes (ICGNios), is fabricated to encapsulate and protect ICG from degradation. Interestingly, compared to free ICG, the ICGNios exhibited higher fluorescence quantum yield and fluorescence emission with a bathochromic shift. Also, ICGNios nanoparticles are biocompatible, biodegradable, and readily uptaken by the cells. Furthermore, ICGNios show more enhanced fluorescence intensity through ∼1 cm thick chicken breast tissue compared to free ICG, which showed minimal emission through the same thickness of tissue. Our results suggest that ICGNios could offer a promising platform for deep-tissue NIR in vivo imaging to visualize inaccessible tissue microstructures for disease diagnosis and therapeutics.

Unveiling the photophysical, biomolecule binding and photo-oxidative capacity of novel Ru(II)-polypyridyl corroles: A multipronged approach

Two fluorinated corrole derivatives, namely H3MebpyCor and RuMebpyCor, were synthesized and characterized in terms of their photophysical, electrochemical, and photooxidation behavior. Their biomolecular binding capacity toward Human Serum Albumin (HSA) and calf thymus DNA (CT-DNA) was also evaluated. The experimental data were correlated with theoretical analysis via Time Dependent Density Functional Theory (TDDFT) and Molecular Docking calculations. We found an extremely low fluorescence quantum yield for both corroles dissolved in acetonitrile (CH3CN) and dimethyl sulfoxide (DMSO), which suggests a relaxation pathway through nonradiative processes, such as internal conversion. However, the internal conversion channel in RuMebpyCor competes with the energy transfer to the Ru(II) moiety, placing triplet state formation as a second mechanism of relaxation for this structure. Both corroles showed no aggregation and good photostability. The singlet oxygen (1O2) quantum yield (ΦΔ) values also highlight their potential application in photoinactivation approaches. Theoretical analysis suggests that the introduction of Ru(II) ion coordinated in the bipyridyl unit significantly alters the optically induced electronic transitions, and that the solvents play an important role in defining the optical spectra of the two corroles. Additionally, they interact spontaneously and moderate to strong via ground-state association (static process) with HSA and CT-DNA. However, for the HSA binding assays the dynamic fluorescence quenching mechanism can also occur at high corrole concentrations. Finally, in silico calculations suggest that the main binding region into CT-DNA is the minor groove, while subdomain IIA (site I) is the main binding region for HSA:H3MebpyCor (experimental proportion 1:1) and both subdomains IIA and IB (sites I and III, respectively) for HSA:RuMebpyCor (experimental proportion 1:2).

A lipid droplets specific probe for imaging of atherosclerosis and fibrocalcific bicuspid aortic valves

Lipid droplets (LDs) have been regarded as potential targets for the diagnosis of cardiovascular diseases. However, conventional LDs imaging strategies suffer from invasive sample collection and tedious histological preparations. Although fluorescence imaging has showed good performance in LDs imaging, ideal probes are still in urgent demand. In this work, fluorescent probe, namely, MeTTI was prepared for LDs visualization in cells and tissues. MeTTI exhibited low fluorescence quantum yield in dimethyl sulfoxide (Φf = 0.2 %), while the value in the solid state was obvious increased (Φf = 3.5 %), suggesting the aggregation-induced emission (AIE) property of MeTTI. Meanwhile, MeTTI would form excimers (emission ranged 750–850 nm) in water, and it showed good biocompatibility. Moreover, MeTTI exhibited impressive fluorescence emission enhancement in oleic acid (Φf = 34.7 %) compared to that in water (Φf = 1.11 %), which can specifically stain LDs in cells, atherosclerosis (AS) plaques and human fibrocalcific bicuspid aortic valves (FBAV) with high ratio of signal to noise. In addition, MeTTI could also monitor the dynamic changes of LDs in cells. These results were expected to provide a simple tool for studying the pathogenesis of cardiovascular diseases with lipid deposition and triggering enthusiasm to develop new imaging techniques for the diagnosis of these diseases.

Near-infrared-emitting difluoroboron β-diketonate dye with AIE characteristics for cellular imaging

Near-infrared (NIR) fluorophores have promoted the development of materials for bioimaging and therapy, but traditional NIR dyes usually suffer from aggregation-caused quenching (ACQ), impeding their applications. Herein, we propose a difluoroboron β-diketonate complex TTBE, consisting a donor-acceptor (D-A) structure with difluoroboron moiety as an electron acceptor and N, N-diethylaniline as well as triphenylamine (TPA)-thiophene building block as two electron donors. TTBE exhibited both solvatochromism and aggregation-induced emission (AIE) characteristics. In polar solvent DMSO, the emission maxima of TTBE were observed at 680 nm with low fluorescence quantum yield (ΦF = 0.01%), while in less polar solvent CH2Cl2, its emission maxima blue-shifted to 666 nm with increased fluorescence quantum yield (ΦF = 0.41%). The fluorescence of TTBE could be enhanced 650-fold in 90% hexane/THF mixture solution relatively to that in pure THF. Moreover, the fabricated F127/TTBE nanoparticles (NPs) showed NIR emission at 735 nm in water and excellent cytocompatibility even at high concentration (100 μg/mL). According to the results of cell imaging and flow cytometry, NPs were easily internalized into cells and distributed in the cytoplasm with strong red fluorescence. Therefore, this research inspires more insight into development of NIR AIE luminogens for biomedical imaging.

Synthesis of one-component type II dithioxanthone-disulfide photoinitiator and investigation of photophysical and photochemical properties

Herein, we report the successful synthesis of dithioxanthone-disulfide [TX-S-]2 as a new one-component type II photoinitiator. Photophysical properties of [TX-S-]2 in terms of fluorescence and phosphorescence properties were investigated and low fluorescence quantum yield was observed, which indicates an efficient intersystem crossing (ISC) that leads to the generation of triplet states. Efficiently produced initiating thiyl radicals from the triplet states lead to polymerization of methyl methacrylate with [TX-S-]2 in air atmosphere. To elucidate the initiating mechanism, a disulfide exchange reaction was performed in the presence of diphenyl disulfide [Ph-S-]2, and the obtained results from HQ-TOF confirmed that [TX-S-]2 disulfide bond cleavage occurs upon irradiation with light. Initiating mechanism of [TX-S-]2 revealed the potential usage of this compound as a self-healing agent due to the efficient cleavage of disulfide bonds. In conjunction with the experimental studies series of Density Functional Theory calculations were performed and various photophysical and photochemical properties, including HOMO and LUMO, were computationally calculated and visualized.

Role of Tau Protein on Photophysical Properties of Carbon Dots

Aggregation of intrinsically disordered Tau protein is a key biomarker of the progressive neurodegenerative disorder Alzheimer's Disease [1]. Although the precise mechanism by which tau aggregates is not well understood, abnormal post-translational modifications of tau have been implicated in the formation of tau aggregates and neurofibrillary tangles. In vitro, Tau aggregation may be detected by the fluorescent Thioflavin T dye, which is limited by non-specific interactions between the dye and other additives and low fluorescence quantum yield. CDs are a highly modifiable nanomaterials with characteristic optical properties and poorly-understood protein interactions. Using the novel fluorescent nanoallotrope, Carbon dots (CDs), we examined an alternative method for facile detection of intrinsically disordered Tau protein. Through photophysical studies of tau protein with two varieties of CDs, we determined that Tau protein decreased the fluorescent intensity of dual-fluorescing CDs to a greater extent than nitrogen-doped CDs after monitoring fluorescence. Tau protein aggregation was also induced by using heparin and this process was monitored by using ThT as well as CD assays. The CDs exhibited similar properties with heparin-aggregated tau samples and non-aggregated tau protein under specific experimental conditions. Data indicate that carbon dots are viable sensors for proteins and could be further optimized for disease biomarker detection and quantification in the development of rapid, sensitive and selective diagnostic assays.

Superradiance of bacteriochlorophyll c aggregates in chlorosomes of green photosynthetic bacteria

Chlorosomes are the main light-harvesting complexes of green photosynthetic bacteria that are adapted to a phototrophic life at low-light conditions. They contain a large number of bacteriochlorophyll c, d, or e molecules organized in self-assembling aggregates. Tight packing of the pigments results in strong excitonic interactions between the monomers, which leads to a redshift of the absorption spectra and excitation delocalization. Due to the large amount of disorder present in chlorosomes, the extent of delocalization is limited and further decreases in time after excitation. In this work we address the question whether the excitonic interactions between the bacteriochlorophyll c molecules are strong enough to maintain some extent of delocalization even after exciton relaxation. That would manifest itself by collective spontaneous emission, so-called superradiance. We show that despite a very low fluorescence quantum yield and short excited state lifetime, both caused by the aggregation, chlorosomes indeed exhibit superradiance. The emission occurs from states delocalized over at least two molecules. In other words, the dipole strength of the emissive states is larger than for a bacteriochlorophyll c monomer. This represents an important functional mechanism increasing the probability of excitation energy transfer that is vital at low-light conditions. Similar behaviour was observed also in one type of artificial aggregates, and this may be beneficial for their potential use in artificial photosynthesis.

Thiophene donor for NIR-II fluorescence imaging-guided photothermal/photodynamic/chemo combination therapy

Organic fluorophores/photosensitizers have been widely used in biological imaging and photodynamic and photothermal combination therapy in the first near-infrared (NIR-I) window. However, their applications in the second near-infrared (NIR-II) window are still limited primarily due to low fluorescence quantum yields (QYs). Here, a boron dipyrromethene (BDP) is created as a molecularly engineered thiophene donor unit with high QYs to the redshift. Thiophene insertion initiates substantial redshifts of the absorbance as compared to its counterparts in which iodine is introduced. The fluorescent molecule can be triggered by an NIR laser with a single wavelength, thereby producing emission in the NIR-II windows. Single NIR laser-triggered phototherapeutic nanoparticles (NPs) are developed by encapsulating the BDP and the chemotherapeutic drug docetaxel (DTX) by using a synthetic amphiphilic poly(styrene-co-chloromethyl styrene)-graft-poly(ethylene glycol) functionalized with folic acid (FA). These BDP-T-N-DTX-FA NPs not only show superior solubility and high singlet oxygen QY (ΦΔ=62%) but also demonstrate single NIR laser-triggered multifunctional characteristics. After intravenous administration of the NPs into 4T1 tumor-bearing mice, the accumulation of the NPs in the tumor showed a high signal-to-background ratio (11.8). Furthermore, 4T1 tumors in mice were almost eradicated by DTX released from the BDP-T-N-DTX-FA NPs under single NIR laser excitation and the combination of photodynamic therapy (PDT) and photothermic therapy (PTT). Statement of significanceThe application of organic photosensitizers is still limited primarily due to low fluorescence quantum yields (QYs) in the second near-infrared (NIR-II) window. Here, a boron dipyrromethene (BDP) as a molecularly engineered thiophene donor unit with high QYs to the redshift is created. Phototherapeutic nanoparticles (NPs) are developed by encapsulating the BDP and docetaxel (DTX) using a synthetic amphiphilic poly(styrene-co-chloromethyl styrene)-graft-poly(ethylene glycol) functionalized with folic acid (FA). These BDP-T-N-DTX-FA NPs not only show high singlet oxygen QY (ΦΔ=62%) but also demonstrate single NIR laser-triggered multifunctional characteristics and a high signal-to-background ratio (11.8). Furthermore, 4T1 tumors in mice were almost eradicated by DTX released from the BDP-T-N-DTX-FA NPs under single NIR laser excitation and the PDT/PTT combination therapy.

Detection of Carboxylesterase 1 and Chlorpyrifos with ZIF-8 Metal–Organic Frameworks Using a Red Emission BODIPY-Based Probe

In this work, a red emission fluorescent probe CBZ-BOD@zeolitic imidazolate framework-8 (ZIF-8) was fabricated based on metal-organic frameworks (MOFs) for detecting carboxylesterase 1 (CES1). The small molecule probe CBZ-BOD was first synthesized and then used to prepare the functionalized MOF material. ZIF-8 was chosen as an encapsulation shell to improve the detection properties of CBZ-BOD. Using this unique porous materials, ultrasensitive quantification of CES1 and chlorpyrifos was successfully realized. The low detection limit and high fluorescence quantum yield were calculated as 1.15 ng/mL and 0.65 for CBZ-BOD@ZIF-8, respectively. CBZ-BOD@ZIF-8 has good biocompatibility and was successfully applied to monitor the activity of CES1 in living cells. A molecular docking study was used to explore the binding of CES1 and CBZ-BOD, finding that CES1 can bind with the probe before and after hydrolysis. This type of materialized probe can inspire the development of fluorescent tools for further exploration of many pathological processes.

Corrole-Substituted Fluorescent Heme Proteins.

Although fluorescent proteins have been utilized for a variety of biological applications, they have several optical limitations, namely weak red and near-infrared emission and exceptionally broad (>200 nm) emission profiles. The photophysical properties of fluorescent proteins can be enhanced through the incorporation of novel cofactors with the desired properties into a stable protein scaffold. To this end, a fluorescent phosphorus corrole that is structurally similar to the native heme cofactor is incorporated into two exceptionally stable heme proteins: H-NOX from Caldanaerobacter subterraneus and heme acquisition system protein A (HasA) from Pseudomonas aeruginosa. These yellow-orange emitting protein conjugates are examined by steady-state and time-resolved optical spectroscopy. The HasA conjugate exhibits enhanced fluorescence, whereas emission from the H-NOX conjugate is quenched relative to the free corrole. Despite the low fluorescence quantum yields, these corrole-substituted proteins exhibit more intense fluorescence in a narrower spectral profile than traditional fluorescent proteins that emit in the same spectral window. This study demonstrates that fluorescent corrole complexes are readily incorporated into heme proteins and provides an inroad for the development of novel fluorescent proteins.

Donor-Acceptor Type [5]Helicene Derivative with Strong Circularly Polarized Luminescence

Abstract Circularly polarized luminescence (CPL) of unsubstituted helicenes is weak due to their low fluorescence quantum yield (Φf) and small dissymmetry factor (gCPL). In this study, we designed and synthesized a donor-acceptor type [5]helicene, 5,10-dicyano-2,13-bis(3,4,5-tris(n-octyloxy)phenyl)[5]helicene. This helicene showed high fluorescence quantum yield (Φf = 0.63) and good |gCPL| (4.2 × 10−3) due to symmetry-allowed transition and its helical structure. Moreover, the helicene showed solvatofluorochromism while maintaining gCPL.

Thiophene Donor for NIR-II Fluorescence Imaging Guided Photothermal/Photodynamic/Chemo Combination Therapy

Organic fluorophores/photosensitizers have been widely used in biological imaging and photodynamic and photothermal combination therapy in the first near-infrared windows. However, their applications in the second near-infrared (NIR-II) windows are still limited primarily owing to low fluorescence quantum yields (QYs). Here, a boron dipyrromethene (BDP) as the molecularly engineered thiophene donor unit with high QYs to the redshift is created. Thiophene insertion initiates substantial redshifts of the absorbance, as compared to its counterparts that introduce iodine. The fluorescent molecule can be triggered by a NIR laser with a single wavelength, producing emission in the NIR-II windows. Single NIR laser triggered phototherapeutic nanoparticles (NPs) are developed by encapsulating the BDP and chemotherapy drug docetaxel (DTX) using a synthetical amphiphilic poly(styrene- co -chloromethyl styrene)-graft-poly(ethylene glycol) functionalized with folic acid (FA). These BDP-T-N-DTX-FA NPs not only show superior solubility and high singlet oxygen quantum yield (ΦΔ =62%), but also demonstrate a single NIR laser-triggered multifunctional characteristics. After intravenous injection of the NPs into 4T1 tumor-bearing mice, the accumulation of the NPs in the tumor presented a high signal-to-background ratio (11.8). Furthermore, the 4T1 tumors in mice were almost eradicated by released DTX and PDT/PTT combination therapy from the BDP-T-N-DTX-FA NPs under the single NIR laser excitation.

Спектрально-люминесцентные свойства и фотолиз заряженных форм бисфенола А

The spectral luminescent properties and photolysis of the ionic forms (neutral, cationic and anionic) of bisphenol A have been studied experimentally and by methods of quantum chemistry. Calculations and experiment have shown that, in comparison with a neutral form, no new absorption bands appear in the absorption spectra of ionic form in the range 200–600 nm. The polar solvent (water) shifts the absorption spectrum bands of ionic forms towards low energies. In this case, the shift of the absorption spectrum of the cation is insignificant, and the shift of the anion is significant with an increase in the intensity of the absorption bands. The low quantum yield of fluorescence of ionic form is explained by the prevalence of the efficiency of singlet-triplet conversion over the efficiency of the radiation channel of decay of the fluorescent state. The low quantum yield of fluorescence of the anionic form is due not only to the effective singlet-triplet conversion, but also to the low efficiency of the radiative decay of the fluorescent state of the anion caused by a change in its orbital nature. Calculations have shown that the potential curves of the excited states of bisphenol A and its ionic forms have a significant potential barrier to photolysis. The increase in the efficiency of the process of photodissociation of the bisphenol A anion is caused by a noticeable decrease in the potential barrier and an increase in the overlap of the absorption spectra of the bisphenol A anion and solar radiation.

Naphthalimide-Based Hydrazone Derivatives: Synthesis, Mechanochromism in the Solid State and Response to Ions in Dilute Solutions.

Molecules showing mechanochromic luminescence (MCL) are promising for use in the in the fields of sensing and probes. We report the design and synthesis of new naphthalimide-based hydrazone derivatives, NI-TPE and NI-3BA. Both the luminogens are weakly emissive with s Φf =0.3 % and 0.5 % respectively when aggregated in amorphous states as strong π-π stacking and intermolecular interaction prevent luminescence. On the contrary, in the crystalline state, single crystal analysis of two derivatives shows that nonradiative decay is reduced or inhibited by molecular stacking modes and intermolecular interactions. Increases of fluorescence emission intensity to s Φf =5.5 % and 6.0 % upon solvent evaporation are attributed to weak π-π overlapping and hydrogen bonding (N-H ⋅⋅⋅ O, distance 2.99 Å), which are beneficial to the formation of molecules with a loose packing. At the same time, the packing modes that the two derivatives adopt in the crystal lattice are destroyed to result in a low solid-state fluorescence quantum yield and a bathochromic shift of 23-25 nm upon grinding. All these factors cause the two derivatives show an unusual "turn off" MCL phenomenon. The fluorescence emission, its pH reversibility, and selective response to fluoride and acetate ions of up to 91-93 % in dilute solutions were also demonstrated.

The effect of molecular structure on the efficiency of 1,4-diazine–based D–(π)–A push-pull systems for non-doped OLED applications

A series of novel D–A and D–π–A push-pull systems based on a pyrazine and quinoxaline acceptor, bearing various electron-donating triphenylamine and carbazole moieties, are compared. A significant difference in electrochemical and photophysical properties was found depending on molecular structure. The compounds have strong solvatochromic properties. Quinoxaline-containing systems exhibit delayed fluorescence (DF) in thermal vacuum deposition films. Despite the low quantum yield of fluorescence in the solid state (less than 10%), organic light-emitting diodes with sufficiently high efficiency (4.2 cd/A) have been fabricated on the basis of this push-pull systems. The best results were obtained for compounds exhibiting DF. The possible channel for increasing the efficiency of OLED can be associated with the “hot excitons” mechanism.

Determining Essential Requirements for Fluorophore Selection in Various Fluorescence Applications Taking Advantage of Diverse Structure-Fluorescence Information of Chromone Derivatives.

Herein, we report our work exploring the essential requirements for fluorophore selection during the development of various fluorescence applications. We assembled a library of chromone-derived fluorophores with diverse structure-fluorescence properties, which allowed us to choose the fluorophore pairs with similar structures but differing fluorescence properties and compared the performance of the selected fluorophore pairs in three types of commonly used fluorescence applications. We found that the selection standard of a suitable fluorophore is variable depending on the application. (1) In fluorescence imaging, fluorophores with strong and constant fluorescence under various conditions, such as a large pH range, are preferred. Notably, (2) in the detection of bioactive species, fluorophores with relatively lower fluorescence quantum yield favor the detection sensitivity. Furthermore, (3) in enzymatic assays employing fluorescence, the key parameter is the binding affinity between the fluorophore and the enzyme.

Investigation of 4,6-di(hetero)aryl-substituted pyrimidines as emitters for non-doped OLED and laser dyes

Two novel V-shaped push-pull systems based on a pyrimidine acceptor have been designed and investigated. Low-temperature measurements of the fluorescence and delayed luminescence spectra demonstrated that the emission bands of the compounds have a charge-transfer character.Despite the fact that compounds in thermal vacuum deposition films have a low fluorescence quantum yield, OLED devices based on them show high efficiency, which can be associated with the emission mechanism through delayed fluorescence. It is found that photoproducts, obtaining upon exposure to UV-irradiation of fluorophores in chloroform solution, exhibit laser activity in the red region of the spectrum.

Electronic Spectra and Photolysis of Bisphenol A in Water

A quantum chemical study of the spectral and luminescent properties of the BPA + 2H2O complex was carried out. Calculations were performed by the semi-empirical method of intermediate neglect of differential overlap using a program complex and a special parameterization. The spectral behavior of BPA in water was modeled by a complex with water molecules in the ratio 1: 2 forming the hydrogen bond. The calculated data were compared with the results of investigation of the isolated BPA molecule. The nonplanar BPA structure leads to the strong mixing of the π- and σ-type atomic wave functions. The main reason for the low quantum yield of the BPA fluorescence is the efficient process of singlet-triplet conversion in the S1(ππ*) ≳ Tn(πσ*) channel of the BPA molecule and its complex with water. A study of the photolysis of the isolated BPA molecule upon exposure to solar radiation, the short-wavelength boundary of which on the Earth’s surface is located at ~290 nm (~34480 cm–1), showed that the energy of the photodissociative state localized on the O–H bond is much higher than this value for BPA. The binding curve is characteristic of the S1(ππ*) state, while the singlet and triplet states of the πσ* type, localized on the single C–C bonds of the central fragment of the molecule, are repulsion curves with a barrier. From our point of view, the low efficiency of the BPA degradation under the influence of solar radiation is due to the presence of a significant potential barrier to the photolysis in the singlet or triplet state. The mechanisms of bond breaking in the BPA + 2H2O complex are different for the singlet and triplet states, namely, for the S3(πσ*) state, the break occurs by the predissociation mechanism, and for the Tn(πσ*) state, due to its population through the singlet-triplet conversion in the S1(ππ*) → Тn(πσ*) channel.