SOLIGENIX, INC.

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934

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Preliminary Proxy Statement.

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Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

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Definitive Proxy Statement.

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Definitive Additional Materials.

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Soliciting Material Pursuant to §240.14a-12

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SOLIGENIX, INC.

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(Name of Registrant as Specified in Its Charter)

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Fee paid previously with preliminary materials.

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Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a6(i)(1) and 0-11.

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August 3, 2026​

Dear Fellow Stockholders:

Every year, I appreciate the opportunity to write directly to you, our stockholders, to reflect on where we have been and, more importantly, where we believe Soligenix is headed. While this past year has been one of the most challenging in our Company’s history, it has also reinforced my belief that Soligenix possesses valuable scientific assets, meaningful development opportunities, and several potential avenues to pursue long-term stockholder value.

First and foremost, I want to acknowledge the disappointment surrounding our Phase 3 FLASH2 study evaluating HyBryte™ for the treatment of early-stage cutaneous T-cell lymphoma (CTCL). Like many of you, I had hoped for a different outcome. Although the study was discontinued following a planned interim analysis, I remain incredibly proud of and thankful to our employees, investigators and, especially, the patients who participated. While this result was disappointing, it does not diminish the innovation represented by HyBryte or the broader value of the Company we have built.

Importantly, HyBryte is only one component of our diversified pipeline. The Behçet’s disease program with SGX945 (dusquetide) illustrates this diversification. In a recently completed Phase 2 study, SGX945 demonstrated promising preliminary efficacy signals and was generally safe and well-tolerated. We are encouraged by these early results and believe they support continued development of SGX945, potentially opening the door to new strategic collaborations, assuming later studies continue to confirm what we have seen to date.

Our heat-stable vaccine platform, ThermoVax®, is another important strategic asset as governments continue investing in biodefense and pandemic preparedness. By reducing dependence on cold-chain distribution, ThermoVax® addresses a significant logistical challenge in vaccine deployment. We intend to continue advancing our heat-stable Bundibugyo Ebola vaccine program through government-supported development efforts while further validating a platform technology that may have applicability across multiple vaccines and biodefense countermeasures.

Beyond advancing our pipeline, we remain focused on maximizing stockholder value through a comprehensive evaluation of strategic alternatives. We have actively explored, and continue to explore, partnerships, licensing opportunities, mergers, acquisitions, financing alternatives and other corporate transactions. While we are in some later-stage discussions, as of the date of this letter, we have not entered into any definitive agreements and can make no promises that any transaction will be consummated on favorable terms or at all. Confidentiality obligations also prevent us from providing additional details regarding any ongoing discussions at this time, and we do not plan to provide further updates unless our public disclosure obligations require otherwise.

Among our most important assets is our Nasdaq listing. Maintaining our listing enhances liquidity, access to capital, strategic flexibility and our attractiveness to potential partners and acquirers. Preserving this asset is among the Board of Directors’ highest priorities, and it is directly connected to two proposals in this year’s proxy statement: a reverse split of our common stock (Proposal 2) and an increase in our authorized shares (Proposal 3). We see these measures as important steps to help us regain and maintain compliance with Nasdaq’s listing standards, although we can provide no guarantees. The Board of Directors recommends that you vote “FOR” each of them.

Despite recent challenges, I remain optimistic about our future. In my view, based on currently available information, I believe today’s market valuation does not fully reflect the combined value of our development pipeline, intellectual property estate and Nasdaq listing. Our responsibility now is to unlock that value through disciplined execution and thoughtful strategic decision-making.

On behalf of the Board of Directors and everyone at Soligenix, thank you for your continued trust, patience and support. We recognize the responsibility that comes with your investment and remain committed to creating value while advancing therapies that address serious unmet medical needs.

Sincerely,

Chairman of the Board of Directors, President and Chief Executive Officer

Note About Forward-Looking Statements: This letter contains forward-looking statements. Please see “Note About Forward-Looking Statements” elsewhere in this Proxy Statement for a description of the risks and uncertainties applicable to such statements, including those made in this letter.

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The Annual Meeting will be held entirely online. Stockholders may participate in the Annual Meeting by visiting the following website: www.virtualshareholdermeeting.com/sngx2026. To participate in the Annual Meeting, you will need the 16-digit control number included on your proxy card or on the instructions that accompanied your proxy materials.

Who May Vote:

Admittance to the virtual meeting will be limited to stockholders. The Board of Directors has fixed the close of business on July 20, 2026 as the record date for the determination of stockholders entitled to notice of and to vote at the Annual Meeting and any postponement or adjournment thereof. Accordingly, only stockholders of record at the close of business on that date will be entitled to vote at the meeting. A list of stockholders eligible to vote at the meeting will be available for inspection for a period of 10 days prior to the meeting, during regular business hours, at our corporate headquarters. If you want

to inspect the stockholder list prior to the meeting, please call our Corporate Secretary at (609) 538-8200 to schedule an appointment. In addition, the list of stockholders also will be available during the Annual Meeting through the meeting website for stockholders who choose to attend.

How to attend:

You will need to have your 16-Digit Control Number included on your proxy card or on the instructions that accompanied your proxy materials to join the Annual Meeting.

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Please Vote As Soon As Possible in one of the following ways:

By Order of the Board of Directors,

Princeton, New Jersey

August 3, 2026

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This Proxy Statement includes estimates, projections, statements relating to our business plans, objectives, and expected operating results that are “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, Section 27A of the Securities Act of 1933, and Section 21E of the Securities Exchange Act of 1934. These forward-looking statements generally are identified by the words “believe,” “project,” “expect,” “anticipate,” “estimate,” “intend,” “strategy,” “future,” “opportunity,” “plan,” “may,” “should,” “will,” “would” and similar expressions. Forward-looking statements are based on current expectations and assumptions that are subject to risks and uncertainties that may cause actual results to differ materially. We describe risks and uncertainties that could cause actual results and events to differ materially in “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” sections of our Forms 10-K and 10-Q. We undertake no obligation to update or revise publicly any forward- looking statements, whether because of new information, future events, or otherwise.