C172 pilot reported a rough running engine and loss of power and diversion to a nearby airport.

Narrative

Prior to departure I conducted a thorough preflight briefing; which included reviewing all relevant weather information; route planning; and emergency procedures. I ensured that the aircraft was properly fueled and inspected; verifying that all systems were functioning normally. I also briefed the flight plan; including my IFR route; as well as the planned initial altitude and any potential contingency plans in the event of an emergency. The briefing included review of the aircraft's emergency checklist; alternate airports; and the expected route of flight.I initiated the engine start sequence per the checklist; received my IFR clearance; and taxied to the designated run-up area at ZZZ1. After completing the required preflight checks; I performed a thorough engine run-up as outlined in the checklist. The magneto checks were conducted; and all engine parameters were within the acceptable green range; indicating no immediate mechanical concerns. I was cleared for takeoff from Runway XX and departed on a 280° heading; climbing to an altitude of 2;000 feet. After crossing 2;000 feet; I was cleared by Approach Control to proceed directly to ZZZ2. Shortly thereafter; I received clearance to climb to 5;000 feet while continuing direct to ZZZ2. During cruise flight at approximately 5;000 feet; I began to experience noticeable engine roughness. In response; I initiated troubleshooting procedures using the checklist; which included adjusting mixture; verifying fuel settings; and checking engine parameters. Despite these actions; the roughness persisted; leading me to assess my options for a safe landing.I promptly notified Approach Control of my intention to circle to the nearest suitable airport; as the engine roughness was affecting my ability to maintain full power. I communicated that I was unable to safely continue to my original destination and requested assistance in identifying the closest available landing site. Approach directed me to an airport approximately 2 miles away from my current position. As the situation developed; I realized that the airport in question was located approximately 2 miles from ZZZ3; with limited options for alternate landing sites within gliding distance. With engine performance degraded; I determined this airport to be the best option for a forced landing; given its proximity and the inability to reach other viable airports within my glide range.Further communications with Approach Control revealed that the airport lacked a pilot-controlled lighting system; complicating the landing due to the night-time conditions. In response; Approach Control [granted priority handling] and coordinated with a nearby helicopter; which was positioned to provide a spotlight on the runway to assist with my landing. I proceeded to circle the airport approximately 7 to 8 times; maintaining visual contact with the helicopter as it provided the necessary runway illumination. Once the spotlight was effectively positioned; I was able to maneuver the aircraft safely into position and execute a successful landing. After landing on the runway; I exited and maneuvered the aircraft off the runway and to a safe parking area. I then completed engine shutdown procedures. Upon securing the aircraft; I contacted local law enforcement officers on site; who cleared me to leave the area. I was informed that a mechanic would be dispatched the following day to inspect the aircraft for any potential issues. Fortunately; no injuries or damage to the aircraft occurred during the event. The situation was handled in a calm and controlled manner; and the coordination between Approach Control and the helicopter significantly contributed to the safe resolution of the emergency.